Methods and apparatus for coding digital audio signals using a filtered quantizing noise

• US 8,719,012 B2
• Filed: 06/13/2008
• Issued: 05/06/2014
• Est. Priority Date: 06/15/2007
• Status: Active Grant

• Current Assignee: Orange S.A.
• Original Assignee: Orange S.A.
• Inventors: Kovesi, Balazs, Le Guyader, Alain, Ragot, Stphane
• Primary Examiner(s): Godbold, Douglas
• Application Number:
  US12/602,809
• Publication Number:
  US 20100145712A1
• Time in Patent Office: 2,153 Days
• Field of Search: 704200-201, 704226-228
• US Class Current: 704/227
• CPC Class Codes: G10L 19/032 Quantisation or dequantisation of spectral components
• CPC Class Codes: G10L 19/24 Variable rate codecs, e.g. for generating different qualities using a scalable representation such as hierarchical encoding or layered encoding
• CPC Class Codes: G10L 19/265 Pre-filtering, e.g. high frequency emphasis prior to encoding
• CPC Class Codes: H04B 14/04 using pulse code modulation

Abstract

The invention concerns an encoder for an input audio signal (S(z)) comprising a combination module combining the input audio signal with an intermediate counter-reaction signal forming a modified input signal and a quantification module scalable for the rate (91) of said modified input signal, delivering a binary raster of quantification indexes of a predetermined rate. This encoder is such that it comprises: a reverse quantification module (93) of a part of the quantification indexes of the binary raster corresponding to the indexes of a rate lower than the predetermined rate, for predetermining a reconstructed signal (S_Mic(z)), a module for determining (94) a quantification noise (Q_Mic(z)) derived from at least quantification modules and reverse quantification modules in series, a determination module (111) for a filtering function of the quantification noise from said reconstructed signal and a filtering module fit for applying (33) said filtering function to said quantification noise in order to obtain said intermediary counter-reaction signal. The invention also relates to an encoding method applied by the described encoder and a corresponding decoding method applied by a decoder.

Claims

1. A method of coding an input audio signal comprising the steps:

combining said input audio signal with an intermediate feedback signal forming a modified input signal;

quantizing said modified input signal;

delivering a quantizing index binary frame of a predetermined bit rate;

inverse quantizing of some of the quantizing indices of the binary frame corresponding to the indices of a core bit rate lower than the predetermined bit rate, to determine a core bit rate reconstructed signal;

determining quantizing noise generated at least by the succession of the quantizing step and the inverse quantizing step;

determining a quantizing noise filter function from said core bit rate reconstructed signal; and

applying said filter function to said quantizing noise to obtain said intermediate feedback signal.

2. The method as claimed in claim 1, wherein the quantizing step provides at least core bit rate quantizing indices corresponding to PCM coding type core coding.

3. The method as claimed in claim 1, wherein said intermediate feedback signal is calculated from a prediction of the quantizing noise and a prediction of the filtered quantizing noise, the filtered quantizing noise being obtained by adding the intermediate signal and the quantizing noise.

4. The method as claimed in claim 1, wherein the quantizing noise filter function is furthermore calculated from periodicity characteristics of the input signal.

5. The method as claimed in claim 1, wherein the scalable quantizing step of predetermined bit rate is a PCM scalar quantizing step, the inverse quantizing step of the indices of a core bit rate lower than the predetermined bit rate applies to 8-K bits of the binary frame to determine a core bit rate reconstructed signal, and there is also effected a step of inserting K data bits.

12. A computer program stored in a memory of a coder or a decoder or on a memory medium adapted to cooperate with a reader of the coder or the decoder, said computer program comprising code instructions for executing the steps of the coding method as claimed in claim 1 when said program is executed by a processor of the coder or the decoder.

6. A method for scalable decoding of an audio signal, said method comprising:

a first step of inverse quantization decoding quantizing indices of a core bit rate to form a core bit rate reconstructed signal;

a second step of inverse quantization decoding quantizing indices of a second bit rate higher than the core bit rate, executed as a function of the bit rate received on decoding, to form a reconstructed signal of higher bit rate;

a third step of obtaining a difference signal between said core bit rate reconstructed signal and said higher bit rate reconstructed signal;

a fourth step of determining a correction filter function from the core bit rate reconstructed signal;

a filtering step capable of applying said correction filter function to said difference signal to obtain a corrective term;

a fifth step of synthesizing a corrected reconstructed signal at higher bit rate capable of combining said corrective term and one of the reconstructed signals.

7. The method as claimed in claim 6, wherein said corrective term is applied to said core bit rate reconstructed signal.

8. The method as claimed in claim 6, wherein said corrective term is applied to said higher bit rate reconstructed signal.

9. A decoding method as claimed in claim 6, further comprising a step of receiving information regarding insertion of bits on coding and, in the case of insertion information on K bits, a step of masking the K bits inserted is effected before the first step of core bit rate inverse quantization.

13. A computer program stored in a memory of a coder or a decoder or on a memory medium adapted to cooperate with a reader of the coder or the decoder, said computer program comprising code instructions for executing the steps of the decoding method as claimed in claim 6 when said program is executed by a processor of the coder or the decoder.

10. An input audio signal coder comprising a combination module combining the input audio signal with an intermediate feedback signal to form a modified input signal and a bit rate scalable quantizing module for quantizing said modified input signal to deliver a binary frame of quantizing indices of predetermined bit rate, said input audio signal coder further comprising:

a module for inverse quantization of some of the quantizing indices of the binary frame corresponding to the indices of a core bit rate lower than the predetermined bit rate, to determine a core bit rate reconstructed signal;

a module for determining a quantizing noise generated at least by the succession of the quantizing step and the inverse quantizing step;

a module for determining a quantizing noise filter function from said core bit rate reconstructed signal;

a module for applying said filter function to said quantizing noise to obtain said intermediate feedback signal.

11. An audio signal decoder comprising:

a first module for inverse quantization decoding quantizing indices at core bit rate to form a core bit rate reconstructed signal;

a second module for inverse quantization decoding quantizing indices at a second bit rate higher than the core bit rate, executed as a function of the bit rate received on decoding, to form a reconstructed signal of higher bit rate;

a module for obtaining a difference signal between said core bit rate reconstructed signal and said higher bit rate reconstructed signal;

a module for determining a correction filter function from the core bit rate reconstructed signal;

a module for applying said correction filter function to said difference signal to obtain a corrective term;

a module for synthesizing a corrected reconstructed signal at higher bit rate by combining said corrective term and one of the reconstructed signals.