An Analysis off 16 kb/s Sub-Band Coder Performance: Dynamic Range, Tandem Connections, and Channel Errors

In this paper, we examine the performance of sub-band encoding under a number of constraints which can exist in practical digital communications systems. In particular, we investigate the effects of varying input signal levels, tandem connections, and channel errors on the performance of sub-band coders. A coder bit rate of 16 kb/s is used in all the simulations. The dynamic range performance is evaluated for a 50-dB range of input signal levels. Tandem connections of up to four sub-band coders in tandem are examined. Finally, the effects of random channel errors on the performance of sub-band coders is examined for bit error probabilities of up to 10 percent. A robust coder design with partial bit error protection is also proposed for use in very high channel error environments.

Three different performance measures were used in these simulations, the conventional signal-to-noise ratio, a segmental signal-to-noise ratio, and an lpc distance measure. By comparing the results of these various performance measures and from informal assessments of subjective quality, we gain some new insights into the advantages and disadvantages of these measures in terms of their usefulness in predicting coder quality.