Apparatus and method for improved signal fade out for switched audio coding systems during error concealment

• US 10,679,632 B2
• Filed: 01/24/2018
• Issued: 06/09/2020
• 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): Sirjani, Fariba
• Application Number:
  US15/879,287
• Publication Number:
  US 20180151184A1
• Time in Patent Office: 867 Days
• Field of Search: None
• 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 audio signal includes a receiving interface, wherein the receiving interface is configured to receive a first frame and a second frame. Moreover, the apparatus includes a noise level tracing unit for determining noise level information being represented in a tracing domain. Furthermore, the apparatus includes a first reconstruction unit for reconstructing a third audio signal portion of the audio signal depending on the noise level information and a second reconstruction unit for reconstructing a fourth audio signal portion depending on noise level information being represented in the second reconstruction domain.

Claims

1. An apparatus for decoding an audio signal, comprising:

a receiving interface for receiving a plurality of frames, wherein the receiving interface is configured to receive a first frame of the plurality of frames, said first frame comprising a first audio signal portion of the audio signal, said first audio signal portion being represented in a first domain, and wherein the receiving interface is configured to receive a second frame of the plurality of frames, said second frame comprising a second audio signal portion of the audio signal,

a transform unit for transforming the second audio signal portion or a value or signal derived from the second audio signal portion from a second domain to a tracing domain to acquire a second signal portion information, wherein the second domain is different from the first domain, wherein the tracing domain is different from the second domain, and wherein the tracing domain is equal to or different from the first domain,

a noise level tracing unit, wherein the noise level tracing unit is configured to receive a first signal portion information being represented in the tracing domain, wherein the first signal portion information depends on the first audio signal portion, wherein the noise level tracing unit is configured to receive the second signal portion being represented in the tracing domain, and wherein the noise level tracing unit is configured to determine noise level information depending on the first signal portion information being represented in the tracing domain and depending on the second signal portion information being represented in the tracing domain, wherein the noise level information is represented in the tracing domain.

2. The apparatus according to claim 1,

wherein the first audio signal portion is represented in a time domain as the first domain,

wherein the transform unit is configured to transform the second audio signal portion or the value derived from the second audio signal portion from an excitation domain being the second domain to the time domain being the tracing domain,

wherein the noise level tracing unit is configured to receive the first signal portion information being represented in the time domain as the tracing domain, and

wherein the noise level tracing unit is configured to receive the second signal portion being represented in the time domain as the tracing domain.

3. The apparatus according to claim 1,

wherein the first audio signal portion is represented in an excitation domain as the first domain,

wherein the transform unit is configured to transform the second audio signal portion or the value derived from the second audio signal portion from a time domain being the second domain to the excitation domain being the tracing domain,

wherein the noise level tracing unit is configured to receive the first signal portion information being represented in the excitation domain as the tracing domain, and

wherein the noise level tracing unit is configured to receive the second signal portion being represented in the excitation domain as the tracing domain.

4. The apparatus according to claim 1,

wherein the first audio signal portion is represented in an excitation domain as the first domain,

wherein the noise level tracing unit is configured to receive the first signal portion information, wherein said first signal portion information is represented in the FFT domain, being the tracing domain, and wherein said first signal portion information depends on said first audio signal portion being represented in the excitation domain,

wherein the transform unit is configured to transform the second audio signal portion or the value derived from the second audio signal portion from a time domain being the second domain to an FFT domain being the tracing domain, and

wherein the noise level tracing unit is configured to receive the second audio signal portion being represented in the FFT domain.

5. The apparatus according to claim 1,

wherein the apparatus further comprises a first aggregation unit for determining a first aggregated value depending on the first audio signal portion,

wherein the apparatus further comprises a second aggregation unit for determining, depending on the second audio signal portion, a second aggregated value as the value derived from the second audio signal portion,

wherein the noise level tracing unit is configured to receive the first aggregated value as the first signal portion information being represented in the tracing domain, wherein the noise level tracing unit is configured to receive the second aggregated value as the second signal portion information being represented in the tracing domain, and wherein the noise level tracing unit is configured to determine noise level information depending on the first aggregated value being represented in the tracing domain and depending on the second aggregated value being represented in the tracing domain.

6. The apparatus according to claim 5,

wherein the first aggregation unit is configured to determine the first aggregated value such that the first aggregated value indicates a root mean square of the first audio signal portion or of a signal derived from the first audio signal portion, and

wherein the second aggregation unit is configured to determine the second aggregated value such that the second aggregated value indicates a root mean square of the second audio signal portion or of a signal derived from the second audio signal portion.

7. The apparatus according to claim 1, wherein the transform unit is configured to transform the value derived from the second audio signal portion from the second domain to the tracing domain by applying a gain value on the value derived from the second audio signal portion.

8. The apparatus according to claim 7,

wherein the gain value indicates a gain introduced by Linear predictive coding synthesis, or

wherein the gain value indicates a gain introduced by Linear predictive coding synthesis and deemphasis.

9. The apparatus according to claim 1, wherein the noise level tracing unit is configured to determine noise level information by applying a minimum statistics approach.

10. The apparatus according to claim 1,

wherein the noise level tracing unit is configured to determine a comfort noise level as the noise level information, and

wherein the apparatus comprises a reconstruction unit being configured to reconstruct the third audio signal portion depending on the noise level information, if said third frame of the plurality of frames is not received by the receiving interface or if said third frame is received by the receiving interface but is corrupted.

11. The apparatus according to claim 9,

wherein the noise level tracing unit is configured to determine a comfort noise level as the noise level information derived from a noise level spectrum, wherein said noise level spectrum is acquired by applying the minimum statistics approach, and

wherein the apparatus comprises a reconstruction unit being configured to reconstruct the third audio signal portion depending on a plurality of Linear Predictive coefficients, if said third frame of the plurality of frames is not received by the receiving interface or if said third frame is received by the receiving interface but is corrupted.

12. The apparatus according to claim 1,

wherein the noise level tracing unit is configured to determine a plurality of FFT coefficients indicating a comfort noise level as the noise level information, and

wherein the apparatus comprises a reconstruction unit being configured to reconstruct the third audio signal portion depending on a comfort noise level derived from said FFT coefficients, if said third frame of the plurality of frames is not received by the receiving interface or if said third frame is received by the receiving interface but is corrupted.

13. The apparatus according to claim 1, wherein the apparatus comprises a reconstruction unit being configured to reconstruct the third audio signal portion depending on the noise level information and depending on the first or the second audio signal portion, if said third frame of the plurality of frames is not received by the receiving interface or if said third frame is received by the receiving interface but is corrupted.

14. The apparatus according to claim 13, wherein the reconstruction unit is configured to reconstruct the third audio signal portion by attenuating or amplifying a signal derived from the first audio signal portion or the second signal portion.

15. The apparatus according to claim 1,

wherein the apparatus further comprises a long-term prediction unit comprising a delay buffer,

wherein the long-term prediction unit is configured to generate a processed signal depending on the first or the second audio signal portion, depending on a delay buffer input being stored in the delay buffer and depending on a long-term prediction gain, and

wherein the long-term prediction unit is configured to fade the long-term prediction gain towards zero, if said third frame of the plurality of frames is not received by the receiving interface or if said third frame is received by the receiving interface but is corrupted.

16. The apparatus according to claim 15, wherein the long-term prediction unit is configured to fade the long-term prediction gain towards zero, wherein a speed with which the long-term prediction gain is faded towards zero depends on a fade-out factor.

17. The apparatus according to claim 15, wherein the long-term prediction unit is configured to update the delay buffer input by storing the generated processed signal in the delay buffer, if a third frame of the plurality of frames is not received by the receiving interface or if said third frame is received by the receiving interface but is corrupted.

18. The apparatus according to claim 1,

wherein the transform unit is a first transform unit,

wherein the apparatus comprises a first reconstruction unit,

wherein the apparatus further comprises a second transform unit and a second reconstruction unit,

wherein the second transform unit is configured to transform the noise level information from the tracing domain to the second domain, if a fourth frame of the plurality of frames is not received by the receiving interface or if said fourth frame is received by the receiving interface but is corrupted, and

wherein the second reconstruction unit is configured to reconstruct a fourth audio signal portion of the audio signal depending on the noise level information being represented in the second domain if said fourth frame of the plurality of frames is not received by the receiving interface or if said fourth frame is received by the receiving interface but is corrupted.

19. The apparatus according to claim 18, wherein the second reconstruction unit is configured to reconstruct the fourth audio signal portion depending on the noise level information and depending on the second audio signal portion.

20. The apparatus according to claim 19, wherein the second reconstruction unit is configured to reconstruct the fourth audio signal portion by attenuating or amplifying the second audio signal portion.

21. A method for decoding an audio signal, comprising:

receiving a first frame of a plurality of frames, said first frame comprising a first audio signal portion of the audio signal, said first audio signal portion being represented in a first domain,

receive a second frame of the plurality of frames, said second frame comprising a second audio signal portion of the audio signal,

transforming the second audio signal portion or a value or signal derived from the second audio signal portion from a second domain to a tracing domain to acquire a second signal portion information, wherein the second domain is different from the first domain, wherein the tracing domain is different from the second domain, and wherein the tracing domain is equal to or different from the first domain,

determining noise level information depending on first signal portion information, being represented in the tracing domain, and depending on the second signal portion information being represented in the tracing domain, wherein the first signal portion information depends on the first audio signal portion.

22. A non-transitory computer-readable medium comprising a computer program for implementing the method of claim 21 when being executed on a computer or signal processor.