Apparatus and method for generating an adaptive spectral shape of comfort noise

• US 9,978,377 B2
• Filed: 12/18/2015
• Issued: 05/22/2018
• Est. Priority Date: 06/21/2013
• Status: Active Grant

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Original Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Inventors: Schnabel, Michael, Markovic, Goran, Sperschneider, Ralph, Lecomte, Jeremie, Helmrich, Christian
• Primary Examiner(s): Abebe, Daniel
• Application Number:
  US14/973,724
• Publication Number:
  US 20160104497A1
• Time in Patent Office: 886 Days
• Field of Search: 704500
• CPC Class Codes: G10L 19/002 Dynamic bit allocation for perceptual audio coders G10L19/032
• CPC Class Codes: G10L 19/005 Correction of errors induced by the transmission channel, if related to the coding algorithm
• CPC Class Codes: G10L 19/012 Comfort noise or silence coding
• CPC Class Codes: G10L 19/0212 using orthogonal transformation
• CPC Class Codes: G10L 19/06 Determination or coding of the spectral characteristics, e.g. of the short-term prediction coefficients
• CPC Class Codes: G10L 19/07 Line spectrum pair [LSP] vocoders
• CPC Class Codes: G10L 19/083 the excitation function being an excitation gain G10L25/90 takes precedence
• CPC Class Codes: G10L 19/09 Long term prediction, i.e. removing periodical redundancies, e.g. by using adaptive codebook or pitch predictor
• 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 19/22 Mode decision, i.e. based on audio signal content versus external parameters
• CPC Class Codes: G10L 2019/0002 Codebook adaptations
• CPC Class Codes: G10L 2019/0011 Long term prediction filters, i.e. pitch estimation
• CPC Class Codes: G10L 2019/0016 Codebook for LPC parameters

Abstract

An apparatus for decoding an encoded audio signal to obtain a reconstructed audio signal is provided, having: a receiving interface for receiving one or more frames, a coefficient generator, and a signal reconstructor. The coefficient generator is configured to determine one or more first audio signal coefficients, and one or more noise coefficients. Moreover, the coefficient generator is configured to generate one or more second audio signal coefficients, depending on the one or more first audio signal coefficients and depending on the one or more noise coefficients. The audio signal reconstructor is configured to reconstruct a first portion of the reconstructed audio signal depending on the one or more first audio signal coefficients and the audio signal reconstructor is configured to reconstruct a second portion of the reconstructed audio signal depending on the one or more second audio signal coefficients, if the current frame is not received by the receiving interface or if the current frame being received by the receiving interface is corrupted.

Claims

1. An apparatus for decoding an encoded audio signal to acquire a reconstructed audio signal, wherein the apparatus comprises:

a receiving interface for receiving one or more frames,

a coefficient generator, and

a signal reconstructor,

wherein the coefficient generator is configured to determine, if a current frame of the one or more frames is received by the receiving interface and if the current frame being received by the receiving interface is not corrupted, one or more first audio signal coefficients, being comprised by the current frame, wherein said one or more first audio signal coefficients indicate a characteristic of the encoded audio signal, and one or more noise coefficients indicating a spectral shape of a background noise of the encoded audio signal,

wherein the coefficient generator is configured to generate one or more second audio signal coefficients, depending on the one or more first audio signal coefficients and depending on the one or more noise coefficients, if the current frame is not received by the receiving interface or if the current frame being received by the receiving interface is corrupted,

wherein the audio signal reconstructor is configured to reconstruct a first portion of the reconstructed audio signal depending on the one or more first audio signal coefficients, if the current frame is received by the receiving interface and if the current frame being received by the receiving interface is not corrupted, and

wherein the audio signal reconstructor is configured to reconstruct a second portion of the reconstructed audio signal depending on the one or more second audio signal coefficients, if the current frame is not received by the receiving interface or if the current frame being received by the receiving interface is corrupted,

wherein the apparatus is implemented using a hardware apparatus or using a computer or using a combination of a hardware apparatus and a computer.

2. The apparatus according to claim 1, wherein the one or more first audio signal coefficients are one or more linear predictive filter coefficients of the encoded audio signal.

3. The apparatus according to claim 2, wherein the one or more linear predictive filter coefficients are represented by one or more immittance spectral pairs or by one or more line spectral pairs, or by one or more immittance spectral frequencies, or by one or more line spectral frequencies of the encoded audio signal.

4. The apparatus according to claim 1, wherein the one or more noise coefficients are one or more linear predictive filter coefficients indicating the background noise of the encoded audio signal.

5. The apparatus according to claim 2, wherein the one or more linear predictive filter coefficients represent a spectral shape of the background noise.

6. The apparatus according to claim 1, wherein the coefficient generator is configured to determine the one or more second audio signal portions such that the one or more second audio signal portions are one or more linear predictive filter coefficients of the reconstructed audio signal.

7. The apparatus according to claim 1,

wherein the coefficient generator is configured to generate the one or more second audio signal coefficients by applying the formula:

f_current[i]=α

·

f_last[i]+(1−

α

)·

pt_mean[i]

wherein f_current[i] indicates one of the one or more second audio signal coefficients,

wherein f_last[i] indicates one of the one or more first audio signal coefficients,

wherein pt_mean[i] is one of the one or more noise coefficients,

wherein α

is a real number with 0≤

α

≤

1, and

wherein i is an index.

8. The apparatus according to claim 7,

wherein f_last[i] indicates a linear predictive filter coefficient of the encoded audio signal, and

wherein f_current[i] indicates a linear predictive filter coefficient of the reconstructed audio signal.

9. The apparatus according to claim 8, wherein pt_mean[i] indicates the background noise of the encoded audio signal.

10. The apparatus according to claim 1, wherein the coefficient generator is configured to determine, if the current frame of the one or more frames is received by the receiving interface and if the current frame being received by the receiving interface is not corrupted, the one or more noise coefficients by determining a noise spectrum of the encoded audio signal.

11. The apparatus according to claim 1, wherein the coefficient generator is configured to determine LPC coefficients representing background noise by using a minimum statistics approach on the signal spectrum to determine a background noise spectrum and by calculating the LPC coefficients representing a background noise shape from the background noise spectrum.

12. A method for decoding an encoded audio signal to acquire a reconstructed audio signal, wherein the method comprises:

receiving one or more frames,

determining, if a current frame of the one or more frames is received and if the current frame being received is not corrupted, one or more first audio signal coefficients, being comprised by the current frame, wherein said one or more first audio signal coefficients indicate a characteristic of the encoded audio signal, and one or more noise coefficients indicating a spectral shape of a background noise of the encoded audio signal,

generating one or more second audio signal coefficients, depending on the one or more first audio signal coefficients and depending on the one or more noise coefficients, if the current frame is not received or if the current frame being received is corrupted,

reconstructing a first portion of the reconstructed audio signal depending on the one or more first audio signal coefficients, if the current frame is received and if the current frame being received is not corrupted, and

reconstructing a second portion of the reconstructed audio signal depending on the one or more second audio signal coefficients, if the current frame is not received or if the current frame being received is corrupted,

wherein the method is performed using a hardware apparatus or using a computer or using a combination of a hardware apparatus and a computer.

13. A non-transitory computer-readable medium comprising a computer program for implementing the method of claim 12 when being executed on a computer or signal processor.