High-performance ADPCM codec for voice and voiceband data and its application to DCME

An advanced adaptive differential pulse-code modulation (ADPCM) technique applicable to digital circuit multiplication equipment (DCME) is described. The performance of the advanced ADPCM CMOS single-chip codec regarding voice and various high-speed modems is discussed. Major issues in DCME are also addressed. The speech quality of the 32 kb/s advanced ADPCM is equivalent to that of CCITT G.721 ADPCM and also provides better quality at 24 kb/s. The 32 kb/s advanced ADPCM can transmit V.29 modem signals at 9600 b/s over two asynchronous tandem links and V.32 modem signals over four asynchronous tandem links, respectively. Evaluation results indicate that at 40 kb/s, the advanced ADPCM again provides superior performance to the 40 kb/s G. 721-based ADPCM for V.33 modem at 14.4 kb/s. It is noted that an advanced ADPCM codec having a variable rate coding capability between 24 and 32 kb/s effectively can be applied to DCME allowing a higher gain and better speech quality to be achieved.<>