Adaptive transition frequency between noise fill and bandwidth extension

Patent metadata

Field	Value
Publication number	US-9269372-B2
Application number	US-67434108-A
Country	US
Kind code	B2
Filing date	Aug 26, 2008
Priority date	Aug 27, 2007
Publication date	Feb 23, 2016
Grant date	Feb 23, 2016

Abstract

A method for spectrum recovery in spectral decoding of an audio signal, comprises obtaining ( 210 ) of an initial set of spectral coefficients representing the audio signal, and determining ( 212 ) a transition frequency. The transition frequency is adapted to a spectral content of the audio signal. Spectral holes in the initial set of spectral coefficients below the transition frequency are noise filled ( 214 ) and the initial set of spectral coefficients are bandwidth extended ( 216 ) above the transition frequency. Decoders and encoders being arranged for performing part of or the entire method are also illustrated.

First claim

The invention claimed is:

1. A method for spectrum recovery in spectral decoding of an audio signal, the audio signal comprising a set of frames including a first frame and a second frame, the method comprising the steps of:
an audio decoding apparatus obtaining a first set of spectral coefficients representing only said first frame of said audio signal;
the audio decoding apparatus determining a first transition frequency (f t ) for said first frame of said audio signal;
the audio decoding apparatus determining a second transition frequency (f t2 ) for said second frame of said audio signal;
the audio decoding apparatus noise filling of spectral holes in said first set of spectral coefficients below said first transition frequency (f t ); and
the audio decoding apparatus bandwidth extending said first set of spectral coefficients above said transition frequency (f t ), wherein
determining said first transition frequency (f t ) comprises selecting said first transition frequency (f t ) based on a distribution of spectral holes in said first set of spectral coefficients representing only said first frame of said audio signal.

2. The method according to claim 1 , wherein said step of selecting said transition frequency (f t ) comprises the steps of:
dividing said spectral coefficients of said first set of spectral coefficients into a plurality of frequency bands, including a highest frequency band;
determining the number of coded spectral coefficients or groups within the highest frequency band;
dividing the determined number by a determined total number of spectral coefficients to produce a proportion value; and
determining whether the proportion value is not less than a threshold.

3. The method according to claim 2 , wherein said frequency bands have a constant frequency width.

4. The method according to claim 2 , wherein at least two of said frequency bands have different frequency widths.

5. The method according to claim 2 , wherein said step of selecting said transition frequency (f t ) further comprises:
finding a transition frequency band, being a highest frequency band in which said proportion is lower than a first threshold.

6. The method according to claim 5 , wherein said step of selecting said transition frequency (f t ) further comprises:
setting said transition frequency (f t ) dependent on an upper frequency limit of said transition frequency band.

7. The method according to claim 1 , wherein said step of determining said first transition frequency (f t ) comprises selecting said first transition frequency (f t ) based on i) the distribution of spectral holes in said first set of spectral coefficients and ii) a previously used transition frequency for a frame of the audio signal that is previous to said first frame of the audio signal.

8. The method according to claim 7 , wherein said transition frequency (f t ) is prohibited to change more than a predetermined absolute or relative amount between two consecutive frames.

9. The method according to claim 1 , wherein said step of determining said first transition frequency (f t ) comprises selecting said first transition frequency (f t ) based on the distribution of spectral holes in said first set of spectral coefficients, a first previously used transition frequency for a first previous frame that is previous to said first frame, and a second previously used transition frequency for a second previous frame that is previous to said first previous frame.

10. The method of claim 1 , further comprising:
an audio decoding apparatus obtaining a second set of spectral coefficients representing only said second frame of said audio signal;
the audio decoding apparatus noise filling of spectral holes in said second set of spectral coefficients below said second transition frequency (f t2 ); and
the audio decoding apparatus bandwidth extending said second set of spectral coefficients above said transition frequency (f t2 ).

11. A method for use in spectral coding of an audio signal, the audio signal comprising a set of frames including a first frame and a second frame, the method comprising:
an encoding apparatus receiving the first frame of the audio signal;
the encoding apparatus receiving the second frame of the audio signal;
the encoding apparatus producing a binary flux comprising first data representing the first frame of the audio signal and second data representing the second frame of the audio signal; and
transmitting the binary flux towards a decoder apparatus, wherein
producing the binary flux comprises: i) the encoding apparatus producing a first set of spectral coefficients representing only said first frame of said audio signal, said first set of spectral coefficients having a first set of spectral holes; ii) the encoding apparatus determining a distribution of spectral holes in said first set of spectral coefficients; iii) the encoding apparatus determining a first transition frequency (f t1 ) for the first set of spectral coefficients based on the distribution of the spectral holes in said first set of spectral holes, iv) the encoding apparatus producing a second set of spectral coefficients representing only said second frame of said audio signal, said second set of spectral coefficients having a second set of spectral holes; v) the encoding apparatus determining a distribution of spectral holes in said second set of spectral coefficients; vi) the encoding apparatus determining a second transition frequency (f t2 ) for the second set of s spectral coefficients based on the distribution of the spectral holes in said second set of spectral holes,
said first transition frequency (f t1 ) defines a border between a frequency range, intended to be a subject for noise filling of spectral holes, and a frequency range, intended to be a subject for bandwidth extension, and
said second transition frequency (f t2 ) defines a border between a frequency range, intended to be a subject for noise filling of spectral holes, and a frequency range, intended to be a subject for bandwidth extension.

12. The method of claim 11 , wherein determining the transition frequency (f t ) for the first set of spectral coefficients based on the distribution of the spectral holes comprises:
dividing said spectral coefficients of said first set of spectral coefficients into a plurality of frequency bands, including a highest frequency band;
determining the number of coded spectral coefficients or groups within the highest frequency band;
dividing the determined number by a determined total number of spectral coefficients to produce a proportion value; and
determining whether the proportion value is not less than a threshold.

13. The method of claim 11 , wherein the encoding apparatus determines the transition frequency (f t ) for the first set of spectral coefficients based not only on the distribution of the spectral holes but also on a previously determined transition frequency for a previous frame of the audio signal that is previous to said first frame of the audio signal.

14. A decoder apparatus for spectral decoding of an audio signal, the audio signal comprising a set of frames including a first frame and a second frame, the decoder apparatus comprising:
input for obtaining a first set of spectral coefficients representing only said first frame of said audio signal;
transition determining circuitry arranged for determining a first transition frequency (f t1 ) for said first frame of said audio signal and a second transition frequency (f t2 ) for said second frame of said audio signal;
a noise filler for noise filling of spectral holes in said first set of spectral

Assignees

• Ullberg Gustaf
• Taleb Anisse
• Briand Manuel
• Ericsson Telefon Ab L M

Inventors

• Ullberg Gustaf
• Taleb Anisse
• Briand Manuel

Classifications

• G10L19/032

  Quantisation or dequantisation of spectral components · CPC title

• G10L19/028 Primary

  Noise substitution, i.e. substituting non-tonal spectral components by noisy source (comfort noise for discontinuous speech transmission G10L19/012) · CPC title

• G10L19/035

  Scalar quantisation · CPC title

• G10L19/0204

  using subband decomposition · CPC title

• G10L21/038 Primary

  using band spreading techniques · CPC title