Methods for improving high frequency reconstruction

• US 10,403,295 B2
• Filed: 08/18/2016
• Issued: 09/03/2019
• Est. Priority Date: 11/29/2001
• Status: Expired due to Term

• Current Assignee: Dolby International AB (Dolby Laboratories Incorporated)
• Original Assignee: Dolby International AB (Dolby Laboratories Incorporated)
• Inventors: Kjoerling, Kristofer, Ekstrand, Per, Hoerich, Holger
• Primary Examiner(s): Serrou, Abdelali
• Application Number:
  US15/240,727
• Publication Number:
  US 20160358616A1
• Time in Patent Office: 1,111 Days
• CPC Class Codes: G10L 19/0017 Lossless audio signal coding; Perfect reconstruction of coded audio signal by transmission of coding error G10L19/24 takes precedence
• CPC Class Codes: G10L 19/0204 using subband decomposition
• CPC Class Codes: G10L 19/0208 Subband vocoders
• 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 19/06 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 19/093 using sinusoidal excitation models
• CPC Class Codes: G10L 19/167 Audio streaming, i.e. formatting and decoding of an encoded audio signal representation into a data stream for transmission or storage purposes
• 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 19/26 Pre-filtering or post-filtering
• CPC Class Codes: G10L 19/265 Pre-filtering, e.g. high frequency emphasis prior to encoding
• CPC Class Codes: G10L 21/038 using band spreading techniques

Abstract

The present invention proposes a new method and a new apparatus for enhancement of audio source coding systems utilizing high frequency reconstruction (HFR). It utilizes a detection mechanism on the encoder side to assess what parts of the spectrum will not be correctly reproduced by the HFR method in the decoder. Information on this is efficiently coded and sent to the decoder, where it is combined with the output of the HFR unit.

Claims

1. Audio encoder for encoding an audio signal, comprising:

a processor configured for assessing, using a high frequency reconstruction method, within different frequency regions of the audio signal above a cross over frequency, where the high frequency reconstruction method does not, based on a frequency range of the audio signal below the cross over frequency, correctly generate a spectral line or spectral lines above the cross over frequency similar to a spectral line or spectral lines of the audio signal;

a line coder configured for coding the spectral line or the spectral lines above the cross over frequency, for the different frequency regions of the audio signal above the cross over frequency to obtain a coded spectral line or coded spectral lines for the different frequency regions of the audio signal above the cross over frequency; and

a transmitter configured for transmitting the coded spectral line or the coded spectral lines for the different frequency regions of the audio signal above the cross over frequency from the audio encoder to a decoder or to a memory for storing the coded spectral line or the coded spectral lines for the different frequency regions of the audio signal above the cross over frequency,

wherein one or more of the processor, the line coder and the transmitter is implemented, at least in part, by one or more hardware elements of the audio encoder.

2. The audio encoder of claim 1, wherein the line coder comprises a parametric coder or a waveform coder.

3. The audio encoder of claim 1, wherein the line coder is configured for generating a vector indicating for each band whether the band is to comprise a spectral line or not.

4. The audio encoder of claim 1, wherein the processor is configured for performing a high frequency reconstruction method for utilizing an available lowband of the audio signal to extrapolate a high band.

5. The audio encoder of claim 1, further comprising a filter bank configured for filtering the audio signal to obtain an audio signal representation for the different frequency regions.

6. The audio encoder of claim 5, wherein the filter bank is a complex valued filter bank.

7. Audio decoder for decoding an encoded audio signal, the encoded audio signal including a waveform encoded input signal representing a frequency content of an original audio signal below a predetermined frequency, and a coded spectral envelope and one or more parametrically coded spectral lines above the predetermined frequency, comprising:

a decoder that decodes the waveform encoded input signal to generate a plurality of core audio signal bands;

an envelope decoder that decodes the coded spectral envelope to generate a decoded spectral envelope;

a parametric decoder that decodes the parametrically coded spectral lines to generate parametrically decoded spectral lines above the predetermined frequency;

a high frequency reconstruction processor that receives the plurality of core audio signal bands and generates a reconstructed audio signal having a plurality of high frequency audio signal bands above the predetermined frequency,

wherein the high frequency reconstruction processor performs a bandwise processing to generate the plurality of high frequency audio signal bands, and comprises a synthesis filter bank that generates a decoded audio signal from different filter bank channels of the synthesis filter bank, and

wherein the high frequency reconstruction processor generates an input for at least one of the different filter bank channels of the synthesis filter bank by transposing the core audio signal bands and adjusting a spectral envelope of the transposed core audio signal bands in response to the decoded spectral envelope, and generates an input for at least one other of the different filter bank channels of the synthesis filter bank from the parametrically decoded spectral lines above the predetermined frequency,

wherein one or more of the high frequency reconstruction processor, and the synthesis filter bank is implemented, at least in part, by one or more hardware elements of the audio decoder.

8. The audio decoder of claim 7, wherein the high frequency reconstruction processor is configured to dynamically change the predetermined frequency being the cross over frequency separating the reconstructed audio signal from the core audio signal.

9. The audio decoder of claim 7, wherein the synthesis filter bank is a complex filter bank.

10. Method of encoding an audio signal, comprising:

assessing, using a high frequency reconstruction method, within different frequency regions of the audio signal above a cross over frequency, where the high frequency reconstruction method does not, based on a frequency range of the audio signal below the cross over frequency, correctly generate a spectral line or spectral lines similar to a spectral line or spectral lines of the audio signal above the cross over frequency;

coding the spectral line or the spectral lines above the cross over frequency, for the different frequency regions of the audio signal above the cross over frequency to obtain a coded spectral line or coded spectral lines for the different frequency regions of the audio signal above the cross over frequency; and

transmitting the coded spectral line or the coded spectral lines for the different frequency regions of the audio signal above the cross over frequency from an encoder to a decoder or storing the coded spectral line or the coded spectral lines for the different frequency regions of the audio signal above the cross over frequency,

wherein one or more of the assessing, the coding and the transmitting is implemented, at least in part, by one or more hardware elements of an audio signal processing device.

11. Non-transitory storage medium having stored thereon a computer program for performing, when running on a computer or processor, a method of encoding an audio signal, the method comprising:

assessing, using a high frequency reconstruction method, within different frequency regions of the audio signal above a cross over frequency, where the high frequency reconstruction method does not, based on a frequency range of the audio signal below the cross over frequency, correctly generate a spectral line or spectral lines similar to a spectral line or spectral lines of the audio signal above the cross over frequency;

coding the spectral line or the spectral lines above the cross over frequency, for the different frequency regions of the audio signal above the cross over frequency to obtain a coded spectral line or coded spectral lines for the different frequency regions of the audio signal above the cross over frequency; and

transmitting the coded spectral line or the coded spectral lines for the different frequency regions of the audio signal above the cross over frequency from an encoder to a decoder or storing the coded spectral line or the coded spectral lines for the different frequency regions of the audio signal above the cross over frequency.

12. A method of audio decoding an encoded audio signal, the encoded audio signal including a waveform encoded input signal representing a frequency content of an original audio signal below a predetermined frequency, and a coded spectral envelope and one or more parametrically coded spectral lines above the predetermined frequency, the method comprising:

decoding the waveform encoded input signal to generate a plurality of core audio signal bands;

decoding the coded spectral envelope to generate a decoded spectral envelope;

decoding the parametrically coded spectral lines to generate parametrically decoded spectral lines above the predetermined frequency;

receiving a plurality of core audio signal bands and generating a reconstructed audio signal having a plurality of high frequency audio signal bands above the predetermined frequency by a high frequency reconstruction processing comprising performing a bandwise processing to generate the plurality of high frequency audio signal bands, and comprising synthesis filtering, by a synthesis filter bank, for generating a decoded audio signal from different filter bank channels of the synthesis filter bank, and

wherein the high frequency reconstruction processing generates an input for at least one of the different filter bank channels of the synthesis filter bank by transposing the core audio signal bands and adjusting a spectral envelope of the transposed core audio signal bands in response to the decoded spectral envelope, and generates an input for at least one other of the different filter bank channels of the synthesis filter bank from the parametrically decoded spectral lines above the predetermined frequency,

wherein one or more of the receiving, and the synthesis filtering by a synthesis filter bank is implemented, at least in part, by one or more hardware elements of an audio signal pro-cessing device.

13. Non-transitory storage medium having stored thereon a computer program for performing, when running on a computer or processor, a method of audio decoding an encoded audio signal, the encoded signal including a waveform encoded input signal representing a frequency content of an original audio signal below a predetermined frequency, and a coded spectral envelope and one or more parametrically coded spectral lines above the predetermined frequency, the method comprising:

decoding the waveform encoded input signal to generate a plurality of core audio signal bands;

decoding the coded spectral envelope to generate a decoded spectral envelope;

decoding the parametrically coded spectral lines to generate parametrically decoded spectral lines above the predetermined frequency;

receiving a plurality of core audio signal bands and generating a reconstructed audio signal having a plurality of high frequency audio signal bands above the predetermined frequency by a high frequency reconstruction processing comprising performing a bandwise processing to generate the plurality of high frequency audio signal bands and comprising synthesis filtering for generating a decoded audio signal from different filter bank channels, and

wherein the high frequency reconstruction processing generates an input for at least one of the different filter bank channels by transposing the core audio signal bands and adjusting a spectral envelope of the transposed core audio signal bands in response to the decoded spectral envelope, and generates an input for at least one other of the different filter bank channels of the synthesis filter bank from the parametrically decoded spectral lines above the predetermined frequency.