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Journal of the Audio Engineering Society

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2004 June - Volume 52 Number 6

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Papers

Efficient Generation of Multichannel Dither Signals

Authors: Wannamaker, Robert A.

Means for generating dither signals and the use of dither in multichannel quantizing systems are explored. After general recommendations are offered regarding the generation of suitable pseudorandom sequences for dithering purposes, efficient approaches to generating dither for use with multiple data channels are addressed. Practical properties required of multichannel dither signals are discussed, including the requirements that they render desired statistical properties of the total error signal in each channel independent of the input to that channel, and that errors in different channels be uncorrelated with one another. Methods of designing computationally efficient multichannel dither generation schemes meeting these criteria are presented with examples.

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Time-Quantized Frequency Modulation, Time-Domain Dither, Dispersive Codes, and Parametrically Controlled Noise Shaping in SDM

Authors: Hawksford, Malcolm J.

Time-domain quantization (TDQ) and noise shaping applied to linear frequency modulation (LFM) offers an alternative although unconventional means of generating uniformly sampled 1-bit code with characteristics similar to that generated by feedback sigma-delta modulation (SDM). Fundamental insight into the SDM process emerges by exploiting the relationship between uniform quantization and phase modulation. Linearity and output noise spectra are benchmarked against linear pulse-code modulation (LPCM) and error spectra derived by comparing 1-bit SDM against an identical feedback loop but without quantization. Sony FF class SDM is discussed and an example is shown to achieve almost noiseless performance from 0 Hz to 30 kHz by incorporating parametrically determined noise shaping stabilized by step-back in time closed-loop control.

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Augmented Reality Audio for Mobile and Wearable Appliances

Authors: Härmä, Aki; Jakka, Julia; Tikander, Miikka; Karjalainen, Matti; Lokki, Tapio; Hiipakka, Jarmo; Lorho, Gaëtan

The concept of augmented reality audio characterizes techniques where a real sound environment is extended with virtual auditory environments and communications scenarios. A framework is introduced for mobile augmented reality audio (MARA) based on a specific headset configuration where binaural microphone elements are integrated into stereo earphones. When microphone signals are routed directly to the earphones, a user is exposed to a pseudoacoustic representation of the real environment. Virtual sound events are then mixed with microphone signals to produce a hybrid, an augmented reality audio representation, for the user. An overview of related technology, literature, and application scenarios is provided. Listening test results with a prototype system show that the proposed system has interesting properties. For example, in some cases listeners found it very difficult to determine which sound sources in an augmented reality audio representation are real and which are virtual.

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Room Sizing and Optimization at Low Frequencies

Authors: Cox, Trevor J.; D'Antonio, Peter; Avis, Mark R.

Modes in small rooms may lead to uneven frequency responses and extended sound decays at low frequencies. In critical listening environments, this often causes unwanted coloration effects, which can be detrimental to the sound quality. Choosing an appropriately proportioned room, and placing listener and loudspeakers in the right places can reduce the audible effects of modes. A new methodology is detailed for determining the room dimensions for small critical listening spaces as well as the optimum positions for sources and receivers. It is based on numerical optimization of the room geometry and layout to achieve the flattest possible frequency response. The method is contrasted with previous techniques for choosing room dimensions. The variations of the room quality for different room sizes are mapped out. These maps include an allowance for constructional variation, which has not been considered previously.

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How Loud Is My Broadcast?

Authors: Staff, AES

[feature] The topic of program loudness arouses strong passions in listeners and broadcasters alike. It is the subject of numerous complaints to television and radio organizations from listeners who get irritated when they are either deafened by an unreasonable rise in perceived level, or when they suddenly can’t hear the movie dialogue because they have turned the volume down during loud commercials. The problem, according to researchers, seems to be getting worse rather than better in the age of digital broadcasting, where conventions regarding peak levels seem to be treated somewhat casually and where recommendations concerning normal dialogue levels seem to be flaunted or ignored.

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