Process for varying speech speed and device for implementing said process

• US 5,073,938 A
• Filed: 10/17/1989
• Issued: 12/17/1991
• Est. Priority Date: 04/22/1987
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Galand, Claude
• Primary Examiner(s): Harkcom, Gary V.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US07/423,732
• Time in Patent Office: 791 Days
• Field of Search: 381/29-41, 381/51-53, 364/513.5, 375/122
• US Class Current: 704/207
• CPC Class Codes: G10L 21/04 Time compression or expansion

Abstract

The process for varying the speed of a speech signal that involves splitting at least a portion of the speech frequency bandwidth into N narrow sub-bands, processing each sub-hand signal contents to derive therefrom magnitude data M(i, n) and phase data P(i, n), i=1, . . . , N being the subband index and n the time index. The M (i, n) sequence is converted into a sequence M'"'"'(n) by either duplicating one sample every K samples (K being an integer value derived from the desired slowing-down/speeding up ratio). The phase sequence P (i, n) is processed to derive therefrom an increment sequence D(i, n)=P(i, n)-P(i, n-1), which increment sequence is first converted into a D'"'"'(i, n) sequence by either dropping or duplicating one sample every K, samples, before being converted into P'"'"'(i, n)=P'"'"'(i, n)+D'"'"'(i, n). The P'"'"'(i, n), D'"'"'(i, n) sequences are converted back into sub-band signals contents, then combined together into the slowed-down/speeded-up speech signal.

Claims

1. An apparatus for digitally varying the speed of a speech signal having a speech frequency bandwidth without measuring or substantially varying the pitch of the speech signal, including:

means for splitting at least a portion of the speech frequency bandwidth of said speech signal into a plurality of consecutive narrow sub-band signals;

means for processing each of said sub-band signals to derive therefrom phase samples and magnitude samples representative of the sub-band signal contents expressed in polar coordinates;

means for speed varying said sub-band signals by repeating phase and magnitude samples or deleting samples therefrom at a rate depending upon the desired slowing-down or speeding-up rate respectively;

means for recombining each sub-band phase and magnitude samples into a speed varied sub-band signal; and

means for recombining said speed varied sub-band signals into recombined speech, whereby said recombined speech is a speed varied version of said speech signal having substantially the same pitch as said speech signal.

2. An apparatus for speed varying a speech signal sampled at frequency fs without measuring or substantially varying the pitch of the speech signal, characterized in that it includes:

a first bank of quadrature mirror filters (QMF) for splitting a limited bandwidth of said speech signal into a plurality of N narrow sub-band signals, N being an integer value greater than 1;

first down sampling means, connected to said QMF bank for down sampling each of said sub-band signals at a rate fs/N;

complex quadrature mirror filtering (CQMF) means connected to said first down sampling means for converting each down sampled sub-band signal into an analytical signal represented by in-phase and quadrature components;

second down sampling means connected to said CQMF for down sampling said in-phase and quadrature components to fs/2N;

coordinate converting means connected to said second down sampling means for converting said analytical signal into magnitude component M(i,n) samples and phase component P(i,n) samples, with i=1. . ., N being the sub-band index and n being the time index;

speed variation means connected to said coordinate converting means for deleting or repeating samples of said magnitude component M(i,n) and said phase component P(i,n) at a rate depending upon the desired speech rate variation whereby M'"'"'(i,n) data are generated from said magnitude component M(i,n) and P'"'"'(i,n) data are generated from said phase component P(i,n);

coordinate converting means connected to said speed variation means for converting said M'"'"'(i,n) and P'"'"'(i,n) into rate converted analytical data u'"'"'(i,n) and v'"'"'(i,n) respectively;

inverse complex QMF filtering means (ICQMF) connected to the output of said coordinate converting means for up sampling said rate converted analytical data u'"'"'(i,n) and v'"'"'(i,n) to a rate fs; and

,

an inverse QMF filter bank connected to the output of said ICQMF means for providing a speed varied speech signal s'"'"'(n), said speed varied speech signal s'"'"'(n) having a pitch substantially the same as said speech signal.

3. A method for digitally varying the speed of a speech signal without measuring or substantially varying the pitch of the speech signal, said method comprising the steps of:

splitting at least a portion of the speech frequency bandwidth of said speech signal into a plurality of consecutive narrow sub-band signals;

processing each of said sub-band signals to derive therefrom phase samples and magnitude samples representative of the subband signal contents expressed in polar coordinates;

speed varying said sub-band signals by repeating phase and magnitude samples or deleting samples therefrom at a rate depending upon the desired slowing-down or speeding-up rate respectively;

recombining each of said speed varied sub-band phase and magnitude samples into a speed varied sub-band signal; and

recombining said recombined speed varied sub-band signals into recombined speech, whereby said recombined speech is a speed varied version of said speech signal having substantially the same pitch as said speech signal.

4. The method according to claim 3 wherein said sub-band processing to derive phase and magnitude samples includes:

deriving from each of said sub-band signals an analytical signal consisting of an in-phase component and a quadrature component through use of complex quadrature mirror filtering techniques;

sampling-down said analytical signal by dropping every other sample from said in-phase and quadrature components; and

, converting said sampled down analytical signal into phase and magnitude samples.

5. A method according to claim 3 wherein said sub-band signal is sped-up at a rate K/K-1, with K being an integer having a value greater than 1, including dropping one out of K magnitude samples;

and dropping one out of K phase samples.

6. The method according to claim 3 wherein said sub-band signal is slowed down at a rate K/K+1, with K being an integer having a value grater than 0, including computing a phase sample and repeating said computed phase sample and one magnitude sample every K samples.

7. The method according to claim 3 wherein said portion of the speech frequency and width is limited to the speech signal base-band.

8. An apparatus for speed varying a speech signal sampled at frequency fs, characterized in that it includes:

a first bank of quadrature mirror filters (QMF) for splitting a limited bandwidth of said speech signal into a plurality of N narrow sub-band signals, N being an integer value greater than 1;

first down sampling means, connected to said QMF bank for down sampling each of said sub-band signals at a rate fs/N;

complex quadrature mirror filtering (CQMF) means connected to said first down sampling means for converting each down sampled sub-band signal into an analytical signal represented by in-phase and quadrature components;

second down sampling means connected to said CQMF for down sampling said in-phase and quadrature components to fs/2N;

coordinate converting means connected to said second down sampling means for converting said analytical signal into magnitude component M(i,n) samples and phase component P(i,n) samples, with i=1, . . ., N being the sub-band index and n being the time index;

speed variation means connected to said coordinate converting means for deleting or repeating samples of said magnitude component M(i,n) and said phase component P(i,n) at a rate depending upon the desired speech rate variation whereby M'"'"'(i,n) data are generated from said magnitude component M(i,n) and P'"'"'(i,n) data are generated from said phase component P(i,n);

said speed variation means further including;

means for generating a sequence of magnitude signal components M(n) for each sub-band of said magnitude component M(i,n);

means for generating a sequence of phase signal components P(n) for each sub-band of said phase component P(i,n);

means for speeding up said speech signal at a rate K/K-1 K being a predetermined integer having a value greater than 1, including, for each sub-band;

means for converting the sequence of magnitude signal components M(n) into a speeded-up M'"'"'(n) by deleting every Kth M(n) sample;

means for generating a phase increment component sequence D(n) according to

space="preserve" listing-type="equation">D(n)=P(n)-P(n-1)

means for converting the D(n) component sequence into D'"'"'(n) by deleting every Kth sample from D(n); and

,

means for generating a speeded-up phase sequence

space="preserve" listing-type="equation">P'"'"'(n) with;

space="preserve" listing-type="equation">P'"'"'(n)=P'"'"'(n-1)+D'"'"'(n)

means for slowing down the speech signal at a rate K/K+1 K being a predetermined integer having a value greater than 0, including for each sub-band;

means for converting the sequence of magnitude signal components M(n) into a slowed-down sequence M'"'"'(n) by repeating every Kth M(n) sample;

means for generating a phase increment component sequence D(n) according to

space="preserve" listing-type="equation">D(n)=P(n)-P(n-1)

means for converting the D(n) component sequence into D'"'"'(n) by duplicating every Kth sample and;

means for generating a slowed-down phase sequence

space="preserve" listing-type="equation">P'"'"'(n) with;

space="preserve" listing-type="equation">P'"'"'(n)=P'"'"'(n-1)+D'"'"'(n)

coordinate converting means connected to said speed variation means for converting said M'"'"'(i,n) and P'"'"'(i,n) into rate converted analytical data u'"'"'(i,n) and v'"'"'(i,n) respectively;

inverse complex QMF filtering means (ICQMF) connected to the output of said coordinate converting means for up sampling said rate converted analytical data u'"'"'(i,n) and v'"'"'(i,n) to a rate fs; and

,

an inverse QMF filter bank connected to the output of said ICQMF means for providing a speed varied speech signal s'"'"'(n).