Cross product enhanced harmonic transposition

Patent metadata

Field	Value
Publication number	US-2024194211-A1
Application number	US-202418439631-A
Country	US
Kind code	A1
Filing date	Feb 12, 2024
Priority date	Jan 16, 2009
Publication date	Jun 13, 2024
Grant date	—

Abstract

The present invention relates to audio coding systems which make use of a harmonic transposition method for high frequency reconstruction (HFR). A system and a method for generating a high frequency component of a signal from a low frequency component of the signal is described. The system comprises an analysis filter bank providing a plurality of analysis subband signals of the low frequency component of the signal. It also comprises a non-linear processing unit to generate a synthesis subband signal with a synthesis frequency by modifying the phase of a first and a second of the plurality of analysis subband signals and by combining the phase-modified analysis subband signals. Finally, it comprises a synthesis filter bank for generating the high frequency component of the signal from the synthesis subband signal.

First claim

1 . A system for decoding an audio signal, the system comprising:
a core decoder for decoding a low frequency component of the audio signal; an analysis filter bank for providing a plurality of analysis subband signals of the low frequency component of the audio signal; a subband selection reception unit for receiving information associated with a fundamental frequency Ω of the audio signal, and for selecting, in response to the information, a first analysis subband signal and a second analysis subband signal from the plurality of analysis subband signals; a non-linear processing unit to generate a synthesis subband signal from the first analysis subband signal and the second analysis subband signal, wherein a magnitude of the synthesis subband signal is based on a gain adjusted mean value of magnitudes of the first and second analysis subband signals, and a phase of the synthesis subband signal is based on a weighted sum of phases of the first and second analysis subband signals, wherein weighting factors applied to the phases of the first and second analysis subband signals are integers; and a synthesis filter bank for generating a high frequency component of the audio signal from the synthesis subband signal; wherein the information associated with the fundamental frequency Ω of the audio signal is received in an encoded bit stream.

2 . The system according to claim 1 , wherein
the analysis filter bank has N analysis subbands at an essentially constant subband spacing of Δω; an analysis subband is associated with an analysis subband index n, with n∈{1, . . . , N}; the synthesis filter bank has a synthesis subband; the synthesis subband is associated with a synthesis subband index n; and the synthesis subband and the analysis subband with index n each comprise frequency ranges which relate to each other through a factor T.

3 . The system according to claim 2 , further comprising:
an analysis window, which isolates a pre-defined time interval of the low frequency component around a pre-defined time instance k; and a synthesis window, which isolates a pre-defined time interval of the high frequency component around the pre-defined time instance k.

4 . The system according to claim 3 , wherein the synthesis window is a time-scaled version of the analysis window.

5 . The system according to claim 1 , further comprising:
an upsampler for performing an upsampling of the low frequency component to yield an upsampled low frequency component; an envelope adjuster to shape the high frequency component; and a component summing unit to determine a decoded audio signal as the sum of the upsampled low frequency component and the adjusted high frequency component.

6 . The system according to claim 5 , further comprising an envelope reception unit for receiving information related to the envelope of the high frequency component of the audio signal.

7 . The system according to claim 6 , further comprising:
an input unit for receiving the audio signal, comprising the low frequency component; and an output unit for providing the decoded audio signal, comprising the low and the generated high frequency component.

8 . The system according to claim 1 , wherein the non-linear processing unit comprises a multiple-input-single-output unit of a first and second transposition order for generating the synthesis subband signal with a synthesis frequency from the first and the second analysis subband signals with a first and a second analysis frequency, respectively; wherein the synthesis frequency corresponds to the first analysis frequency multiplied by the first transposition order plus the second analysis frequency multiplied by the second transposition order.

9 . The system according to claim 8 , wherein
the first analysis frequency is ω; the second analysis frequency is (ω+Ω) the first transposition order is (T−r); the second transposition order is r; T>1; and 1≤r<T; such that the synthesis frequency is (T−r)·ω+r·(ω+Ω).

10 . The system according to claim 1 , wherein the analysis filter bank exhibits a frequency spacing which is associated with the fundamental frequency Ω of the audio signal.

11 . A method for decoding an audio signal, the method comprising:
decoding a low frequency component of the audio signal; providing a plurality of analysis subband signals of the low frequency component of the audio signal; receiving information associated with a fundamental frequency Ω of the audio signal; selecting, in response to the information, a first analysis subband signal and a second analysis subband signal from the plurality of analysis subband signals; generating a synthesis subband signal from the first analysis subband signal and the second analysis subband signal, wherein a magnitude of the synthesis subband signal is based on a gain adjusted mean value of magnitudes of the first and second analysis subband signals, and a phase of the synthesis subband signal is based on a weighted sum of phases of the first and second analysis subband signals, wherein weighting factors applied to the phases of the first and second analysis subband signals are integers; and generating a high frequency component of the audio signal from the synthesis subband signal; wherein the information associated with the fundamental frequency Ω of the audio signal is received in an encoded bit stream.

12 . A non-transitory storage medium comprising a software program adapted for execution on a processor and for performing the method step of claim 11 when carried out on a computing device.

Assignees

• Dolby Int Ab

Inventors

• Villemoes Lars
• Hedelin Per

Classifications

• G10L21/0388 Primary

  Details of processing therefor · CPC title

• G10L25/90

  Pitch determination of speech signals · CPC title

• G10L19/02

  using spectral analysis, e.g. transform vocoders or subband vocoders · CPC title

• G10L19/265 Primary

  Pre-filtering, e.g. high frequency emphasis prior to encoding · CPC title

• G10L21/02 Primary

  Speech enhancement, e.g. noise reduction or echo cancellation (reducing echo effects in line transmission systems H04B3/20; echo suppression in hands-free telephones H04M9/08) · CPC title