Adaptive Delta Modulation (ADM) coding is economical method of digitally encoding speech signals. It is a one-bit differential coding scheme which compares the source signal x(t) to an approximate signal xˆ(t) which is then increased or increased by a predetermined step size. This step size is adapted in proportion to the recent average slew rate of the input signal. For a given average signal slope, there is an optimum step size which will result in the maximum signal-to-quantisation noise ratio (SNR) q , and it is desirable to adapt accordingly. In this paper, design and implementation of the continuously variable slope adaptive delta modulation (CVSD) are considered. To study the effects of channel errors and data encryption (scrambling) on the performance of the system, a channel simulator, noise generator, and encrypter/decrypter are also design and constructed. Experiments showed that the system provides high quality speech reproduction at bit rates of 32 kbps and ISdẞ SNR on transmission channel. transmission channel. Moreover, a good quality speech reproduction is obtained at 16 kbps and 20dẞ SNR on transmission channel. The system reported here may be suitable for secure military communication, in a half-duplex mode, over noise corrupted channels.
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