An advanced 32 kbit/s ADPCM coding to transmit speech and high-speed voiceband data

This paper describes a performance evaluation of an advanced 32 kbit/s ADPCM hardware codec in terms of speech and high-speed voiceband data, V.27 and V.29 at 4.8, 7.2 and 9.6 kbit/s. The results indicated that the advanced 32 kbit/s ADPCM provided an equivalent subjective speech quality to that of the G.721 ADPCM recommended by the CCITT, and was able to maintain the transparency of these high-speed voiceband data at 7.2 kbit/s over at least four and at 9.6 kbit/s over at least two asynchronous tandem links, respectively. Furthermore, the advanced ADPCM can quickly recover a complete synchronous operation in the tandem connections, as burst errors or short-hits damage the digital links.