Adaptive Transition Frequency Between Noise Fill and Bandwidth Extension

• US 20160086614A1
• Filed: 12/01/2015
• Published: 03/24/2016
• Est. Priority Date: 08/27/2007
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Briand, Manuel, Taleb, Anisse, ULLBERG, Gustaf
• Granted Patent: US 9,711,154 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G10L 19/0204 using subband decomposition
• CPC Class Codes: G10L 19/028 Noise substitution, i.e. substituting non-tonal spectral components by noisy source comfort noise for discontinuous speech transmission G10L19/012
• CPC Class Codes: G10L 19/032 Quantisation or dequantisation of spectral components
• CPC Class Codes: G10L 19/035 Scalar quantisation
• CPC Class Codes: G10L 21/038 using band spreading techniques

Abstract

A method for spectrum recovery in spectral decoding of an audio signal, comprises obtaining of an initial set of spectral coefficients representing the audio signal, and determining 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 and the initial set of spectral coefficients are bandwidth extended above the transition frequency. Decoders and encoders being arranged for performing part of or the entire method are also illustrated.

Claims

1. A method for spectrum recovery for spectral decoding of an audio signal, comprising the steps of:

obtaining an initial set of spectral coefficients representing said audio signal;

dividing said spectral coefficients of said initial set of spectral coefficients into a plurality of frequency bands;

determining a transition frequency;

noise filling of spectral holes in said initial set of spectral coefficients below said transition frequency; and

bandwidth extending said initial set of spectral coefficients above said transition frequency;

wherein

said transition frequency is set at the upper limit of the first frequency band seen from the high-frequency side that has a quantized coefficient in it.

2. The method according to claim 1, wherein said frequency bands have a constant frequency width.

3. The method according to claim 1, wherein at least two of said frequency bands have different frequency widths.

4. The method according to claim 1, wherein said step of setting said transition frequency is further dependent on a previously used transition frequency.

5. The method according to claim 4, wherein said step of setting said transition frequency is further dependent on more than one previously used transition frequency.

6. The method according to claim 5, wherein said transition frequency is prohibited to change more than a predetermined absolute or relative amount between two consecutive frames.

7. A method for use for spectral coding of an audio signal, comprising:

dividing spectral coefficients of an initial set of spectral coefficients representing said audio signal into a plurality of frequency bands; and

determining a transition frequency for the initial set of spectral coefficients representing said audio signal, wherein

said transition frequency defines a border between a first frequency range intended to be a subject for noise filling of spectral holes and a second frequency range intended to be a subject for bandwidth extension, and

said transition frequency is set at the upper limit of the first frequency band seen from the high-frequency side that has a quantized coefficient in it.

8. A decoder apparatus for spectral decoding of an audio signal, comprising:

an input for obtaining an initial set of spectral coefficients representing said audio signal;

a transition determining circuitry arranged for determining a transition frequency;

a noise filler for noise filling of spectral holes in said initial set of spectral coefficients below said transition frequency; and

a bandwidth extender arranged for bandwidth extending said initial set of spectral coefficients above said transition frequency, wherein

said transition determining circuitry is arranged for;

dividing said spectral coefficients of said initial set of spectral coefficients into a plurality of frequency bands, and

determining said transition frequency as the upper limit of the first frequency band seen from the high-frequency side that has a quantized coefficient in it.

9. An encoder apparatus for spectral coding of an audio signal, comprising:

transition determining circuitry arranged for determining a transition frequency for an initial set of spectral coefficients representing said audio signal, said transition frequency defining a border between a first frequency range intended to be a subject for noise filling of spectral holes and a second frequency range intended to be a subject for bandwidth extension, wherein said transition determining circuitry is arranged for;

dividing said spectral coefficients of said initial set of spectral coefficients into a plurality of frequency bands, and

determining said transition frequency as the upper limit of the first frequency band seen from the high-frequency side that has a quantized coefficient in it.