Apparatus and method for encoding and decoding an encoded audio signal using temporal noise/patch shaping

• US 10,347,274 B2
• Filed: 02/13/2017
• Issued: 07/09/2019
• Est. Priority Date: 07/22/2013
• 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: Disch, Sascha, Nagel, Frederik, Geiger, Ralf, Thoshkahna, Balaji Nagendran, Schmidt, Konstantin, Bayer, Stefan, Neukam, Christian, Edler, Bernd, Helmrich, Christian
• Primary Examiner(s): Opsasnick, Michael N
• Application Number:
  US15/431,571
• Publication Number:
  US 20170154631A1
• Time in Patent Office: 876 Days
• Field of Search: 704207, 704500-504
• CPC Class Codes: G10L 19/008 Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing
• CPC Class Codes: G10L 19/02 using spectral analysis, e.g. transform vocoders or subband vocoders
• CPC Class Codes: G10L 19/0204 using subband decomposition
• CPC Class Codes: G10L 19/0208 Subband vocoders
• CPC Class Codes: G10L 19/0212 using orthogonal transformation
• CPC Class Codes: G10L 19/022 Blocking, i.e. grouping of samples in time; Choice of analysis windows; Overlap factoring
• CPC Class Codes: G10L 19/025 Detection of transients or attacks for time/frequency resolution switching
• CPC Class Codes: G10L 19/03 Spectral prediction for preventing pre-echo; Temporary noise shaping [TNS], e.g. in MPEG2 or MPEG4
• CPC Class Codes: G10L 19/032 Quantisation or dequantisation of spectral components
• 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 21/0388 Details of processing therefor
• CPC Class Codes: G10L 25/06 the extracted parameters being correlation coefficients
• CPC Class Codes: G10L 25/18 the extracted parameters being spectral information of each sub-band
• CPC Class Codes: G10L 25/21 the extracted parameters being power information
• CPC Class Codes: H04S 1/007 in which the audio signals are in digital form data reduction aspects thereof based on psychoacoustics G10L19/02

Abstract

An apparatus for decoding an encoded audio signal, includes: a spectral domain audio decoder for generating a first decoded representation of a first set of first spectral portions being spectral prediction residual values; a frequency regenerator for generating a reconstructed second spectral portion using a first spectral portion of the first set of first spectral portions, wherein the reconstructed second spectral portion additionally includes spectral prediction residual values; and an inverse prediction filter for performing an inverse prediction over frequency using the spectral residual values for the first set of first spectral portions and the reconstructed second spectral portion using prediction filter information included in the encoded audio signal.

Claims

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

a time-spectrum converter configured for converting the audio signal into a spectral representation having spectral values in a spectral transform domain;

a prediction filter configured for performing a prediction over frequency on the spectral representation having the spectral values in the spectral transform domain to generate spectral residual values, the prediction filter being defined by filter information derived from the audio signal, wherein the prediction filter is configured to calculate a set of prediction coefficients from the spectral values in the spectral transform domain using the prediction over frequency in the spectral transform domain, and to calculate the spectral residual values corresponding to the set of prediction coefficients, the spectral residual values having a flatter temporal spectrum compared to the spectral values in the spectral transform domain, the filter information being based on the set of prediction coefficients;

an audio coder configured for encoding a first set of first spectral portions of the spectral residual values to acquire an encoded first set of first spectral values comprising a first spectral resolution;

a parametric coder configured for parametrically encoding a second set of second spectral portions of the spectral residual values or of the spectral values of the spectral representation in the spectral transform domain to acquire an encoded second set of second spectral values comprising a second spectral resolution being lower than the first spectral resolution; and

an output interface configured for outputting the encoded audio signal comprising the encoded second set of second spectral values, the encoded first set of first spectral values, and the filter information,

wherein one or more of the time-spectrum converter, the prediction filter, the audio coder, the parametric coder, and the output interface is implemented, at least in part, by one or more hardware elements of the audio encoder.

2. Audio encoder of claim 1,

wherein the time-spectrum converter is configured for performing a modified discrete cosine transform, and wherein the spectral residual values are modified discrete cosine transform spectral residual values.

3. Audio encoder of claim 1,

wherein the prediction filter comprises a filter information calculator, the filter information calculator being configured for using spectral values of a spectral representation to calculate the filter information and wherein the prediction filter is configured for calculating the spectral residual values using spectral values of the spectral representation, wherein the spectral values for calculating the filter information and the spectral values input into the prediction filter are derived from the same audio signal.

4. Audio encoder of claim 1,

wherein the prediction filter comprises a filter calculator configured for calculating the filter information using spectral values from a TNS start frequency to a TNS stop frequency, wherein the TNS start frequency is lower than 4 kHz and the TNS stop frequency is greater than 9 kHz.

5. Audio encoder of claim 1, further comprising an analyzer configured for determining the first set of the first spectral portions to be encoded by the audio encoder, the analyzer using a gap filling start frequency, wherein spectral portions below the gap filling start frequency are the first spectral portions of the first set of the first spectral portions, and

wherein the TNS stop frequency is greater than the gap filling start frequency.

6. Audio encoder of claim 1,

wherein the time-frequency converter is configured for providing a complex spectral representation,

wherein the prediction filter is configured for performing a prediction over frequency with the complex-valued spectral representation, and

wherein the filter information is configured to define a complex inverse prediction filter.

7. Method of encoding an audio signal to obtain an encoded audio signal, comprising:

converting the audio signal into a spectral representation having spectral values in a spectral transform domain;

performing a prediction over frequency on the spectral representation having the spectral values in the spectral transform domain to generate spectral residual values, the prediction filter being defined by filter information derived from the audio signal, wherein the performing the prediction over frequency comprises calculating a set of prediction coefficients from the spectral values in the spectral transform domain using the prediction over frequency in the spectral transform domain, and calculating the spectral residual values corresponding to the set of prediction coefficients, the spectral residual values having a flatter temporal spectrum compared to the spectral values in the spectral transform domain, the filter information being based on the set of prediction coefficients;

encoding a first set of first spectral portions of the spectral residual values to acquire an encoded first set of first spectral values comprising a first spectral resolution;

parametrically encoding a second set of second spectral portions of the spectral residual values or of the spectral values of the spectral representation in the spectral transform domain to acquire an encoded second set of second spectral values comprising a second spectral resolution being lower than the first spectral resolution; and

outputting the encoded audio signal comprising the encoded second set of second spectral values, the encoded first set of first spectral values, and the filter information,

wherein one or more of the converting, the performing the prediction, the encoding, the parametrically encoding, and the outputting is implemented, at least in part, by one or more hardware elements of an audio signal processing device.

8. A non-transitory storage medium having stored thereon a computer program for performing, when running on a computer or a processor, a method of encoding an audio signal to obtain an encoded audio signal, the method comprising:

converting the audio signal into a spectral representation having spectral values in a spectral transform domain;

performing a prediction over frequency on the spectral representation having the spectral values in the spectral transform domain to generate spectral residual values, the prediction filter being defined by filter information derived from the audio signal, wherein the performing the prediction over frequency comprises calculating a set of prediction coefficients from the spectral values in the spectral transform domain using the prediction over frequency in the spectral transform domain, and calculating the spectral residual values corresponding to the set of prediction coefficients, the spectral residual values having a flatter temporal spectrum compared to the spectral values in the spectral transform domain, the filter information being based on the set of prediction coefficients;

encoding a first set of first spectral portions of the spectral residual values to acquire an encoded first set of first spectral values comprising a first spectral resolution;

parametrically encoding a second set of second spectral portions of the spectral residual values or of the spectral values of the spectral representation in the spectral transform domain to acquire an encoded second set of second spectral values comprising a second spectral resolution being lower than the first spectral resolution; and

outputting the encoded audio signal comprising the encoded second set of second spectral values, the encoded first set of first spectral values, and the filter information.