| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to efficiently code sound signals even at a low bit rate by sub-band-coding sound signals and extracting features by short-time frames from the obtained narrow band signals. SOLUTION: Inputted PCM audio signals are supplied also to a sub-band filter 11 in parallel with a FET circuit 13. In the sub-band filter 11, the signals are equally divided into, for example, 32 sub-bands and, in addition, supplied to a frame processing circuit 12 for every sub-band to be divided into frame of every specified period of time and outputted to an envelope extracting circuit 19. This circuit 19 extracts envelopes of amplitude calculated for every short- time frame. And, using a zero-cross counting circuit 12, the number of zero crossings of amplitude is calculated for every short-time frame. Thus, the envelopes quantized for every sub-band and the number of zero-crossings are supplied to a multiplexer 16 to be multiplexed and outputted to the transmission line as bit stream. |
