High frequency regeneration of an audio signal with synthetic sinusoid addition

• US 9,761,236 B2
• Filed: 03/08/2017
• Issued: 09/12/2017
• 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:
  US15/452,948
• Publication Number:
  US 20170178657A1
• Time in Patent Office: 188 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

A method performed in an audio decoder for reconstructing an original audio signal having a lowband portion and a highband portion is disclosed. The method includes receiving an encoded audio signal and extracting reconstruction parameters from the encoded audio signal. The method further includes decoding the encoded audio signal with a core audio decoder to obtain a decoded lowband portion and regenerating the highband portion based at least in part on a cross over frequency and the decoded lowband portion to obtain a regenerated highband portion. The method also includes creating a synthetic sinusoid with a level based at least in part on a spectral envelope value for the particular subband and a noise floor value for the particular subband and adding the synthetic sinusoid to the regenerated highband portion in the particular frequency band specified by the location information. Finally, the method includes combining the lowband portion and the regenerated highband portion to obtain a full bandwidth audio signal.

Claims

1. An audio decoder for decoding an encoded audio bitstream, the audio decoder comprising:

a demultiplexer for extracting a frequency domain representation of a lowband audio signal having frequency content below a predetermined frequency, envelope data, and additional information from the encoded audio bitstream;

a core decoder for receiving the frequency domain representation of the lowband audio signal and decoding the frequency domain representation of the lowband audio signal to produce a time domain lowband audio signal;

an envelope decoder for receiving the envelope data and decoding the envelope data to produce an estimated spectral envelope;

an analysis filterbank for filtering the time domain lowband audio signal to produce a subband domain representation of the lowband audio signal;

a high frequency reconstructor for regenerating a subband domain representation of a highband audio signal from the subband domain representation of the lowband audio signal;

a manipulator for adding a spectral line that is a sinusoidal component specified by the additional information to the subband domain representation of the highband audio signal;

an envelope adjuster for adjusting a spectral envelope of the subband domain representation of the highband audio signal based, at least in part, on the estimated spectral envelope; and

a synthesis filterbank for combining the subband domain representation of the lowband audio signal and the subband domain representation of the highband audio signal to produce a wideband time domain audio signal, and output the produced wideband time domain audio signal;

wherein the high frequency reconstructor includes a transposer for transposing several consecutive analysis filter bank channels below the predetermined frequency to certain consecutive synthesis filter bank channels above the predetermined frequency,

wherein the analysis filterbank and the synthesis filterbank are complex quadrature mirror filter (QMF) banks,

wherein the predetermined frequency includes a variable cross-over frequency, wherein the core decoder operates at half the sampling rate of the high frequency reconstructor, and

wherein one or more of the demultiplexer, the core decoder, the envelope decoder, the analysis filterbank, the high frequency reconstructor, the manipulator, the envelope adjuster, and the synthesis filterbank are implemented, at least in part, by one or more hardware elements of the audio decoder.

2. The audio decoder of claim 1, wherein the manipulator comprises a parametric decoder of the spectral line or a waveform decoder of the spectral line.

3. The audio decoder of claim 1 wherein the high frequency reconstructor operates at 44.1 kHz.

4. A method for decoding an encoded audio bitstream, the method comprising:

extracting a frequency domain representation of a lowband audio signal having frequency content below a predetermined frequency, envelope data, and additional information from the encoded audio bitstream;

receiving the frequency domain representation of the lowband audio signal and decoding the frequency domain representation of the lowband audio signal to produce a time domain lowband audio signal;

receiving the envelope data and decoding the envelope data to produce an estimated spectral envelope;

filtering the time domain lowband audio signal to produce a subband domain representation of the lowband audio signal;

regenerating a subband domain representation of a highband audio signal from the subband domain representation of the lowband audio signal;

adding a spectral line that is a sinusoidal component specified by the additional information to the subband domain representation of the highband audio signal;

adjusting a spectral envelope of the subband domain representation of the highband audio signal based, at least in part, on the estimated spectral envelope; and

combining the subband domain representation of the lowband audio signal and the subband domain representation of the highband audio signal to produce a wideband time domain audio signal, the produced wideband time domain audio signal is output as a wideband signal,

wherein the regenerating includes transposing several consecutive analysis filter bank channels below the predetermined frequency to certain consecutive synthesis filter bank channels above the predetermined frequency,

wherein the filtering and the combining are implemented with complex quadrature mirror filter (QMF) banks,

wherein the predetermined frequency includes a variable cross-over frequency,

wherein the decoding the frequency domain representation of the lowband audio signal operates at half the sampling rate of the regenerating, and

wherein the method is performed, at least in part, with one or more hardware elements.

5. A non-transitory computer readable medium containing instructions that when executed by a processor perform the method of claim 4.