RCELP coder

• US 5,704,003 A
• Filed: 09/19/1995
• Issued: 12/30/1997
• Est. Priority Date: 09/19/1995
• Status: Expired due to Term

• Current Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Nahumi, Dror, Kleijn, Willem Bastiaan
• Primary Examiner(s): MacDonald, Allen R.
• Assistant Examiner(s): MATTSON, ROBERT
• Application Number:
  US08/530,040
• Time in Patent Office: 833 Days
• Field of Search: 395/2.25-2.29
• US Class Current: 704/220
• CPC Class Codes: G10L 19/09 Long term prediction, i.e. removing periodical redundancies, e.g. by using adaptive codebook or pitch predictor

Abstract

An improved method of speech coding for use in conjunction with speech coding methods wherein speech is digitized into a plurality of temporally defined frames, each frame including a plurality of sub-frames, and the digitized speech is partitioned into periodic components and a residual signal. For each of a plurality of sub-frames of the residual signal, the improved method of speech coding selects and applies a time shift T to the sub-frame by applying a matching criterion to (a) the current sub-frame of the residual signal, and (b) a sample-to-sample (subframe-to-subframe) pitch delay determined by applying linear interpolation to known pitch delays occurring at or near frame-to-frame boundaries of previous frames.

The matching criterion is applied by minimizing ε, where: ##EQU1## (r(n-T)) is the residual signal of the current frame shifted by time T, r(n-D(n)) is the delayed residual signal from a previously-occurring frame, n is a positive integer, r is the instantaneous amplitude of the residual signal, and D(n) is the sample-to-sample pitch delay determined by applying linear interpolation to known pitch delay values occurring at or near frame-to-frame boundaries.

Claims

1. A method of speech coding for use in conjunction with speech coding methods wherein speech is digitized into a plurality of temporally defined frames, each frame having a plurality of sub-frames including a current sub-frame present during a specified time interval, each frame having a pitch delay value specifying the change in pitch with reference to the immediately preceding frame, each sub-frame including a plurality of samples, and the digitized speech is partitioned into periodic components and a residual signal;

the improved method of speech coding comprising the steps of;

(a) for each of a plurality of sub-frames of the residual signal, determining a time shift T based upon (i) the current sub-frame of the residual signal, and (ii) a delayed residual signal from a previously-occurring frame; and

(b) applying the time shift T determined in step (a) to the current sub-frame of the residual signal.

2. An improved method of speech coding as set forth in claim 1 wherein the time shift T is determined using a matching criterion defined as ##EQU8## wherein (r(n-T)) is the residual signal of the current frame shifted by time T, r(n-D(n)) is the delayed residual signal from a previously-occurring frame, n is a positive integer, r is the instantaneous amplitude of the residual signal, and D(n) represents the sample-to-sample pitch delay determined by applying linear interpolation to known pitch delay values occurring at or near frame-to-frame boundaries.

3. A method of speech coding as set forth in claim 2 wherein the time shift T is determined so as to minimize the matching criterion ε

, wherein ε

represents the correlation between a sub-frame of the residual signal and a time-shifted version of that residual signal.

4. A method of speech coding as set forth in claim 3 wherein a sub-frame of the residual signal is time shifted by time shift T only if a normalized correlation measurement G_opt is greater than or equal to a specified threshold value, wherein G_opt is defined as ##EQU9##

5. An improved method of speech coding as set forth in claim 4 wherein a sub-frame of the residual signal is time shifted by time shift T only if (a) G_opt is greater than or equal to a specified first threshold value, and (b) a peak-to-average ratio is greater than or equal to a specified second threshold value, wherein the peak-to-average ratio is defined as the ratio of the energy of a pulse in a sub-frame of the residual signal to the average energy of the residual signal in that sub-frame, thereby eliminating or reducing the undesired introduction of periodicity into non-periodic speech segments.