US 4,799,179 AGranted

Signal analysing and synthesizing filter bank system

AssigneeTelecommunications Radioelectriques et Telephoniques T.R.T.

InventorsJacques L. R. Masson, Zdenek Picel

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Abstract

In a signal analysing and synthesizing filter bank system, the analysing bank receives a signal sampled at the rate f.sub.e and produces N contiguous subbank signals sampled at the rate f.sub.e /N. From the subband signals the synthesizing bank must recover the incoming signal. These filter banks are formed by modulation of a prototype filter by sinusoidal signals which, for subband k (O.ltoreq.k.ltoreq.N=1), have a frequency (2k30 1)f.sub.e /(4N) and respective phases +(2k+1).pi./4 and -(2k+1).pi./4 for the analysing and synthesizing banks. These signals are furthermore delayed by a time delay (N.sub.c -1)/2f.sub.e), where N.sub.c is the number of coefficients of the prototype filter. Preferably, the analysing bank is realized by the cascade arrangement of an N-branch polyphase network (12) and a double-odd discrete cosine transform calculating arrangement (14) and the synthesizing bank is realized by the cascade arrangement of a double-odd discrete cosine transform calculating arrangement (15) and an N-branch polyphase network (17).

Claims5

Dependent claims

A digital signal processing system comprising:

a. an analysing filter bank for dividing an incoming signal, sampled at a rate f.sub.3 and occupying a frequency band limited to f.sub.e /2, into N contiguous subband signals having respective bandwidths of f.sub.e /2N and which are sampled at a rate f.sub.e /N, said analyzing filter bank comprising N prototype low-pass filters, one for each subband and arranged in parallel along N respective branches, each prototype filter:
i. having a same finite and symmetrical impulse response;
ii. having a beginning-of-attenuation-band frequency f.sub.a less than f.sub.e /2N;
and
iii. satisfying the condition H.sup.2 (f)+H.sup.2 (f.sub.e /2N-f)=1 in a band of frequencies f extending from 0 to f.sub.a, where H(f) is the absolute value of the frequency response to each prototype filter;
and
iv. comprising a modulation input for receiving a modulation signal, each modulation signal having:
A. a frequency f.sub.k =(2k+1)f.sub.e /(4N), where k is an integer, running from 0 N-1, representing a respective one of the N subbands;
B. a phase .alpha..sub.k, such that .alpha..sub.0 is equal to one of .pi./4, 3.pi./4, 5.pi./4, and 7.pi./4, and such that for two contiguous subbands represented by k and k-1, the difference .alpha..sub.k -.alpha..sub.k-1 is equal to one of .pi./2 and -.pi./2;
and
C. a time delay .tau.=(N.sub.c -1)/(2f.sub.e), where N.sub.c is a number of coefficients required for realizing the prototype filter;
and
b. a synthesizing filter bank for recoverying said incoming signal from said subband signals, said synthesizing filter bank comprising N prototype low-pass filters which are the same as the prototype filters used in the analyzing filter bank, except that the phase of the modulation signals is -.alpha..sub.k,
whereby the number N is any integer greater than or equal to 2 and whereby N.sub.c is not constrained to be a multiple of N.

11 more elements

A digital signal processing system comprising an analysing filter bank for dividing an incoming signal, sampled at a rate f.sub.e and occupying a frequency band limmited to f.sub.e /2, into N contiguous subband signals X.sub.k (m) having respective bandwidths of f.sub.e /2N and each being sampled at a rate of f.sub.e /N, the analyzing filter bank comprising a polyphase network which comprises:

a. means for distributing N samples of the incoming signal over N branches in each period NT, with T=1/f.sub.e ;
b. first means for calculating N signals P.sub..rho. (m) from .lambda. consecutive signals entering the .rho.th branch and from a set of coefficients, said first calculating means having N inputs for receiving the samples from the distributing means, where .rho. is an integer varying from 0 to N-1, .lambda. is the integer part of (N-N.sub.c +1)/N, and N.sub.c is the number of coefficients in the set;
c. N second means for calculating a double-odd discrete cosine transform, each second calculating means having N inputs for receiving the signals P.sub..rho. (m) and having an output at which a subband signal X.sub.k (m) is supplied, said subband signal being formed according to the following formulae:
i. for .lambda. odd and for .lambda. even and N even:
##EQU39## ii. for .lambda. even and N odd:
##EQU40## whereby the analyzing filter bank filters an incoming signal according to a frequency response which is given by a succession of N elementary frequency responses, each of the N frequency responses having a shape which corresponds to a frequency response to a same prototype filter, which prototype filter is defined by the N.sub.c coefficients and supplied with a modulation input for receiving a plurality of signals having respective frequencies and whereby N is any integer greater than or equal to two and whereby N.sub.c is not constrained to be a multiple of N.

3 more elements

Dependencies are inferred from the claim text.