e to their different companding schemes, by act- ing as a common language between the two PCM schemes. There is also a recommendation for an ADPCM algorithm (G.722) that will code 7.1-kHz bandwidth audio signals into 64 Kbps. This coding scheme improves the quality of speech and it can be used for good quality voice over ISDN networks. ADPCM systems are available on the market that convert two primary rate PCM streams into one data stream at the same rate by using ADPCM. Two 32-Kbps ADPCM channels occupy one ordinary PCM channel. Net- work operators use ADPCM to utilize long-distance transmission systems, for example, submarine systems, more efficiently. Another application exam- ple is in PABX networks where the offices of private enterprises are intercon- nected by leased-line 64-Kbps channels. ADPCM doubles the capacity of these expensive leased lines between PBX/PABXs. One application for ADPCM is also in cordless telephones such as digital enhanced cordless tele- communications (DECT). The ADPCM coding scheme is based on the statistics of speech and it does not support modem or facsimile signals at higher data rates than 4,800 bps. Because of this, telecommunications network operators cannot use ADPCM instead of PCM coding for all calls. This is a problem if ADPCM systems are used inside a telecommunications network. One way to over- come this problem is to have the ADPCM encoder detect whether a data or facsimile connection is to be established and in that case disable the PCM/ADPCM transcoder for that channel. Up to this point we have discussed primarily waveform coding meth- ods. The phrase waveform coding refers to attempts to describe the shape or the waveform of the original analog signal, just as PCM, DPCM, and ADPCM do. In a more efficient coding scheme in terms of data rate, such as voice coding, which is implemented by vocoders, we divide speech into seg- ments with lengths of some tens of milliseconds. Then we analyze each seg- ment to find a model that describes it best and send parameters of the