Abstract
Abstract : Intelligibility tests were conducted for speech presented over eight bandwidth compression systems. At a SNR of +26 dBA there is little difference in intelligibility scores for the Linear Predictive Coding (LPC) and Channel Vocoder, both systems scoring higher than the Continuously Variable Slope Delta Modulation (CVSD) system but lower than the Analog Reference system. The best performance among the digitized compression systems is achieved by the Culler- Harrison and Lincoln Lab LPC systems operating at 3500 bits/second, but the Channel Vocoder operating at 2400 bits/seconds was less adversely affected by noise at the speech input. Except for the CVSD systems, adding more noise significantly degrades performance. The LPC systems are particularly vulnerable, suggesting that these systems have been designed to maximize operation in a noise-free environment. Further research should be oriented toward improving performance in typical noise environments.
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