| 摘要 |
<p>A digital signal processing apparatus for encoding an input digital signal. The apparatus comprises a predictive filter (3) supplied with the input digital signal for generating a filtered output, a circuit for controlling the frequency characteristics of the predictive filter, a predictive error detector for detecting a difference signal between the input digital signal and the filtered output (8), a frequency spectrum detector (32) for detecting the frequency spectrum of the input digital signal during every predetermined period, a re-quantizer (12) for re-quantizing the difference signal, a re-quantizing error detector (21) for detecting a re-quantizing error signal (SZ2), a noise filter (9) supplied with the re-quantizing error signal and producing an output signal fed back to the output of the re-quantizer, and a noise filter controller (33) for controlling the frequency characteristics of the noise filter in response to the output of the frequency spectrum detector. In this apparatus, the amount of calculations required for detecting the spectrum and selectively determining the frequency characteristics of the noise filter is reduced to consequently achieve efficient re-quantization of the input digital signal, hence improving the signal-to-quantization noise ratio with a simplified structure.</p> |
