Digital signal sub-band separating/combining apparatus achieving band-separation and band-combining filtering processing with reduced amount of group delay

Abstract

An apparatus having a band-separating filter bank for separating a digital signal into a plurality of sub-band signals, to be processed or transmitted, and a band-combining filter bank for subsequently combining the resultant sub-band signals into a single digital signal, wherein each of the band-separating filter bank and band-combining filter bank incorporates a FIR low pass filter having an asymmetric impulse response, as the prototype filter of the filter bank. A significant reduction can thereby be achieved in the amount of overall group delay that results from the processing performed by these filter banks.

1 . A digital signal low-delay sub-band separating apparatus formed of a plurality of filters corresponding to respective frequency bands, for separating an input digital signal into a corresponding plurality of sub-band signals, and decimation means for applying digital signal sample decimation to each of said sub-band signals; 
 wherein said apparatus comprises, as a prototype filter of said plurality of filters, a FIR (finite impulse response) low-pass filter which is configured to have a response characteristic that is asymmetric with respect to the origin.    
   
   
       2 . A digital signal low-delay sub-band combining apparatus formed of a plurality of filters corresponding to respective frequency bands, for filtering corresponding ones of a plurality of sub-band signals supplied thereto, interpolation means for applying digital signal sample interpolation to each of said sub-band signals subsequent to said filtering, and means for additively combining respective output sub-band signals from said interpolation means to form a single digital signal; 
 wherein said apparatus comprises, as a prototype filter of said plurality of filters, a FIR (finite impulse response) low-pass filter which is configured to have a response characteristic that is asymmetric with respect to the origin.    
   
   
       3 . A digital signal encoder apparatus comprising sub-band separating means for converting an input digital signal to a plurality of sub-band signals and encoding means for respectively encoding said sub-band signals and combining resultant encoded data into a data stream to be transmitted or processed; 
 wherein said sub-band separating means comprises a sub-band separating apparatus as claimed in  claim 1 .    
   
   
       4 . A digital signal decoder apparatus for operating on an input data stream formed of combined encoded data of a plurality of sub-band signals, comprising decoding means for recovering said plurality of sub-band signals from said data stream and sub-band combining means for combining said recovered sub-band signals into a single output digital signal; 
 wherein said sub-band combining means comprises a sub-band combining apparatus as claimed in  claim 2 .    
   
   
       5 . A digital signal encoder apparatus according to  claim 3 , wherein said encoding means performs encoding processing by applying a high-speed algorithm which utilizes the periodicity of a cosine function.  
   
   
       6 . A digital signal decoder apparatus according to  claim 4 , wherein said decoding means performs decoding processing by applying a high-speed algorithm which utilizes the periodicity of a cosine function.  
   
   
       7 . A digital signal encoder apparatus according to  claim 3  wherein said input digital signal is a PCM (pulse code modulation) digital audio signal and wherein said encoding comprises compression encoding of said PCM digital audio signal.  
   
   
       8 . A digital signal low-delay decoder apparatus according to  claim 4 , wherein said plurality of sub-band signals express a single PCM (pulse code modulation) digital audio signal and have been encoded by compression encoding processing, and wherein said decoding processing performed by said decoder apparatus comprises expansion decoding to recover said plurality of sub-band signals from said data stream and combining said sub-band signals into a single digital PCM audio signal.  
   
   
       9 . A transmitter apparatus for a digital wireless microphone system, having analog-to-digital converter means for converting an analog audio signal from a microphone to a digital audio signal and encoder means for converting said digital audio signal to an encoded compressed data stream, wherein said encoder means comprises a digital signal encoding apparatus as claimed in  claim 3 .  
   
   
       10 . A receiver apparatus for a digital wireless microphone system, for receiving a data stream formed by compression encoding of a plurality of sub-band signals derived from an original digital audio signal, having decoder means for recovering said original digital audio signal from said data stream, wherein said decoder means comprises a digital signal decoder apparatus as claimed in  claim 4 .  
   
   
       11 . (canceled)  
   
   
       12 . A digital signal low-delay sub-band separating apparatus formed of a plurality of filters corresponding to respective frequency bands, for separating an input digital signal into a corresponding plurality of sub-band signals, and decimation means for applying digital signal sample decimation to each of said sub-band signals; 
 wherein said apparatus comprises, as a base filter of said plurality of filters, a FIR (finite impulse response) low-pass filter having an impulse response formed by N filter taps, and having an impulse response coefficient h[k] that satisfies a condition:        h[k]≠±h[N− 1 −k],      where 0≦k≦S k int(N/2)−1, with int(N/2) being the integer part of (N/2).    
   
   
       13 . A digital signal low-delay sub-band combining apparatus formed of a plurality of filters corresponding to respective frequency bands, for filtering corresponding ones of a plurality of sub-band signals supplied thereto, interpolation means for applying digital signal sample interpolation to each of said sub-band signals subsequent to said filtering, and means for additively combining respective output sub-band signals from said interpolation means to form a single digital signal; 
 wherein said apparatus comprises, as a base filter of said plurality of filters, a FIR (finite impulse response) low-pass filter having an impulse response formed by N filter taps, and having an impulse response coefficient h[k] that satisfies a condition:        h[k]≠+h[N− 1 −k],      where 0≦k≦int(N/2)−1, with int(n/2) being the integer part of (N/2).