Concealment of frame erasures and method

• US 20020123887A1
• Filed: 02/27/2002
• Published: 09/05/2002
• Est. Priority Date: 02/27/2001
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Unno, Takahiro
• Granted Patent: US 7,587,315 B2
• Time in Patent Office: Days
• US Class Current: 704/220
• CPC Class Codes: G10L 19/005 Correction of errors induced by the transmission channel, if related to the coding algorithm
• CPC Class Codes: G10L 19/12 the excitation function being a code excitation, e.g. in code excited linear prediction [CELP] vocoders
• CPC Class Codes: G10L 2019/0011 Long term prediction filters, i.e. pitch estimation
• CPC Class Codes: G10L 2019/0012 Smoothing of parameters of the decoder interpolation
• CPC Class Codes: G10L 2025/935 Mixed voiced class; Transitions

Abstract

A decoder for code excited LP encoded frames with both adaptive and fixed codebooks; erased frame concealment uses repetitive excitation plus a smoothing of pitch gain in the next good frame, plus multilevel voicing classification with multiple thresholds of correlations determining linear interpolated adaptive and fixed codebook excitation contributions.

Claims

1. A method for decoding code-excited linear prediction signals, comprising:

(a) forming an excitation for an erased interval of encoded code-excited linear prediction signals by a weighted sum of (i) an adaptive codebook contribution and (ii) a fixed codebook contribution, wherein said adaptive codebook contribution derives from an excitation and pitch and first gain of one or more intervals prior to said erased interval and said fixed codebook contribution derives from a second gain of at least one of said prior intervals;

(b) wherein said weighted sum has sets of weights depending upon a periodicity classification of at least one prior interval of encoded signals, said periodicity classification with at least three classes; and

(c) filtering said excitation.

2. The method of claim 1, wherein:

(a) said filtering includes a synthesis with synthesis filter coefficients derived from filter coefficients of said intervals prior in time.

3. A method for decoding code-excited linear prediction signals, comprising:

(a) forming a reconstruction for an erased interval of encoded code-excited linear prediction signals by use parameters of one or more intervals prior to said erased interval;

(b) preliminarily decoding a second interval subsequent to said erased interval;

(c) combining the results of step (b) with said parameters of step (a) to form a reestimation of parameters for said erased interval; and

(d) using the results of step (c) as part of an excitation for said second interval.

4. The method of claim 3, further comprising:

(a) said step (c) of claim 3 includes smoothing a gain.

5. A decoder for CELP encoded signals, comprising:

(a) a fixed codebook vector decoder;

(b) a fixed codebook gain decoder;

(c) an adaptive codebook gain decoder;

(d) an adaptive codebook pitch delay decoder;

(e) an excitation generator coupled to said decoders; and

(f) a synthesis filter;

(g) wherein when a received frame is erased, said decoders generate substitute outputs, said excitation generator generates a substitute excitation, said synthesis filter generates substitute filter coefficients, and said excitation generator uses a weighted sum of (i) an adaptive codebook contribution and (ii) a fixed codebook contribution with said weighted sum uses sets of weights depending upon a periodicity classification of at least one prior frame, said periodicity classification with at least three classes;

6. A decoder for CELP encoded signals, comprising:

(a) a fixed codebook vector decoder;

(b) a fixed codebook gain decoder;

(c) an adaptive codebook gain decoder;

(d) an adaptive codebook pitch delay decoder;

(e) an excitation generator coupled to said decoders; and

(f) a synthesis filter;

(g) wherein when a received frame is erased, said decoders generate substitute outputs, said excitation generator generates a substitute excitation, said synthesis filter generates substitute filter coefficients, and when a second frame is received after said erased frame, said excitation generator combines parameters of said second frame with said substitute outputs to reestimate said substitute outputs to form an excitation for said second frame.