Methods for Improving High Frequency Reconstruction

• US 20130226597A1
• Filed: 04/18/2013
• Published: 08/29/2013
• Est. Priority Date: 11/29/2001
• Status: Active Grant

• Current Assignee: Dolby International AB (Dolby Laboratories Incorporated)
• Original Assignee: Dolby International AB (Dolby Laboratories Incorporated)
• Inventors: KJOERLING, Kristofer, EKSTRAND, Per, HOERICH, Holger
• Granted Patent: US 9,431,020 B2
• Time in Patent Office: Days
• US Class Current: 704/500
• 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 utilising high frequency reconstruction (HFR). It utilises 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 for assessing, using a high frequency reconstruction method, within different frequency regions, where the high frequency reconstruction method does not, based on the frequency range below a cross over frequency, correctly generate a spectral line or spectral lines similar to a spectral line or spectral lines of the audio signal;

a line coder for coding the spectral line or the spectral lines, for the different frequency regions; and

a transmitter for transmitting the coded spectral line or spectral lines for the different frequency regions from the encoder to a decoder or a memory for storing the coded spectral line or spectral lines for the different frequency regions.

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 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 comprising one or more coded spectral lines, comprising:

a line decoder for decoding the one or more coded spectral lines;

an adder for adding the decoded one or more spectral lines to different frequency regions of an output of a high frequency reconstruction processing to obtain a decoded audio signal.

8. The audio decoder of claim 7, wherein the line decoder comprises a parametric decoding of the one or more coded spectral lines or a waveform decoding of the one or more coded spectral lines.

9. The audio decoder of claim 7, further comprising a subband filter bank for synthesizing the decoded one or more spectral lines.

10. The audio decoder of claim 7, further comprising a core decoder for generating a decoded core audio signal, and wherein the subband filterbank is configured for synthesising the decoded one or more spectral lines together with the decoded core audio signal.

11. Audio decoder for decoding an encoded audio signal, the encoded signal including an encoded input signal representing a frequency content of an original audio signal below a predetermined frequency, comprising:

a high frequency reconstruction processor for receiving a plurality of core audio signal bands and for generating a reconstructed signal having a frequency above the predetermined frequency,

wherein the high frequency reconstruction processor is configured for performing a bandwise processing and comprises a synthesis filter bank for generating a decoded audio signal from different filter bank channels, and

wherein the audio decoder is configured for selecting an input for different filter bank channels from one or more of the following sources;

waveform coding;

transposition;

parametric coding; and

any other coding or reconstruction method applicable in certain parts of a spectrum.

12. Audio decoder of claim 11, wherein the waveform coding comprises coding using a core coder or additional coding beyond a Nyquist frequency, or wherein the transposition comprises a following envelope adjustment.

13. Method of encoding an audio signal, comprising:

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

coding the spectral line or the spectral lines, for the different frequency regions; and

transmitting the coded spectral line or spectral lines for the different frequency regions from an encoder to a decoder or storing the coded spectral line or spectral lines for the different frequency regions.

14. 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, where the high frequency reconstruction method does not, based on the frequency range below a cross over frequency, correctly generate a spectral line or spectral lines similar to a spectral line or spectral lines of the audio signal;

coding the spectral line or the spectral lines, for the different frequency regions; and

transmitting the coded spectral line or spectral lines for the different frequency regions from an encoder to a decoder or storing the coded spectral line or spectral lines for the different frequency regions.

15. Method of audio decoding an encoded audio signal comprising one or more coded spectral lines, comprising:

decoding the one or more coded spectral lines; and

adding the decoded one or more spectral lines to different frequency regions of an output of a high frequency reconstruction processing to obtain a decoded audio signal.

16. 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 comprising one or more coded spectral lines, the method comprising:

decoding the one or more coded spectral lines; and

adding the decoded one or more spectral lines to different frequency regions of an output of a high frequency reconstruction processing to obtain a decoded audio signal

17. A method of audio decoding an encoded audio signal, the encoded signal including an encoded input signal representing a frequency content of an original audio signal below a predetermined frequency, comprising:

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

wherein an input for different filter bank channels is selected from one or more of the following sources;

waveform coding;

transposition;

parametric coding; and

any other coding or reconstruction method applicable in certain parts of a spectrum.