A2IM (American Association of Independent Music) "...
serves the Independent music community as a unified voice representing a broad coalition of music labels ... ."
AAAF (American Academy of Audiology Foundation) Their mission: "To promote philanthropy in support of research, education, and public awareness in audiology and hearing science." [From website.]
AAC (Advanced Audio Coding) Shortened name for the MPEG-2 Advanced
Audio Coding specification, declared an international standard by MPEG in April 1997; however, now the term is used also to refer to MPEG-4 advanced audio coding.
Made most popular by Apple using it for compressing audio CDs for their iPod and iTunes products.
AAM (Academy of Ancient Music) Founded by British musician Christopher Hogwood in 1973. They perform using instruments that date from the time when the music was composed. "Under Hogwood’s visionary leadership, it established itself as a leading authority on how music was originally performed: this pioneering work had a transformative impact on the world of classical music, and lies at the heart of the AAM’s reputation for musical excellence."
AAM (American
Association of Museums)
"AAM’s mission is to enhance the value of museums to their communities through leadership, advocacy, and service." Valuable resource for sound contractors, integrators, etc.
AB Microphones. A stereo recording technique whereby two microphones are spaced apart (anywhere from about 3 feet to as much as 10 feet) to create a time difference between them that the human brain perceives and translates into stereo localization and imaging. Also called time-difference recording.
ABA (Audio Branding Academy) "The Audio Branding Academy was founded by Cornelius Ringe, Kai Bronner and Rainer Hirt in Hamburg in February 2009. It is the first independent institution for acoustic brand communication, aiming at promoting an intentional and responsible use of acoustic stimuli within brand communication.
The Audio Branding Academy is a unique competence center for intersection points of brands, sound and environment and combines a forum, think tank, expert network and education. It hosts the annual Audio Branding Congress and regularly organizes workshops on various audio branding related topics." [From website; hit link]
abbreviation 1. The act or product
of shortening. 2. A shortened form of a word or phrase used chiefly in
writing to represent the complete form, such as Mass. for Massachusetts
or USMC for United States Marine Corps. [AHD]
Compare with acronym and initialism.
Abe, Yoshiharu(1931 -2013) One of the founders of TEAC, inventor of the Portastudio® and consider the father of personal multitrack recording.
Abffusor® Registered trademark of RPG Diffusor Systems for their proprietary panel combining absorption and diffusion characteristics.
absolute pitch Music. The ability to name the pitch of a note, or to sing a named note, without reference to a previously sounded one. It is sometimes called 'perfect pitch.' [Sadie]
absorption To absorb is to receive
(an impulse) without echo or recoil: a fabric that absorbs sound; a
bumper that absorbs impact; therefore absorption is the act
or process of absorbing. [AHD] The absorption of sound is the process by which
sound energy is diminished when passing through a medium or when striking
a surface, i.e., sound is attenuated by absorption. [AHD]
The physical mechanism is usually the conversion of sound into heat, i.e.
sound molecules lose energy upon striking the material's atoms, which become
agitated, which we characterized as warmth; thus, absorption is literally
the changing of sound energy to heat. A material's ability to absorb sound
is quantified by its absorption
coefficient, whose value ranges between 0 (total reflection)
and 1 (total absorption), and just to keep things interesting, varies with
sound frequency and the angle of incidence. See Siegfried Linkwitz's Acoustic
absorption and acoustic resistors; contrast with isolation.
A-B testing (or A/B testing) A comparison testing methodology
where a first test, A, is compared against a second test, B.
ABX testing (aka ABX double-blind
comparator) A system controller for audio component comparison testing
where the listener hears sound-A, sound-B, and sound-X. The listener must
make a determination as to whether X is A or B. The subject may go back
to A and B as often and for as long as necessary to make a determination.
The listener knows that A and B are different and that X is either A or B, so there is always a correct answer. The "double-blind"
part comes from neither the tester nor the listener (can be the same) knows
what source is A, B or X, only the controller knows, which is downloaded
after the test is complete to determine the results. First invented in
1977 by Arnold Krueger and Bern Muller (of the famous Southeastern Michigan
Woofer and Tweeter Marching Society or SMWTMS), later refined and marketed
by David Clark and his ABX Company. [For complete details see David L.
Clark, "High-Resolution Subjective Testing Using a Double-Blind Comparator", J. Audio Eng. Soc., Vol. 30 No. 5, May 1982, pp. 330-338.]
AC Abbreviation for air conditioning. [Some of you may wonder why this entry is included in the pro audio reference. Well it is here because back in 1880 a very early air conditioning system was patented by R. Portner and B. E. J. Eils (US Patent 229,750, Process of and Apparatus for Cooling Air) for use in their brewery, creating the very first air conditioned building for making beer, without which the pro audio industry would collapse.]
AC-3 (audio coding 3) Dolby's digital audio data compression algorithm
adopted for HDTV transmission and used in
DVDs, laserdiscs and CDs for 5.1 multichannel home theater use. See Dolby
Digital. Competes with DTS Consumer.
The terms AC-1 and AC-2 are other versions developed by Dolby
for different applications. [See Usage Note under AES3 for transmission gotcha caveats.]
Academy curve The name of the standard
mono optical track that has been around since the beginning of sound for
film. Standardized in 1938, it has improved (very) slightly over the years.
Also known as the N (normal) curve the response is flat 100
Hz-1.6 kHz, and is down 7 dB at 40 Hz, 10 dB at 5 kHz and 18 dB at 8 kHz.
This drastic "dumping" of the high-end was to hide the high-frequency "frying"
and "crackling" noise inherent in early film sound production. Compare
with X curve.
a cappella Music. Without instrumental accompaniment.
[AHD]
Accelerated-Slope™ A trademark of Rane Corporation used to describe their family of patented
tone control technologies that produce steeper slopes than normal, thus
allowing boost/cut of high and low frequencies without disturbing the critical
midband frequencies.
accommodation Said to be the most misspelled word in American
writing (two "c"s and two "m"s).
accordion "An instrument in harmony with the sentiments of an
assassin." — Ambrose Bierce.
accumulator Computers. A register or electric circuit in a calculator or computer, in which the results of arithmetical and logical operations are formed.
[AHD]
ACM (Academy of Country Music) "Improving lives by connecting fans, artists and the industry." [from website]
Acousta-Voicette™Equalizers. Altec Lansing trademarked name for their model 729A graphic equalizer, a two channel, 24-band, cut-only1/3-octave design introduced in 1971. This was the first commercially available 1/3-octave graphic equalizer.
acoustic calculators Incredible web guide to online acoustic conversion calculators.
acoustic cryptanalysisThe science of deciphering intelligence from secondary sounds emitted by computers and peripherals. [Fascinating field; hit the link to explore further.]
acoustic diodeAn apparatus that transmits sound in only one direction. First use is in medical ultrasound imaging equipment.
acoustic distortion Term coined by Dr. Peter D'Antonio, founder
of RPG Diffusor Systems, for the interaction
between the room, the loudspeaker, and the listener.
acoustic feedback The phenomenon
where the sound from a loudspeaker is picked up by the microphone feeding
it, and re-amplified out the same loudspeaker only to return to the same
microphone to be re-amplified again, forming an acoustic loop. Each time
the signal becomes larger until the system runs away and rings or feeds back on itself producing the all-too-common scream or squeal
found in sound systems. These buildups occur at particular frequencies
called feedback frequencies.
acoustic impedance Technically it is the complex ratio of acoustic pressure to acoustic volume velocity, at a single frequency. Equivalently, it is a frequency response function in which pressure is the output and volume velocity is the input. [Morfey] First described by Webster in 1919.
acoustic lens 1.Loudspeakers. An acoustic lens focuses sound in much the same way that an optical
lens focuses light. Snell's law describes
the refraction of sound as it passes
through an interface between two materials of differing sound speed. A
high frequency loudspeaker mechanical acoustic lens provides the appropriate
apparatus to spread a single point sound source into a parallel wave front.
Additional information available from JBL.
2. Ultrasonography. A lens
(often electromagnetic) used to focus or diverge a sound beam.
acousticsHearing; from the Greek akouein: to hear. The study of sound.
1. Of or relating to sound, the sense of hearing, or the science of sound. 2.
a. Designed to carry sound or to aid in hearing. b. Designed to absorb or control sound: acoustic tile. 3. Music a. Of or being an instrument that does not produce or enhance sound electronically: an acoustic guitar; an acoustic bass. b. Being a performance that features such instruments: opened the show with an acoustic set. [AHD]
acoustic treatments There are
only three classic (physical) tools available for the acoustician to treat
a room: absorbers, reflectors and diffusers. Absorbers attenuated sound;
reflectors redirect sound, and diffusers (hopefully) uniformly distribute
sound. Or put another way, these tools change the temporal, spectra and spatial qualities of the sound. Additionally, with today's advanced digital audio
tools, all of these elements can be electronically manipulated.
AC power plugs and sockets Electrical Power. The various plugs and sockets used to connect any country's AC mains and appliances and other electrical equipment. Hit the link to see all the variations and details.
acquisition time The time required for a sample-and-hold (S/H)
circuit to capture an input analog value; specifically, the time for the
S/H output to approximately equal its input.
ACR (attenuation to crosstalk ratio) Category
wiring. The ratio of attenuation and crosstalk in a cable, i.e.,
a measure of the difference between the received signal magnitude vs. the
leaked crosstalk signal.
acronym A word formed from the first letters of a name, such as laser for light amplification by stimulated emission
of radiation, or by combining initial letters or parts of a series
of words, such as radar for radio detecting and ranging. The requirement of forming a word is what distinguishes
an acronym from an abbreviation (or initialism as it is also called).
Thus modem [modulator-demodulator] is an acronym,
and AES [Audio Engineering Society] is an abbreviation
or initialism. Compare with portmanteau
word [Unsubstantiated rumor has it that the word "acronym" itself is
an acronym, created from the phrase "abbreviating by cropping remainders off names to yield meaning"
— but it has never been confirmed.] (Thanks MR.)
AC tape bias Tape Recorders. First applied by Dr. Walter Weber at Siemens in the early '40s to ferric-oxide tapes base on previous work in the '20s used on wire recorders.
active component Electronics. A component requiring power to operate, e.g. a transistor. Contrast with passive.
active crossfader A device found
in DJ mixers used to crossfade between
two music sources. An active design uses the potentiometer to send a control
voltage to some type of voltage-controlled device that controls the audio,
while in a passive design the audio appears on the potentiometer itself.
Active designs are more robust and offer greater reliability over passive
ones. See Evolution of the DJ Mixer Crossfader by Rane's ace DJ mixer designer, Rick Jeffs, for additional details.
active crossover A loudspeaker crossover requiring a power supply to
operate. Usually rack-mounted as a separate unit, active crossovers require
individual power amplifiers for each output frequency band. Available in
configurations known as stereo 2-way, mono 3-way, and so
on. A stereo 2-way crossover is a two-channel unit that divides
the incoming signal into two segments, labeled Low and High outputs (biamped). A mono 3-way unit is a single channel
device with three outputs, labeled Low, Mid and High (triamped). In this case, the user sets two frequencies:
the Low-to-Mid, and the Mid-to-High crossover points. Up to stereo 5-way configurations exist for very elaborate systems. See passive
crossover and the RaneNote Signal Processing
Fundamentals.
active equalizer A variable equalizer requiring a power supply to operate. Available in many different configurations
and designs. Favored for low cost, small size, light weight, loading indifference,
good isolation (high input and low output impedances), gain availability
(signal boosting possible), and line-driving ability. Disliked for increased
noise performance, limited dynamic range, reduced reliability, and RFI
susceptibility; however, used everywhere. See the RaneNote Operator
Adjustable Equalizers.
ActiveX A Microsoft developed software technology released in 1996. ActiveX, formerly
called OLE (Object Linking and Embedding), is loosely based on the Component
Object Model (COM), but provides substantially different services to developers.
An ActiveX component is a unit of executable code (such as an .exe file) that follows the Active X specification for providing objects.
This technology allows programmers to assemble reusable software components
into applications and services. However, component software development
using ActiveX technology should not be confused with Object-Oriented Programming
(OOP). OOP is concerned with creating objects, while ActiveX is
concerned with making objects work together. Simply stated, ActiveX
is a technology that lets a program (the ActiveX component or control)
interact with other programs over a network (e.g., the Internet), regardless
of the language in which they were written. ActiveX components can do similar
things as Java beans, but they are quite different.
Java is a programming language, while ActiveX controls can be written in
any language (e.g., Visual Basic, C, C++, even Java), Also ActiveX runs
in a variety of applications, while Java beans usually run only in Web
browsers. ActiveX controls are of concern to the pro audio community, because
this is the technology that allows designers of computer-controlled sound
systems to create common front-end software control panels that will operate
different manufacturer's units, without having to know anything about their
internal code or algorithms. Each ActiveX control is made up of properties,
values associated with the control which might include such things as level
settings and meter readings, and events, which tell the computer
something significant has happened, such as a switch closer or clip detection.
ActiveX allows the manufacturer to create an object that fully describes
a device, while hiding the implementation details, such as protocol from
the programmer. By hiding the communication details, there is no longer
a need for different manufacturer's devices to agree on protocol. This lack of a protocol standard means that cooperation between manufacturers
is not required. It allows each manufacturer to choose the best protocol
for their devices.
ACU (Audio Coverage Uniformity) A standard issued by InfoComm performance standards program. Read overview here.
adaptive delta modulation (ADM) A variation of delta
modulation in which the step size may vary from sample to sample.
ADAT (Alesis Digital Audio Tape) Digital tape recording system developed by
Alesis, and since licensed to Fostex & Panasonic, putting 8-tracks
of 16-bit, 44.1 kHz digital audio on S-VHS tape.
ADAT ODI (optical digital interface) See ADAT Optical.
ADAT OpticalAlesis's proprietary multichannel optical (fiber optic) digital interface specification
for their family of ADAT modular digital multitrack recorders. This standard
describes transmission of 8-channels of digital audio data through a single
fiber optic cable.
ADC (or A/D, analog-to-digital
converter) The electronic component which converts the instantaneous
value of an analog input signal to a digital word (represented as a binary
number) for digital signal processing. The ADC is the first link in the
digital chain of signal processing. See data
converter bits See the RaneNote Digital Dharma
of Audio A/D Converters.
ade (Amsterdam Dance Event) International 5-day conference and festival for electronic music.
ADJA (American Disc Jockey
Association) An organization of professional disc jockeys that
promotes ethical behavior, industry standards and continuing education
for its members.
admittance Electronics. The reciprocal
of impedance.
ADPCM (adaptive differential pulse code modulation) A very fast data compression algorithm based on the differences occurring
between two samples.
ADR (automatic dialog replacement) Film postproduction
term used to indicate the act and location where dialogue that is not taped
during production or that needs to be redone is recorded and synchronized
to the picture. Usually the name of the room where this occurs, containing
a studio with a screen, TV monitors, microphones, control area, console
and loudspeakers.
AEC (acoustic echo cancellation) A technique using DSP (analog circuits exist, but DSP solutions are overwhelmingly superior) that filters unwanted signals caused by echoes from the main audio source. Echoes happen in both voice and data conversation, therefore two types of cancellers are encountered: acoustic and line. "Acoustic" echo cancellers are used in teleconferencing applications to suppress the acoustic echoes caused by the microphone/loudspeaker combination at one end picking up the signal from the other end and returning it to the original end. It is similar to sound system feedback problems (where the sound reinforcement loudspeaker is picked up by the microphone, re-amplified through the loudspeaker, only to be picked up again by the microphone, to be re-amplified, and so on), only made much worse by the additional time delay introduced by the telecommunication link. "Line" echo cancellers are used to suppress electrical echoes caused by the transmission link itself. Such things as non-perfect hybrids, and satellite systems (creating round-trip delays of about 600 ms), contribute to very annoying and disruptive line echoes.
Aeolian tones Air passing over an object produces a sound called Aeolian sound or tone after the Greek god of the winds, Aeolus.
Aeolus Muscial Instrument. A stringed horn instrument created by artist Luke Jerram that resembles a giant hedgehog.
aerophone Term for a musical instrument that produces its sound by using air as the primary vibrating agent; aerophones form one of the four main classes of instruments. [Sadie] See: chordophone, idiophone, membranophone.
AES (Audio
Engineering Society) Founded in 1948, the largest professional
organization for electronic engineers and all others actively involved
in audio engineering. Primarily concerned with education and standardization.
AES2 The standard for loudspeaker testing, officially known as AES2 AES standard for acoustics - Methods of measuring and specifying the performance of loudspeakers for professional applications - Drive units.
AES3 interface(The interface formerly
known as AES/EBU). The serial transmission format standardized for
professional digital audio signals (AES3AES Recommended Practice for Digital Audio Engineering - Serial transmission
format for two-channel linearly represented digital audio data). A
specification using time division multiplex for data, and balanced
line drivers to transmit two channels of digital audio data on a single
twisted-pair cable using 3-pin (XLR) connectors. Issued as ANSI S4.40-1985
by the American National Standards Institute. In addition, information
document AES-3id is available describing the transmission of AES3 formatted
data by unbalanced coaxial cable. Transmission by fiber optic cable is
under discussion. The consumer version is referred to as S/PDIF.
See the RaneNote Interfacing AES3 and S/PDIF. [Usage Note for AC-3 and DTS Transmission: The question comes up of whether a unit that passes AES3 will automatically pass AC-3 and DTS. Two industry experts answer "maybe" as follows:
Tom Holman warns: " 'Automatically' is the operative word here. You have to pass all the bits unaltered and it will work. We have found things with hidden embedded sample rate converters set to 1:1 conversion that changed bits and thus cause AC-3 bit streams to fail for instance. DC blockage filters in DSP code do it, anything that alters the bit stream can do it. It took a very long time to develop a bit identical path through a production chain to make our test CDs, available from Hollywood Edge. We applied a Prism Sound bit test pattern signal as a track, and it failed at nearly every stage but one in getting from computer to DAT to CD-R to workstation to CD-R to mastering station to CD replication plant. Those steps all failed initially, but the one that didn't is the one all the musicians suspect: the actual manufacturing of the discs was a perfect replication of the bits sent them. Nobody owns the trademark Digital, thus it can be genius or junk. Hard to tell which some times."
And Rich Cabot elaborates: "There are several issues about how hardware operates that will affect whether it passes AC-3. These interact with the design of the AC-3 decoder.
First, any buffer/storage device which uses a sample rate converter to eliminate jitter on the received signal would pass PCM but completely screw up any coded audio. There are many receiver chips with built in SRCs. Assuming this is not the problem, there are some more subtle issues that must be considered.
There are several flavors of AC-3 over AES/SPDIF (they are described in IEC-61937). The consumer version, which is the most common, puts the AC-3 signal in both channels of the SPDIF. The professional formats allow this two channel packing but also allow AC-3 in either channel and PCM in the other. All three versions pack the AC-3 as 16 bit words so they can pass through consumer interfaces that might not pass all 24 bits.
In all versions, the interface status bits are supposed to indicate that it is a coded signal. Also, the validity bit has been hijacked and now indicates that it is a coded signal.
If someone builds a device that passes the audio bits but changes status bits and/or the validity bit there could be problems. The decoder design affects what happens. Many decoders do not attempt to decode the signal unless both the validity bits and the status bits indicate that it is coded. Others will decode regardless of the status bit content but still look at the validity bits. I don't know for sure, but some may ignore both status and validity information and only look at the stream.
In applications where one interface channel contains PCM and the other contains coded audio the status and validity bits for each channel must be set independently to reflect what the channel is carrying. The decoder is supposed to monitor the channels independently and adjust appropriately. To my knowledge consumer decoders do not do this and there are no consumer devices which produce these split channel formats. However, professional decoders do and some professional installations do carry a linear version of the signal in one channel to simplify monitoring and identification.
If a buffer/storage device read only one channel of status bits and reproduced them in both output channels it would cause problems with these professional applications. If the buffer/storage device read only one validity bit or combined the two channels of validity bits it would also cause problems.
If the product is a simple analog/digital buffer to TOSLINK device I don't see why it wouldn't pass AC-3. However, if the receiver does any reclocking of the signal it would not. Also, if they use a different optical interface that packs the bits into a synchronous optical fiber link might would not pass AC-3, depending on the status/validity bit handling."]
AES3-MIC Any microphone having a digital output that conforms to AES42 AES standard for acoustics - Digital interface for microphones.
AES17 low-pass filter The common name given to the low-pass filter
defined by AES17 AES standard method for digital audio engineering — Measurement of digital
audio equipment, used to limit the measuring bandwidth. The rather
daunting specification calls for a filter with a passband response of 10 Hz to 20 kHz, ±0.1 dB and a stopband attenuation greater than 60 dB at 24 kHz.
AES48 This the standard on proper shield grounding, specifically AES48 AES standard on interconnections - Grounding and EMC practices - Shields of connectors in audio equipment containing active circuitry.
AES50 This open standard defines a Layer 1 protocol using Ethernet wiring, albeit not a true switched audio network. Titled: AES50 AES standard for digital audio engineering - High-resolution multi-channel audio interconnection (HRMAI).
AES67 The standard for operating pro audio network systems in an interoperable manner, specifically AES67 AES standard for audio applications of networks - High-performance streaming audio-over-IP interoperability.
AFL Abbreviation for after fade listen,
a term used on recording consoles and mixers,
referring to a signal taken after the main channel fader; hence this sampling
point tracks the main fader level. Also referred to as post fade solo,
but since PFL already meant pre fade, AFL was adopted to prevent
confusion. Got it? Compare with PFL and APL.
AGC (automatic gain control), aka ALC (automatic level control) Signal
Processing. A circuit or algorithm that varies gain as a function
of the input signal amplitude. Commonly found in pro audio applications
where you want to automatically adjust the gain of different sound sources
in order to maintain a constant loudness level at the output. For example,
on deluxe professional DJ mixers the gain adjusts automatically when the
DJ switches sources between records, CD, or MP3 files. Not only do signal
levels differ greatly between different source technologies but also between
any two examples of the same technology, e.g., between CDs, or between
MP3 files, etc.
AIA (American Institute of Architects) The premier organization for architects and those working with architects (sound contractors, integrators, etc.).
AIFF (audio interchange file format) Defined by Apple Computer in
1988, it provides a standard for storing monaural and multichannel sampled
sounds at a variety of sample rates and widths.
A LawTelecommunications. The PCM coding and companding standard used in Europe and in areas outside of North American influence. [Newton] Contrast with Mu Law used in North America and Japan.
aleatoric Music. Using or consisting of sounds to be chosen
by the performer or left to chance; indeterminate. From aleatory meaning dependent on chance, luck, or an uncertain outcome. Of or characterized
by gambling. [AHD]
algorithm A structured set of instructions
and operations tailored to accomplish a signal processing task. For example,
a fast Fourier transform (FFT), or a finite
impulse response (FIR) filter are common DSP algorithms.
algorithmic reverb Audio Signal Processing. Digital simulation of reverberation based on algorithms. Contrast with convolution reverb.
Allison Effect Loudspeakers & Acoustics. Describes
how room boundaries and loudspeaker power output interact. Specifically,
the name for the destructive interference pattern that develops when a
radiator is located one-quarter wavelength away from a reflective surface;
after Roy F. Allison, American acoustic engineer of AR (Acoustic Research) and Allison Acoustics fame, who first wrote of this effect in his paper, "The Influence of Room Boundaries on Loudspeaker Power Output," J. Aud. Eng. Soc. Vol.
22, p.314 (May 1974), reprinted in Loudspeakers
Vol. I, pp.339-345, edited by R.E. Cooke (Audio Engineering Society, 1978).
Allison, Roy (1927-2016) American acoustic engineer noted for his contributions to early loudspeaker design. See above for one example.
all-pass filterA filter that provides
only phase shift or phase delay without appreciably changing the magnitude
characteristic.
ALMA (American Loudspeaker Manufacturers Association) Founded in
1964, an international trade association for companies that design, manufacture,
sell, and/or test loudspeakers, loudspeaker components and loudspeaker
systems.
alnico (al[uminum] + ni[ckle] + co[balt] ) Magnetics. Any of several hard, strong alloys of iron, aluminum, nickel, cobalt and sometimes copper, niobium, or tantalum, used to make strong permanent magnets [found in loudspeakers]. [AHD]
ALS (assisted listening systems) Hearing. See: hearing loop for one example.
alternating current Abbr. AC or ac (See usage note at end) An electric current that reverses direction at regularly recurring intervals of time. Contrast: direct current. [IEEE] [Usage Note: Officially the IEEE dictionary is very clear that the abbreviation for alternating current is "ac" not "AC." However most everyone agrees (mags, technical journalists, me, etc.) that when abbreviating alternating current in a standalone sense, that it looks better and reads clearer if you use uppercase, e.g., "The device runs off AC voltage," instead of "The device runs off ac voltage,", particularly if the abbreviation begins or ends a sentence. Imagine a sentence like this: "Ac is a type of generator voltage." Or, "Do you want ac or dc?" Both work better with uppercase. As for Vac vs. VAC, both are seen and accepted even though Vac is the IEEE standard.]
aluminum sheath Wiring & Cable. An impervious aluminum or aluminum alloy tube, either smooth or corrugated, which is applied over a cable core to provide mechanical protection. [IEEE]
AM (amplitude modulation) Radio broadcast. 1. The encoding of a carrier wave by variation of its amplitude in accordance with an input signal. 2. A broadcast system that uses amplitude modulation. [AHD]
ambience 1. Acoustics. A perceptual
sense of space [Blesser]. The acoustic
qualities of a listening space [White].
2. Psychoacoustics The special atmosphere or mood created by a particular
environment; also spelled ambiance [AHD].
Contrast with reverberation.
ambient The medium (for example, air, gas, liquid, or earth) in which electric equipment operates. [IEEE]
Ambisonics A British-developed surround sound system designed to reproduce a true three-dimensional sound field. Based on the late Michael Gerzon's (1945-1996) (Oxford University) famous theoretical foundations, Ambisonics delivers what the ill-fated quadraphonics of the '70s promised but could
not. Requiring two or more transmission channels (encoded inputs) and four
or more decoded output loudspeakers, it is not a simple system; nor is
the problem of reproducing 3-dimensional sound. Yet with only an encoded
stereo input pair and just four decoded reproducing channels, Ambisonics
accurately reproduces a complete 360-degree horizontal sound field
around the listener. With the addition of more input channels and more
reproducing loudspeakers, it can develop a true spherical listening shell.
As good as it is, a mass market for Ambisonics has never developed due
to several factors. First, the actual recording requires a special tetrahedron array of four microphones: three to measure left-right, front-back and
up-down sound pressure levels, while the fourth measures the overall pressure
level. All these microphones must occupy the same point in space as much
as possible. So far, only one manufacturer (first Calrec, bought by AMS,
bought by Siemens, sold, now Soundfield)
is known to make such an array. Next, a professional Ambisonics encoding
unit is required to matrix these four mic signals together to form two
or more channels before mastering or broadcast begins. Finally, the consumer
must have an Ambisonics decoder, in addition to at least four channels
of playback equipment. [The generic term is now soundfield microphone recording .]
AME (Association for Manufacturing Excellence) "A not-for-profit organization founded in 1985 dedicated to helping companies with continuous improvement and their pursuit of excellence."
Americana Music Festival Yearly event held in Nashville, TN, since 2000, featuring over 150 performances at over nine venues, spread out over four days.
AMI-C (Automotive Multimedia
Interface Collaboration) "An organization of motor vehicle manufacturers
worldwide created to facilitate the development, promotion and standardization
of electronic gateways to connect automotive multimedia, telematics and
other electronic devices to their motor vehicles."
AMOLED (active-matrix OLED) Electronic Displays. Refers to the technology behind the addressing of pixels in OLED displays.
AMP (Audio Music Partnership) An alliance of industry partners that develop, manufacture, and support products and services that interoperate with the Microsoft platforms.
AMP (Association of Music Parents) A non-profit organization that promotes music education in school systems.
ampacity (ampere capacity) The maximum current-caring capacity of a material. [This is an example of a portmanteau word.]
AMPAS (Academy of Motion
Picture Arts & Sciences) Created in 1927, a professional honorary
organization composed of over 6,000 motion picture craftsmen and women. Think Oscars®.
ampere Abbr. I, also A. 1. A unit of electric current in the International standard meter-kilogram-second (mks) system. It is the steady current that when flowing in straight parallel wires of infinite length and negligible cross section, separated by a distance of one meter in free space, produces a force between the wires of 2E-7 newtons per meter of length.2. A unit in the International System
specified as one International coulomb per second and equal to 0.999835
ampere. (After André MarieAmpère.) [AHD]
Ampère, André Marie (1775-1836) French physicist
and mathematician who formulated Ampère's law, a mathematical description
of the magnetic field produced by a current-carrying conductor. [AHD]
amplifier An electronic device used to
increase an electrical signal. The signal may be voltage, current or both (power). Preamplifier is the name applied to the first amplifier in
the audio chain, accepting inputs from microphones,
or other transducers, and low output
sources (CD players, tape recorders, turntables, etc.). The preamplifier
increases the input signals from mic-level,
for instance, to line-level. Power
amplifier is the name applied to the last amplifier in the audio
chain, used to increase the line-level signals to whatever is necessary
to drive the loudspeakers to the loudness required. See amplifier classes.
amplifier classes Audio power
amplifiers were originally classified according to the relationship between
the output voltage swing and the input voltage swing; thus it was primarily
the design of the output stage that defined each class. Classification
was based on the amount of time the output devices operate during one complete
cycle of signal swing. Classes were also defined in terms of output
bias current [the amount of current flowing in the output devices with
no applied signal]. For discussion purposes (with the exception of class
A), assume a simple output stage consisting of two complementary devices
(one positive polarity and one negative polarity) using tubes (valves)
or any type of transistor (bipolar, MOSFET, JFET, IGFET, IGBT, etc.).
[Historical Notes marked "GRS" provided by Gerald R. Stanley,
Senior V.P. of Research, Crown International,
Inc., designer of the famous Crown DC-300, inventor of the Crown K
Series switchmode amplifier line and holder of over 45 U.S. Patents.]
[GRS on amplifiers: "At first there were no amplifiers as the very
thought of amplification had yet to enter the vocabulary of electronics
(another word which had yet to be birthed!). The invention of a three-terminaled
device (DeForest Audion U.S. patent 841,386 or later triode) was the invention
in 1906 of a more sensitive radio detector and not an element for an amplifier.
By 1912 the triode had become both a vacuum tube and an amplifier
(multiple names can be attached to this collective achievement). The oscillator
also dates to 1912 giving proof to the saying "When you set out to make
an amplifier you get an oscillator and when you attempt to make an oscillator
you get an amplifier."]
[GRS on amplifier classes: "Originally it was adequate to distinguish
amplifier classes only by the conduction angles of the control elements
(tubes or valves). More recently it has been necessary to add distinctions
that relate to topology, degrees of conduction and control methods to be
able to determine class."]
Class A operation is where both devices conduct
continuously for the entire cycle of signal swing, or the bias current
flows in the output devices at all times. The key ingredient of class A
operation is that both devices are always on. There is no condition where
one or the other is turned off. Because of this, class A amplifiers in
reality are not complementary designs. They are single-ended designs with
only one type polarity output devices. They may have "bottom side" transistors
but these are operated as fixed current sources, not amplifying devices.
Consequently class A is the most inefficient of all power amplifier designs,
averaging only around 20% (meaning you draw about 5 times as much power
from the source as you deliver to the load.) Thus class A amplifiers are
large, heavy and run very hot. All this is due to the amplifier constantly
operating at full power. The positive effect of all this is that class
A designs are inherently the most linear, with the least amount of distortion.
[Much mystique and confusion surrounds the term class A. Many mistakenly
think it means circuitry comprised of discrete components (as opposed to
integrated circuits). Such is not the case. A great many integrated circuits
incorporate class A designs, while just as many discrete component circuits
do not use class A designs.]
[GRS Historical Note: "Class A - The most basic of operating
modes saw both single-ended and push-pull embodiments by 1913. The first
known use of push-pull appears in a patent of E.F.W. Alexanderson of GE
U.S. 1,173,079 filed in 1913. While Alexanderson would have been aware
of other levels of biasing his push-pull stage, such as classes B and C,
he would have only been able to produce a useful result with a tuned stage
such as a transmitter where resonant filtering would have managed the distortion
problem. Negative feedback is not understood in 1913 to be able to cope
with distortion problems."]
Class B operation is the opposite of class A. Both output devices
are never allowed to be on at the same time, or the bias is set so that
current flow in a specific output device is zero when not stimulated with
an input signal, i.e., the current in a specific output flows for one half
cycle. Thus each output device is on for exactly one half of a complete
sinusoidal signal cycle. Due to this operation, class B designs show high
efficiency but poor linearity around the crossover region. This is due
to the time it takes to turn one device off and the other device on, which
translates into extreme crossover distortion. Thus restricting class B
designs to power consumption critical applications, e.g., battery operated
equipment, such as 2-way radio and other communications audio.
[GRS Historical Note: "Class B - This class has no obvious
inventor, but it does have its master and perfector. Loy
Barton working for RCA developed tube designs and biasing methods to
manage the open loop distortion of class B push-pull power stages. His
IRE paper in 1931 titled "High Output Power from Relatively Small Tubes"
is a landmark in the history of class B. Technically he only used class
AB but the distinction was not in the language. Class AB is a later and
probably unnecessary class fabrication."]
Class AB operation is the intermediate case.
Here both devices are allowed to be on at the same time (like in class
A), but just barely. The output bias is set so that current flows in a
specific output device appreciably more than a half cycle but less than
the entire cycle. That is, only a small amount of current is allowed to
flow through both devices, unlike the complete load current of class A
designs, but enough to keep each device operating so they respond instantly
to input voltage demand s. Thus the inherent non-linearity of class B designs
is eliminated, without the gross inefficiencies of the class A design.
It is this combination of good efficiency (around 50%) with excellent linearity
that makes class AB the most popular audio amplifier design.
Class AB1 & AB2 Subdivisions of Class AB developed for vacuum
tube design. These subsets primarily describe grid current behavior: Class
AB1 has no current flowing into the grid of the tube, and Class AB2 has
some current flowing into the grid. Class AB1 operates closer to Class
A, while Class AB2 operates closer to Class B. Most bipolar solid-state
amplifiers would be classified as Class AB2, while power JFET designs mimic
Class AB1.
Class AB plus B design involves two
pairs of output devices: one pair operates class AB while the other (slave)
pair operates class B.
[GRS Historical Note: "Class AB+B is a term that I'd coined
and is intended to be very descriptive but is not truly worthy of its own
class. The Crown DC-300 was the first to use this mode of operation in
1968."]
Class BD Invented by Robert B. Herbert in
1971 U.S. patent 3,585,517 and improved on by Neil Edward Walker as disclosed
in his 1971 U.S. patent 3,629,616. Both patents are concerned with improving
original class D design efficiencies by using various bridge connections
and cancellation techniques. And most recently more improvements are claimed
by inventors James C. Strickland & Carlos A. Castrejon in their U.S.
patent 6,097,249 assigned to Rockford
Corporation in 2000 for their Fosgate-brand automotive amplifier.
[GRS comments: "This is a class designation that would best
be forgotten. It has been applied to multiple modulation schemes on a class
D derived full-bridge. This is perhaps the most reinvented class design
in recent history with "filter-less amplifiers" and other such things.
An interleave of two class D full-bridge is what we actually have here,
and it is a good improvement to an interleave of one class D full-bridge.
However an interleave of four is actually possible on a full-bridge if
one uses Class I design."]
Class C use is restricted to the broadcast industry for radio frequency
(RF) transmission. Its operation is characterized by turning on one device
at a time for less than one half cycle. In essence, each output device
is pulsed-on for some percentage of the half cycle, instead of operating
continuously for the entire half cycle. This makes for an extremely efficient
design capable of enormous output power. It is the magic of RF tuned circuits
(flywheel effect) that overcomes the distortion create d by class C pulsed
operation.
Class D operation is switching, hence the
term switching power amplifier. Here the output devices are rapidly
switched on and off at least twice for each cycle (Sampling
Theorem). Theoretically since the output devices are either completely
on or completely off they do not dissipate any power. If a device is on
there is a large amount of current flowing through it, but all the voltage
is across the load, so the power dissipated by the device is zero (found
by multiplying the voltage across the device [zero] times the current
flowing through the device [big], so 0 x big = 0); and when the
device is off, the voltage is large, but the current is zero so you get
the same answer. Consequently class D operation is theoretically 100% efficient,
but this requires zero on-impedance switches with infinitely fast switching
times — a product we're still waiting for; meanwhile designs do exist
with true efficiencies approaching 90%.
[Historical note: the original use of the term "Class D"
referred to switching amplifiers that employed a resonant circuit at the
output to remove the harmonics of the switching frequency. Today's use
is much closer to the original "Class S" designs.]
[GRS Historical Note: "Class D is a subset of all possible switch-mode
amplifier topologies that is typified by use of the half-bridge (totem-pole)
output stage that has two interconnected switches operating in time alternation.
The paradigm is that of Loy Barton's class B, but uses the statistics of
conduction angle to produce amplification (PWM).
There are many subclasses within class D that describe the origins of the
modulation. Class D is at least as old as 1954 when Bright patented a solid-state
full-bridge servo amplifier U.S. 2,821,639."]
Class E operation involves amplifiers designed for rectangular input
pulses, not sinusoidal audio waveforms. The output load is a tuned circuit,
with the output voltage resembling a damped single pulse. Normally Class
E employs a single transistor driven to act as a switch.
The following terms, while generally agreed upon, are not official
classifications:
Class F Also known by such terms as "biharmonic,"
"polyharmonic," "Class DC," "single-ended Class D," "High-efficiency Class
C," and "multiresonator." Another example of a tuned power amplifier, whereby
the load is a tuned resonant circuit. One of the differences here is the
circuit is tuned for one or more harmonic frequencies as well as the carrier
frequency. See References Krauss, et al. for complete details.
[GRS Historical Note: "Classes E and F are distinguished
by their resonant topology and not conduction angle else we would class
them with C. A good reference to these is found in the many patents of
Nathan Sokal. Also class S, which is very old (1929-1930), has similar applications
(resonant RF)."]
Class G operation involves changing the power
supply voltage from a lower level to a higher level when larger output
swings are required. There have been several ways to do this. The simplest
involves a single class AB output stage that is connected to two power
supply rails by a diode, or a transistor switch. The design is such that
for most musical program material, the output stage is connected to the
lower supply voltage, and automatically switches to the higher rails for
large signal peaks [thus the nickname rail-switcher]. Another approach
uses two class AB output stages, each connected to a different power supply
voltage, with the magnitude of the input signal determining the signal
path. Using two power supplies improves efficiency enough to allow significantly
more power for a given size and weight. Class G is common for pro audio
designs.
[Historical note: Hitachi is credited with popularizing
class G designs with their 1977 Dynaharmony HMA 8300 power amplifier, however
it is shown much older by GRS: "Class G - I have been searching for the
proper inventor of this class, but have not been able to find a reference
older than 1965 when I first encountered it in a college text "Handbook
of Basic Transistor Circuits and Measurements" by Thornton et al., SEEC
vol. 7. The method is introduced without references or fanfare. One is
led to believe that it was common knowledge in 1965 and earlier. This is
not the first known use of extended quasi-linear methods (beyond class
B), as there is a dual found in Fisher U.S. 2,379,513 from 1942."]
Class H operation takes the class G design
one step further and actually modulates the higher power supply voltage
by the input signal. This allows the power supply to track the audio input
and provide just enough voltage for optimum operation of the output devices
[thus the nickname rail-tracker or tracking power amplifier].
The efficiency of class H is comparable to class G designs.
[Historical note: Soundcraftsmen is credited with popularizing class H designs with their 1977 Vari-proportional MA5002 power amplifier, designed by Soundcraftsmen's Chief Engineer and Vice President, Paul Rolfes.
However like class G above, GRS finds precedence: "Class H - The apparent
inventor of class-H in full-blown multi-level form was Manuel Kramer of
NASA in 1964 U.S. patent 3,319,175. Class H optimally applied to a full-bridge
was invented in 1987 (Stanley) U.S. 4,788,452. Classes G and H are all
members of a class of amplifiers that has articulated rail voltages to
improve the efficiency of class B power stages. Examples are available
of tracking using binarily weighted segments, (Stanley) U.S. 5,045,990.
Continuously variable tracking with switch-mode PWM appears to have been first done by Hamada in 1976 U.S. 4,054,843. The ultimate
rail tracker using interleaved technology is found in (Stanley) U.S. 5,513,094.
Only with interleave is the converter fast enough to meet the needs of
full-bandwidth audio and yet have low switching losses."]
Class I operation invented and named by Gerald
R. Stanley for amplifiers based on his patent U.S. 5,657,219 covering opposed
current converters.
[GRS explains: The "I" of the class is short for "interleave"
as this is the only four-quadrant converter known that uses two switches
yet has an interleave number of 2 in the terminology of interleave. When
used with fixed-frequency natural two-sided PWM it forms a theoretically
optimum converter having the least unnecessary/undesirable PWM spectra.
A good reference is found in the IEEE Transactions on Power Electronics
Vol. 14, No. 2, March 1999, pages 372-380."]
Class J operation is the category/name suggested
by Gerald R. Stanley for amplifiers that combine class B and class D where
converters act in parallel to drive the load.
[GRS elaborates: "There are serious problems with the power efficiency of these products when processing fast signals into arbitrary
loads. The class B stage is used to actively remove the ripple of the class
D stage and other distortion problems that plague class D. No solution
is offered for the MOSFET CSOA (current
safe operating area) problem of class D. To solve that problem it would
be necessary to parallel a class I and class B amplifier but this would
be without merit as the class I amplifier generally does not need the class
B amplifier to meet fidelity requirements."]
Class S First invented in 1932, this technique
is used for both amplification and amplitude modulation. Similar to Class
D except the rectangular PWM voltage waveform is applied to a low-pass
filter that allows only the slowly varying dc or average voltage component
to appear across the load. Essentially this is what is termed "Class D" today. See References Krauss for details.
[Final GRS Amplifier Historical Note:
"All of our amplifier classes have thrived under a very important invention,
without which most would have floundered. That invention is, of course,
negative feedback. Harold Black in
1927 changed our world forever while riding to work on the Lackawanna Ferry.
(See U.S. patent 2,102,671.) Harold Black did not stop there however, he
also in 1953 wrote the text "Modulation Theory" which we today use to understand the fundamentals of PWM. In 1935, Terman, in his now famous "Fundamentals
of Radio" handbook, wrote that it was good that class B was only used in
places like radio stations as there needed to be an engineer on duty full
time to keep the bias tweaked to where the distortion was acceptable. Thanks
go to Harold Black for changing all that and leading us into the next century
of amplification."]
amplifier dummy load Modeling a real
world loudspeaker for power amplifier testing purposes has been studied
for years, resulting in many circuit possibilities. An article compiled
and edited by Tomi Engdahl entitled "Speaker
Impedance" is an excellent summary of the results. He gives a complete
(and complex) solution to the loudspeaker dummy load question. However
you can get excellent results with a simplified version developed by electronics engineer Michael Rollins appearing below. The series resistor and inductor model the loudspeaker voice coil's DC resistance and inductance, while the parallel inductor and capacitor simulate the mechanical components of suspension compliance and cone mass respectively. The values shown work well for most power amplifier measurements.
RS = 6 ohms (aluminum body
power resistor bolted to a heat sink; power rating twice max testing watts)
LS = 0.33 mH (air core inductor; wire sized for max current)
LP = 20 mH (air core inductor; wire sized for max current)
CP = 1000 µF (100 V, or maximum expected peak voltage;
paralleling two 500 µF caps may be smaller, cheaper)
amplitude 1. Greatness of size; magnitude.
2. Physics. The maximum absolute value of a periodically varying
quantity. 3. Mathematics. a. The maximum absolute value of a periodic
curve measured along its vertical axis. b. The angle made with the positive
horizontal axis by the vector representation
of a complex number.4. Electronics. The maximum absolute
value reached by a voltage or current waveform. [AHD]
anagram A word or phrase formed by reordering the letters of another word or phrase, such as satin to stain. [AHD]
analog A real world physical quantity or
data characterized by being continuously variable (rather than making discrete
jumps), and can be as precise as the available measuring technique.
ANC (ambient noise compensator) A signal processing circuit that monitors the ambient noise in a space and adjusts the level of the amplified program material as necessary to maintain a desired signal-to-noise ratio. [Different than ANR]
AND Computer Science & Logic. A Boolean logical operator that returns
a true value only if both operands are true; a form of multiplication.
For example, two series connected switches, A and B, requires both be closed
for current to pass, thus it requires switch A AND switch B closed to operate.
anechoic Literally, without echo,
used to describe specially designed rooms, anechoic chambers, built
to emulate a free sound field, by absorbing
practically all the sound field.
anisotropic Physics. 1. Not isotropic. 2. Having properties that
differ according to the direction of measurement. [AHD]
annealed 1. To subject (glass or metal)
to a process of heating and slow cooling in order to toughen and reduce
brittleness.
2. To strengthen or harden. [AHD]
anode 1. A positively charged electrode.
2. In a vacuum tube, it is the plate
electrode. 3. In a forward-biased semiconductor diode it is the positive
terminal. Contrast with cathode.
ANR (ambient noise reduction) Any of various DSP algorithms that reduce unwanted background noise, for example, HVAC noise. A common signal processing block found in acoustic echo cancellers. [Different than ANC]
ANSI (pronounced "ann-see") (American National Standards Institute) A private organization that develops and publishes standards for voluntary
use in the U.S.A.
Antheil,
George (1900-1959) US Composer, specializing in film music, who
described himself as "America's bad boy of music."
Among Antheil's early avant-garde pieces, none caused a
greater sensation than his Balet mécanique, scored for automobile
horns, airplane propeller, fire siren, ten grand pianos, and other instruments.
When it was performed at Carnegie Hall in 1924, a concertgoer near the
orchestra could stand no more than a few minutes of the racket. Tying his
handkerchief to his cane, he raised the white flag in surrender. [Bartlett's
Book of Anecdotes]
anti-aliasing filter A low-pass filter used at the input of digital audio converters to attenuate frequencies
above the half-sampling frequency to prevent aliasing.
anti-imaging filter A low-pass filter
used at the output of digital audio converters to attenuate frequencies
above the half-sampling frequency to eliminate image spectra present at
multiples of the sampling frequency.
antiquing Digital Audio. "The act of processing modern audio files to make them appear to have originated from historic technology. It is the inverse of restoring old recordings." From the abstract.
antiskating also anti-skating Turntables. A control mechanism on a phonograph designed to compensate for the
natural tendency of a pivoted tone arm to pull toward the center. [AHD] That is, it keeps the stylus centered
in the groove.
AoE (Audio over Ethernet) Networks. Many systems exist using Ethernet for the transport of digital audio. Hit the link for details about the various proprietary protocols that include Layer 1 (e.g., Digigram's Ethersound®), Layer 2 (e.g. Cirrus Logic's CobraNet® also AVB: Audio/Video Bridging) and Layer 3 (e.g. Audinate's Dante®),
AOIP (audio over Internet Protocol) Networks. A system for audio file sharing/transport that converts analog or digital audio into Ethernet packers for distribution over a LAN or Ethernet switches.
AP (access point) Networks. A
device that connects a wireless network to a wired LAN.
APA (Audio Publishers Association) The online resource center designed for audiobook listeners and industry
professionals.
APD (auto power down) Electronics. Term used to describe equipment with a built-in feature that automatically reduces the power draw after a prescribed amount of time.
API (application
program interface) Software. Protocols for creating software
applications.
APL (after processing listen) A mixing
console term and feature that allows post-processing monitoring of the
signal. Compare with AFL and PFL.
APPA (Association of Higher Education Facilities Officers) The abbreviation, APPA, comes from their early name:
Association of Physical Plant Administrators of Universities and Colleges, which was changed in 1991. A good resource for audio contractors, integrators, etc., especially for their focus on energy efficient buildings.
apparent power The result of multiplying
the rms value of the voltage by the rms value
of the current in an electronic circuit. It is expressed in watts (W) for
resistive loads and in volt-amperes (VA) for reactive loads. It's the amount
of power the casual observer thinks is available (hence, apparent),
but because of power factor may not be — the real power is usually
less. See power factor .
appoggiatura Music. An embellishing note, usually one
step above or below the note it precedes and indicated by a small note
or special sign. [AHD] A melodic tone.
AquaSonic Name of a Danish band that performs underwater.
A&R (artists and repertory) Historically the record
industry term for the department or person that acts as the go-between
the artist and the record label. Their job is to select and sign the performers
to the label, decide what songs they will record, and select who will work
with the artists in the production arranging and performance of the material
for the recording of master tapes. These details vary a lot from label
to label. For a good discussion on how the A&R world is changing see: Wendy Day.
architecturaldrawing symbolsANSI-J-STD-710 ANSI/CEA/CEDIA/InfoComm, Audio, Video and Control Architectural Drawing Symbols. Hit the link for a free download.
arithmetic The mathematics of integers, rational numbers, real numbers, or complex numbers under addition, subtraction, multiplication, and division. [AHD]
arithmetric progression A sequence, such as the positive odd integers 1, 3, 5, 7, . . . , in which each term after the first is formed by adding a constant to the preceding term. [AHD]
ARM (advanced
RISC machines) The name for a microprocessor group formed from
Acorn, backed by Apple, VLSI Technology and Nippon Investment and Finance,
in 1990. Acorn Computer was the parent company set up by Dr. Hermann Hauser
and Dr. Chris Curry in 1979 to make personal computers, but now enjoys
its biggest success selling intellectual property around their proprietary
RISC computer, called ARM, which originally stood for Acorn RISC Machines.
armonicaMusical Instrument. Name for Benjamin Franklin's improvement on the Glass harmonic in 1761. Go to William Zeitler's website for fascinating details from one of the few modern players.
Armstrong,
Edwin Howard (1890-1954) American radio engineer and inventor of
regenerative feedback, FM (frequency modulation) and the superheterodyne
receiver.
Armstrong ParkNew Orleans site named after Louis Armstrong, considered to be the birthplace of jazz.
Arnold, H. D. American engineer who invented and patented the thermophone, while working at Western Electric. He is also credited with introducing a vacuum to the triode tube, thus perfecting its performance.
ARRL (American Radio Relay League) The
national association for amateur radio.
articulation 1. The act of vocal expression; utterance or enunciation: an articulation of the group's sentiments. 2a. The act or manner of producing a speech sound. 2b. A speech sound, especially a consonant. [AHD]
articulation index Abbr. AI Speech. A number (ranging from 0 to 1) which is a measure of the intelligibility of speech—the higher the number, the greater the intelligibility. [Harris]
artifact Audio. Anything added, due to technical limitations, that was not in the original signal.
ASA (Acoustical Society of America) Founded in 1929, the oldest
organization for scientist and professional acousticians and others engaged
in acoustical design, research and education.
ASCII (pronounced "ask-ee") (American
Standard Code for Information Interchange) An ANSI standard data transmission code consisting of seven information bits, used
to code 128 letters, numbers, and special characters. Many systems now
use an 8-bit binary code, called ASCII-8, in which 256 symbols are represented
(for example, IBM's"extended ASCII").
ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers,
Inc.) An international organization organized for the purpose of
advancing the arts and sciences of heating, ventilation, air-conditioning
and refrigeration for the public's benefit through research, standards
writing, continuing education and publications.
ASIC (application-specific integrated circuit) A large-scale
integrated circuit whose function is determined by the final mask layer
for a particular application or group of applications; for example, an
IC that does all the functions of a modem.
ASIO(pronounced "az-ee-o") (audio stream input/output) Originally a multichannel audio
transfer protocol developed by Steinberg in 1997, for audio/MIDI sequencing applications, allowing access to the
multichannel capabilities of sound cards. Today it is a standard driver protocol for digital audio and computer sound cards
ASPEC (adaptive spectral perceptual entropy coding) A
bit rate reduction standard for high quality audio. Jointly developed by
AT&T Bell Labs, Thomson, the Fraunhofer Society and CNET. Characterized
by high degrees of compression to allow audio transmission on ISDN.
asperity noise Recording. Noise caused by microscopic imperfections in the oxide coating of magnetic tape. Heard as a low frequency rumble similar to rocks banging together.
aspiration Speech. Expulsion of breath in speech. [AHD] "It occurs in the phoneme "h" in English, or with less duration after the release of an unvoiced consonant, for example, after the "p" in "pie". [Bregman]
ASTC (Association of Science-Technology Centers) "An organization of science centers and museums dedicated to furthering public engagement with science among increasingly diverse audiences." Another valuable resource for audio contractors, integrators, etc.
asymmetrical (non-reciprocal) response Term used to describe
the comparative shapes of the boost/cut curves for variable equalizers.
The cut curves do not mirror the boost curves, but instead are quite narrow,
intended to act as notch filters.
asynchronous A transmission process where the signal is transmitted
without any fixed timing relationship between one word and the next (and
the timing relationship is recovered from the data stream).
ATA (American Telemedicine Association) "The leading resource and advocate promoting access to medical care for consumers and health professionals via telecommunications technology." Another valuable resource for audio contractors, integrators, etc.
ATM (asynchronous transfer mode) networking An extremely
fast networking technology already found on many disk editors (Avid,
Sonic Solutions, Studio Audio, etc.) and predicted to infiltrate homes
within the coming decade. ATM specifies the protocol (i.e., the order and
sequence) of the digital information on the network, but not the physical
means of transmission (e.g., fiber optic, twisted-pair, etc.). The protocol
controls how the entire network is run and maintained.
Atmos®Dolby registered trademark for their 64-channel surround sound system for cinema and the companion 7.1.4 channel home system.
atmospheric pressure Pressure
caused by the weight of the atmosphere. At sea level it has a mean value
of one atmosphere but reduces with increasing altitude. [AHD]
See 0 dB-SPL.
atofaradAbbr. aF Nanotechnology. A prefix
for 10-18 farads, as in 1 ppm of a 1 pF measurement (10-6 x 10-12).
ATRAC (Adaptive Transform Acoustic Coding) Very early (1992) Sony proprietary audio data compression technique using psychoacoustic principles to convert standard CD quality audio (16-bit, 44.1 kHz) into a file one-fifth the original size.
attack Music. The beginning or manner
of beginning a piece, passage, or tone. [AHD]
A measure of how long it takes for the beginning to peak. Contrast with decay. Audio Compressors. How fast
the gain is turned down once the signal exceeds the threshold setting.
Contrast with release. Also see: automatic attack & release.
attenuator or attenuator pad Electronics.
A passive network that reduces the voltage (or power; see usage note under gain) level of a signal with negligible distortion,
but with insertion loss. Often
a purely resistive network, although any combination of inductors, resistors
and capacitors are possible, a pad may also provide impedance matching.
[Compare with fader and crossfader.
More details available in an excellent article by Rick Chinn, "Pads 101" appearing in the Syn-Aud-Con Newsletter, Vol. 32, No. 2 Spring 2004, pp. 8-11.]
Pads are referred to by the topology of the network formed,
with the two most common being an L-pad and a T-pad:
L-pad A two-leg network shaped like an inverted, backward
letter "L". It usually consists of two resistors that are fixed or adjustable.
A true variable L-pad consists of two variable potentiometers that are
ganged (tied) together. The ganged sections work to provide either a constant
input or a constant output impedance regardless of the attenuation setting.
Since modern analog audio electronic circuits consist of stages characterized
by very high input and very low output impedances, the term is now broaden
to include all L-shaped networks without the requirement of providing constant
impedance to the source or load. Volume and level controls are common examples.
Balanced L-pad (or U-pad) A balanced version of the
above L-pad, the following is for general purpose audio, recommended by
the IEC, exact and nearest 1% values shown.
T-pad A three-leg network shaped like the letter "T".
It usually consists of three resistors that are fixed or adjustable. A
true variable T-pad consists of two or three variable potentiometers that
are ganged (tied) together. The ganged sections work to provide either
a constant input or a constant output impedance regardless of the attenuation
setting. Since modern analog audio electronic circuits consist of stages
characterized by very high input and very low output impedances, the term
is now broaden to include all T-shaped networks without the requirement
of providing constant impedance to the source or load.
Bridged T-pad In this configuration, R1 and R2 are fixed to the pad's impedance, while R3 and R4 can be variable.
Balanced T-pad (or H-pad) R1 and R3 are half the values of the unbalanced
T-pad above.
O-pad Used when the input impedance is much higher than the impedance
across the output.
aubades Music. 1. A song or instrumental composition concerning, accompanying, or evoking daybreak.
2. A poem or song of or about lovers separating at dawn. [AHD]
Audimax CBS trademark for a broadcast AGC unit invented by Emil Torick in the '50s to replace the transmitter watch engineer.
audio 1. Of or relating to humanly audible sound,
i.e., audio is all the sounds that humans
hear (approximately 20 Hz - 20 kHz).2.a. Of or relating
to the broadcasting or reception of sound. b. Of or relating to high-fidelity
sound reproduction. (Audio traveling through air is vibrations,
or cycles of alternating pressure zones. Rarefaction follows each cycle of compression,
which produces a wave.) [AHD] [Usage Note: The word "audio" often refers to the electrical signal, as opposed to the acoustic meaning, which is most often referred to as "sound," rather than "audio."]
audio archaeologist A term coined by sound designer Andrew Roth to describe his specialty of capturing sounds that relate to specific time periods.
audio bridge A communications bridge that allows multiple duplex connections
over 4-wire telephone connections. Well designed audio bridges do not connect
inputs to their own outputs, thus avoiding feedback. See mix-minus.
audiology The study of hearing, especially hearing defects and their treatment. [AHD]
Audio magazine (1947-2000) America's first and longest running
audio magazine. Its demise after 53 years of continuous publication leaves
a huge void in the consumer audio world. Gone is the last great rational
voice, lost amidst the pseudoscientific din dominating high-end audio.
An audio warrior is dead and we are lessened. [Searchable back issues here.]
Audio
Timeline A most fascinating audio development timeline created
by three esteemed AES members, Jerry Bruck, Al Grundy
and Irv Joel, as part of the 50th anniversary of the AES.
audio websites A truly
astonishing and remarkable list of audio related websites compiled daily by Steve Ekblad. Also see Audio
& Hi-Fi Page, an equally astonishing and remarkable list of audio
related websites compiled by Tomi Engdahl. And for a refreshingly rational
voice on hot audio topics check out Rod
Elliott's site, particularly his get-rich-quick scheme for exploiting
the gullible regarding burning-in
audio cables. [Absolutely brilliant.]
auditionHearing. 1. The sense or power of hearing. 2. The act of hearing. [AHD]
auditory filter Term used to describe
the concept of critical bands. Analogous
to a bandpass filter with a rounded top ("rounded-exponential" after Patterson
and Moore, 1986). The filter is slightly asymmetric, being wider on the
low-frequency side.
auditory streaming(Shortened form of "auditory stream segregation" dubbed by Ulric Neisser.) Hearing. Term coined by Albert Bregman in his book Auditory Scene Analysisto describe the hearing phenomenon where we separate a continuous sound stream into discrete words or sounds. This explains, for example, the "cocktail party effect" where we separate out specific sounds (words) important to us from a cacophony of surrounding sound. Another example is that speech is a continuous audio stream, even though we "hear" separate words, yet there are no pauses in the audio stream. Yet another example is where musicians separate and listen to one or two instruments from among many playing at once. [I am vastly oversimplifying here to just give you a top-layer understanding. Hit the link and then obtain Bregman's book for the full treatment.]
aulosMusical Instrument. Ancient Egyptian double flute [See vase photo here.] Also used for single flute; hit the link for all the variations.
aural Of, relating to, or perceived by the ear. [AHD]
aural architecture The phrase coined by Blesser & Salter in their book: Spaces Speak, Are You Listening, to describe the complex phenomenon of how humans sense space by listening. Sensing spatial attributes is a nature human ability and the authors conclusively make the point that every environment has an aural architecture.
Aureal 3D (A3D) Proprietary 3D
sound technology first developed by Crystal River Engineering, which
became the advanced technology subsidiary of Aureal Semiconductor, alas,
now defunct. Aureal 3D made many claims. At one time their website
stated that "since we can hear sounds three dimensionally in the real world
by using two ears, it must be possible to create sounds from two speakers
that have the same effect" ... well ... NO ... it's pretty rhetoric,
but flawed logic. Our two ears receive sound coming from sources located
in every possible direction, and from that information process three-dimensional
location — that is not the problem. The problem is how to make our two
ears receive sound from sources located in only two directions, and trick
them into hearing three dimensionally -- that is the problem. Aureal claimed
to have solved this problem, but didn't stay in business long enough for
anyone to find out.
authoring DVD, CD or CD-ROM. A term used to indicate
more than writing, now used to include all the processes necessary (designing,
creating & editing) to add information of any sort onto a DVD, CD or
CD-ROM primarily providing search and retrieval features.
autoformerAutoformer is short for autotransformer,
or self-transformer, from the definition of auto-. An autotransformer
is one that self-magnetizes to produce the transformer voltage, it does
this by not having a true secondary, i.e., there is only one winding with
one part acting as the primary and the other part acting as the secondary,
but there is no second winding, and no air gap, and thus no true isolation
between the primary and secondary. Therefore an autotransformer is a transformer
in which part of one winding is common to both the primary and the secondary
circuits associated with that winding.
automatic attack & release Audio Compressors. Automatic attack and release designs typically look at the rate of change of the difference between the threshold and the current signal level (the error
signal). If the difference changes quickly, attack and release respond faster to the change. If the rate of change is small, attack and decay are slowed. The result is a relatively fast response to quick changes and a much slower response to slower changes, significantly reducing pumping and distortion. Digital designs do this using DSP algorithms. See THAT Corporation Design Note 114, Adaptive attack and release rates ... http://www.thatcorp.com/datashts/dn114.pdf for a description of an automatic scheme for an analog design.
automatic mic mixer A specialized
mixer optimized for solving the problems of multiple live microphones operating
together as a system, such as found in boardrooms, classrooms, courtrooms,
church systems, etc. An automatic mic mixer controls the live microphones
by turning up (on) mics when someone is talking, and turning down
(off) mics that are not used, thus it is a voice-activated, real-time
process, without an operator, hence, automatic. An automatic mic
mixer must adapt to changing background noise conditions. Further it must
control the additive effect of multiple mics being on at the same time
(see NOM). If one mic is on at maximum gain,
opening up another one may cause acoustic
feedback, so an automatic mixer must also control the system gain to
prevent feedback or excessive noise pickup. Dan
Dugan patented the first automatic mic mixer and is recognized as the
father of this technology. A final problem that automatic mixers solve
is maintaining a natural ambience from the room. This is especially critical
in recording and broadcasting. A good automatic mixer must make rapid and
dramatic changes in the gains of the input channels while maintaining the
sonic illusion that nothing is happening at all.
aux Nickname for auxiliary jack, found on audio equipment and used as an additional input or output.
aux fed subs, or aux fed subwoofers A live sound technique
becoming popular when subwoofers are used with the FOH system. It is claimed that a properly configured and operated aux fed subwoofer
system better maintains gain structure and crossover relationships. See
Tom Young's article at ProSoundweb, "A
Detailed Explanation Of The Aux Fed Subwoofer Technique."
AVB (Audio/Video Bridging) Networks. Name for the IEEE 802 emerging standard for gigabit Ethernet networks that is finding favor in the live sound industry to transport digital audio between the stage and the FOH console. Since this is a non-proprietary, i.e., no licensing fees, networking standard and is backed by giants Cisco and Intel, many pro audio companies are watching it closely. Also see: AoE.
AV Abbreviation for audio- video, referring to systems that contain both.
AVD (advanced video disk) A Chinese
proposed alternative to the DVD standard to
avoid paying what they consider exorbitant royalties. This threatened standard
would apply to DVD-like players sold only in China. Replaced by EVD.
AVnu Alliance (pronounced "avenue") From website: "An industry forum dedicated to the advancement of professional-quality audio video by promoting the adoption of the IEEE 802.1 Audio Video Bridging (AVB), and the related IEEE 1722 and IEEE 1733, standards over various networking link-layers."
AWG (American wire gauge) A specification
for non-ferrous (e.g., copper, aluminum, gold, silver, etc.) wire diameter.
[Note, for example, that this means that 14 gauge galvanized steel wire
& 14 gauge cooper wire have different diameters.] Also known as Brown and Sharp (B&S) wire gauge, after J.R. Brown who devised
the system in 1857 (I have been unsuccessful in finding out what Sharpe's
role was). For more detail, see Douglas
Brooks' "How to Gauge Traces." Many tables exist on the Internet. The British
standard is called SWG standing for Standard wire gauge,
also called Imperial wire gauge.
AZA (Association of Zoos and Aquariums) "AZA-accredited zoos and aquariums are leaders in the protection of endangered species." Another resource for audio contractors, integrators, etc.
azimuth 1. The horizontal angular distance
from a reference direction, usually the northern point of the horizon,
to the point where a vertical circle through a celestial body intersects
the horizon, usually measured clockwise. Sometimes the southern point is
used as the reference direction, and the measurement is made clockwise
through 360° 2. The horizontal angle of the observer's bearing in surveying,
measured clockwise from a referent direction, as from the north, or from
a referent celestial body, usually Polaris. 3. The lateral deviation of
a projectile or bomb. [AHD]
azimuth recording Recording. Magnetic recording trick that reduces crosstalk between adjacent tracks.
