Survey of voiceband data signal compression

Today's public switched telephone networks are being upgraded to use digital transmission and switching. The main disadvantage of digital transmission is the higher bandwidth required. To alleviate this problem, much research has been devoted into the compression of digitized voice signals. However, such compression techniques tend to have adverse effects on non-voice signals such as modems and faxes. Only recently has the area of voiceband data signal compression been explored. This paper covers some of the highlights of these publications including DPCM, delta modulation, low delay code excited linear prediction, and vector quantisation.