Purpose: The spatiotemporal index (STI) is one measure of variability. As currently implemented, kinematic data are used, requiring equipment that cannot be used with some patient groups or in scanners. An experiment is reported that addressed whether STI can be extended to an audio measure of sound pressure of the speech envelope over time that did not need specialized equipment. Method: STI indices of variability were obtained from lip track (L-STI) and amplitude envelope (E-STI) signals. These measures were made concurrent while either fluent speakers or speakers who stutter repeated "Buy Bobby a puppy" 20 times. Results: L-STI and E-STI correlated significantly. STI decreased with age for both L-STI and E-STI. E-STI scores and L-STI scores discriminated successfully between fluent speakers and speakers who stutter. Conclusion: The amplitude-envelope-over-time signal can be used to obtain an STI score. This STI score can be used in situations where lip movement STI scores are precluded. (Contains 5 figures, 1 table and 1 footnote.)