US 5,651,091 AGranted

Method and apparatus for low-delay CELP speech coding and decoding

AssigneeLucent Technologies Inc.

InventorJuin-Hwey Chen

Life of this patent

Estimating the term…

Abstract

A low-bitrate (typically 8 kbit/s or less), low-delay digital coder and decoder based on Code Excited Linear Prediction for speech and similar signals features backward adaptive adjustment for codebook gain and short-term synthesis filter parameters and forward adaptive adjustment of long-term (pitch) synthesis filter parameters. A highly efficient, low delay pitch parameter derivation and quantization permits overall delay which is a fraction of prior coding delays for equivalent speech quality at low bitrates.

Claims13

Dependent claims

A method of coding a frame of sampled input speech with a coder, the coder comprising a source of excitation signals, a gain scaler, a long term filter, and a short term filter, the source of excitation signals comprising a plurality of excitation sequences, the method comprising the steps of:

(a) multiplying an excitation sequence from the plurality of excitation sequences by a gain factor contained in the gain scaler to generate a gain adjusted excitation sequence;
(b) filtering the gain adjusted excitation sequence with the long term filter and the short term filter to generate a synthesized speech vector;
(c) comparing the synthesized speech vector with the frame of sampled input speech to generate an error signal;
(d) repeating steps (a) through (c) for each excitation sequence of the plurality of excitation sequences remaining to generate a set of remaining error signals, a set of error signals comprising the set of remaining error signals and the error signal;
(e) determining an index corresponding to an excitation sequence whose synthesized speech vector substantially approximates, based upon the set of error signals, the frame of sampled input speech;
(f) generating a pitch signal representative of a differentially coded pitch period, the differentially coded pitch period being representative of the difference between a pitch period of the frame and a pitch period prediction of the frame, the pitch period prediction being representative of at least one pitch period of a previous portion of sampled input speech, wherein the step of generating the pitch signal comprises
(i) applying a pitch detector to the frame to generate a preliminary quantized pitch estimate for the frame, and
(ii) generating the pitch signal by selectively applying a closed-loop optimization scheme employing a codebook search, said selective application of said closed-loop optimization scheme based on said preliminary quantized pitch estimate, and
(g) coding the frame with use of the determined index and the generated pitch signal.

6 more elements

Dependencies are inferred from the claim text.

Facts

Application: 08/057,068Filed 3 May 1993 · continuation
Priority: 10 Sep 1991
Granted: 22 Jul 1997
Term ends: Not estimatedThe source records don’t support an estimate.

Classification13 codes

G10L 19/18
Vocoder architecture: vocoders using multiple modes
G10L 19/08
Using predictive techniques: determination or coding of the excitation function; Determination or coding of the long-term prediction parameters
G10L 19/12
Determination or coding of the excitation function; Determination or coding of the long-term prediction parameters: the excitation function being…
G10L 19/26
Using predictive techniques: pre-filtering or post-filtering

Family

Serial757,168Parent of this continuation · filed 10 Sep 1991
US 5,233,660 AParent of this continuation
US 5,651,091 AThis patent

From the US filing history. Foreign family members aren’t listed.

Timeline

Citations

Open elsewhere

patentgrep

Loading patent…

Abstract

(a) multiplying an excitation sequence from the plurality of excitation sequences by a gain factor contained in the gain scaler to generate a gain adjusted excitation sequence;
(b) filtering the gain adjusted excitation sequence with the long term filter and the short term filter to generate a synthesized speech vector;
(c) comparing the synthesized speech vector with the frame of sampled input speech to generate an error signal;
(d) repeating steps (a) through (c) for each excitation sequence of the plurality of excitation sequences remaining to generate a set of remaining error signals, a set of error signals comprising the set of remaining error signals and the error signal;
(e) determining an index corresponding to an excitation sequence whose synthesized speech vector substantially approximates, based upon the set of error signals, the frame of sampled input speech;
(f) generating a pitch signal representative of a differentially coded pitch period, the differentially coded pitch period being representative of the difference between a pitch period of the frame and a pitch period prediction of the frame, the pitch period prediction being representative of at least one pitch period of a previous portion of sampled input speech, wherein the step of generating the pitch signal comprises
(i) applying a pitch detector to the frame to generate a preliminary quantized pitch estimate for the frame, and
(ii) generating the pitch signal by selectively applying a closed-loop optimization scheme employing a codebook search, said selective application of said closed-loop optimization scheme based on said preliminary quantized pitch estimate, and
(g) coding the frame with use of the determined index and the generated pitch signal.

6 more elements

Facts

Application

08/057,068Filed 3 May 1993 · continuation

Priority

10 Sep 1991

Granted

22 Jul 1997

Term ends

Not estimatedThe source records don’t support an estimate.

Classification13 codes

G10L 19/18
Vocoder architecture: vocoders using multiple modes
G10L 19/08
Using predictive techniques: determination or coding of the excitation function; Determination or coding of the long-term prediction parameters
G10L 19/12
Determination or coding of the excitation function; Determination or coding of the long-term prediction parameters: the excitation function being…
G10L 19/26
Using predictive techniques: pre-filtering or post-filtering