ADPCM transcoder wherein different bit numbers are used in code conversion

摘要

For transmission and reception of an ADPCM stream in which each of signal components is represented by a predetermined number of bits, an ADPCM transcoder comprises a bit number determining device (43) for producing a bit number signal representative of first and second bit numbers one at a time to make the ADPCM stream carry a voice component with the first bit number and a data component with the second bit number as two of the signal components. The first bit number is less than the second bit number. Preferably, a sum of the first and the second bit numbers is not greater than twice the predetermined number to make one of the two signal components comprise the voice component and a less significant part of the data component. The first and the second bit numbers are calculated from a voice and a data optimum scale factor which can be calculated by a method similar to adaptive prediction. The bit number signal need not be carried by the ADPCM stream. Alternatively, the transcoder may multiplex the bit number signal in the ADPCM stream for transmission and demultiplex the bit number signal from the ADPCM stream received to determine the first and the second bit numbers for use in an ADPCM decoder included therein.