| 摘要 |
<p>A variable rate coder for transforming an input signal into a low bit rate digital signal, comprising: a plurality of coding units (111, 121, 131) each comprising an output quantizer having a different number of output bits, and each independently transforming the input signal into a compressed digital signal. A plurality of bit rate determining circuits (24, 3a) are provided to determine an output of one of the plurality of coding units (111, 121, 131) as an output of the coder by an individual determining method, in which method, quality of a signal which is regenerated from an output of each coding unit is compared with an individual predetermined quality evaluating standard, and then an output of a coding unit having a smallest number of output bits among outputs of coding units satisfying each standard, is determined as the output of the coder. One output among the plurality of the above determined outputs, which is determined by a most suitable determining method for the level of the input signal, is used to select the output of the coder (Fig. 1). Further, when the number of the output in each of the coding untis (111, 121, 131) can be variably set, the most suitable number of output bits for the output of the coder is calculated based on prediction gains of the coding units (111, 121, 131), a required signal-to-noise ratio of the coder, and an ADC signal-to-noise ratio at the analog to digital converter, and the number of the output in each of the coding units (111, 121, 131) is set based on the above calculated value, before the above operation by the bit rate determining circuits (24, 3a).</p> |
