Multi-Resolution Switched Audio Encoding/Decoding Scheme

• US 20130096930A1
• Filed: 12/06/2012
• Published: 04/18/2013
• Est. Priority Date: 10/08/2008
• Status: Active Grant

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V., VoiceAge Corporation
• Original Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V., VoiceAge Corporation
• Inventors: NEUENDORF, Max, BAYER, Stefan, LECOMTE, Jeremie, FUCHS, Guillaume, ROBILLIARD, Julien, RETTELBACH, Nikolaus, NAGEL, Frederik, MULTRUS, Markus, GRILL, Bernhard, GOURNAY, Philippe, SALAMI, Redwan, GEIGER, Ralf
• Granted Patent: US 9,043,215 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 19/008 Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing
• CPC Class Codes: G10L 19/0212 using orthogonal transformation
• CPC Class Codes: G10L 19/173 Transcoding, i.e. converting between two coded representations avoiding cascaded coding-decoding
• CPC Class Codes: G10L 19/18 Vocoders using multiple modes
• CPC Class Codes: G10L 2019/0008 Algebraic codebooks

Abstract

An audio encoder for encoding an audio signal has a first coding branch, the first coding branch comprising a first converter for converting a signal from a time domain into a frequency domain. Furthermore, the audio encoder has a second coding branch comprising a second time/frequency converter. Additionally, a signal analyzer for analyzing the audio signal is provided. The signal analyzer, on the hand, determines whether an audio portion is effective in the encoder output signal as a first encoded signal from the first encoding branch or as a second encoded signal from a second encoding branch. On the other hand, the signal analyzer determines a time/frequency resolution to be applied by the converters when generating the encoded signals. An output interface includes, in addition to the first encoded signal and the second encoded signal, a resolution information identifying the resolution used by the first time/frequency converter and used by the second time/frequency converter.

Claims

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

a first coding branch for encoding an audio signal using a first coding algorithm to acquire a first encoded signal, the first coding branch comprising the first converter for converting an input signal into a spectral domain;

a second coding branch for encoding an audio signal using a second coding algorithm to acquire a second encoded signal, wherein the first coding algorithm is different from the second coding algorithm, the second coding branch comprising a domain converter for converting an input signal from an input domain into an output domain, and a second converter for converting an input signal into a spectral domain;

a switch for switching between the first coding branch and the second coding branch so that, for a portion of the audio input signal, either the first encoded signal or the second encoded signal is in an encoder output signal;

a signal analyzer for analyzing the portion of the audio signal to determine, whether the portion of the audio signal is represented as the first encoded signal or the second encoded signal in the encoder output signal, wherein the signal analyzer is furthermore configured for variably determining a respective time/frequency resolution of the first converter and the second converter, when the first encoded signal or the second encoded signal representing the portion of the audio signal is generated; and

an output interface for generating an encoder output signal comprising the first encoded signal and the second encoded signal and an information indicating the first encoded signal and the second encoded signal, and an information indicating the time/frequency resolution applied for encoding the first encoded signal and for encoding the second encoded signal.

2. Audio encoder in accordance with claim 1, in which the signal analyzer is configured for classifying the portion of the audio signal as a speech-like audio signal or a music-like audio signal and for performing a transient detection in case of a music signal for determining the time/frequency resolution of the first converter or for performing an analysis-by-synthesis processing for determining the time/frequency resolution of the second converter.

3. Audio encoder in accordance with claim 1, in which the first converter and the second converter comprise a variable windowed transform processor comprising a window function with a variable window size and a transform function with a variable transform length, and

wherein the signal analyzer is configured for controlling, based on the signal analysis, the window size and/or the transform length.

4. Audio encoder in accordance with claim 1, in which the second encoder branch comprises a first processing branch for processing an audio signal in the domain determined by the domain converter, and a second processing branch comprising the second converter,

wherein the signal analyzer is configured for sub-dividing the portion of the audio signal into a sequence of sub-portions, and wherein the signal analyzer is configured for determining the time/frequency resolution of the second converter depending on the position of the sub-portion processed by the first processing branch with respect to a sub-portion of the portion processed by the second processing branch.

5. Audio encoder in accordance with claim 4, in which the first processing branch comprises an ACELP encoder,

in which the second processing branch comprises an MDCT-TCX processing device,

in which the signal analyzer is configured for setting the time resolution of the second converter to a high value determined by a length of a sub-portion or a comparatively lower value determined by a length of the sub-portion multiplied by an integer value greater than one.

6. Audio encoder in accordance with claim 1, in which the signal analyzer is configured for determining a signal classification in a constant raster covering a plurality of equally sized blocks of audio samples, and for sub-dividing a block into a variable number of blocks depending on the audio signal, wherein a length of the sub-block determines the first time/frequency resolution or the second time/frequency resolution.

7. Audio encoder in accordance with claim 1, in which the second coding branch comprises:

a first processing branch for processing an audio signal;

a second processing branch, the second processing branch comprising the second converter; and

a further switch for switching between the first processing branch and the second processing branch so that, for a portion of the audio signal input into the second coding branch, either a first processed signal or a second processed signal is in the second encoded signal.

8. Method of audio encoding an audio signal, comprising:

encoding, in a first coding branch, an audio signal using a first coding algorithm to acquire a first encoded signal, the first coding branch comprising the first converter for converting an input signal into a spectral domain;

encoding, in a second coding branch, an audio signal using a second coding algorithm to acquire a second encoded signal, wherein the first coding algorithm is different from the second coding algorithm, the second coding branch comprising a domain converter for converting an input signal from an input domain into an output domain, and a second converter for converting an input signal into a spectral domain;

switching between the first coding branch and the second coding branch so that, for a portion of the audio input signal, either the first encoded signal or the second encoded signal is in an encoder output signal;

analyzing the portion of the audio signal to determine, whether the portion of the audio signal is represented as the first encoded signal or the second encoded signal in the encoder output signal,

variably determining a respective time/frequency resolution of the first converter and the second converter, when the first encoded signal or the second encoded signal representing the portion of the audio signal is generated; and

generating an encoder output signal comprising the first encoded signal and the second encoded signal and an information indicating the first encoded signal and the second encoded signal, and an information indicating the time/frequency resolution applied for encoding the first encoded signal and for encoding the second encoded signal.

9. Audio decoder for decoding an encoded signal, the encoded signal comprising a first encoded signal, a second encoded signal, an indication indicating the first encoded signal and the second encoded signal, and a time/frequency resolution information to be used for decoding the first encoded signal and the second encoded audio signal, comprising:

a first decoding branch for decoding the first encoded signal using a first controllable frequency/time converter, the first controllable frequency/time converter being configured for being controlled using the time/frequency resolution information for the first encoded signal to acquire a first decoded signal;

a second decoding branch for decoding the second encoded signal using a second controllable frequency/time converter, the second controllable frequency/time converter being configured for being controlled using the time/frequency resolution information for the second encoded signal;

a controller for controlling the first frequency/time converter and the second frequency/time converter using the time/frequency resolution information;

a domain converter for generating a synthesis signal using the second decoded signal; and

a combiner for combining the first decoded signal and the synthesis signal to acquire a decoded audio signal.

10. Audio decoder in accordance with claim 9, in which the second decoding branch comprises a first inverse processing branch for inverse processing a first processed signal being additionally comprised in the encoded signal to acquire a first inverse processed signal;

wherein the second controllable frequency/time converter is located in a second inverse processing branch configured for inverse processing the second encoded signal in a domain identical to the domain of the first inverse processed signal to acquire a second inverse processed signal;

a further combiner for combining the first inverse processed signal and the second inverse processed signal to acquire a combined signal; and

wherein the combined signal is input into the combiner.

11. Audio decoder in accordance with claim 9, in which the first frequency/time converter and the second frequency/time converter are time domain aliasing cancellation converters comprising an overlap/add unit for canceling a time-domain aliasing comprised in the first encoded signal and the second encoded signal.

12. Audio decoder in accordance with claim 9, in which the encoded signal comprises coding mode information identifying, whether an encoded signal is the first encoded signal and the second encoded signal, and

wherein the decoder further comprises an input interface for interpreting the coding mode information to determine, whether the encoded signal is to be fed either into the first decoding branch or into the second decoding branch.

13. Audio decoder in accordance with claim 9, in which the first encoded signal is arithmetically encoded, and wherein the first coding branch comprises an arithmetic decoder.

14. Audio decoder in accordance with claim 9, in which the first coding branch comprises a dequantizer comprising a non-uniform dequantization characteristic for canceling a result of a non-uniform quantization applied when generating the first encoded signal,

wherein the second coding branch comprises a dequantizer using the different dequantization characteristic, where the second coding branch does not comprise a dequantizer.

15. Audio decoder in accordance with claim 9, in which the controller is configured for controlling the first frequency/time converter and the second frequency/time converter by applying, for each converter, a discrete frequency/time resolution of a number of possible different discrete frequency/time resolutions, the number of possible different frequency/time resolutions being higher for the second converter compared to the number of possible different frequency/time resolutions for the first converter.

16. Audio decoder in accordance with claim 9, in which the domain converter is an LPC synthesis processor generating the synthesis signal using a PC filter information, the LPC filter information being comprised in the encoded signal.

17. Method of audio decoding an encoded signal, the encoded signal comprising a first encoded signal, a second encoded signal, an indication indicating the first encoded signal and the second encoded signal, and a time/frequency resolution information to be used for decoding the first encoded signal and the second encoded audio signal, comprising:

decoding, by a first decoding branch, the first encoded signal using a first controllable frequency/time converter, the first controllable frequency/time converter being configured for being controlled using the time/frequency resolution information for the first encoded signal to acquire a first decoded signal;

decoding, by a second decoding branch, the second encoded signal using a second controllable frequency/time converter, the second controllable frequency/time converter being configured for being controlled using the time/frequency resolution information for the second encoded signal;

controlling the first frequency/time converter and the second frequency/time converter using the time/frequency resolution information;

generating, by a domain converter, a synthesis signal using the second decoded signal; and

combining the first decoded signal and the synthesis signal to acquire a decoded audio signal.

18. Encoded audio signal comprising:

a first encoded signal;

a second encoded signal, wherein a portion of an audio signal is either represented by the first encoded signal or the second encoded signal;

an indication indicating the first encoded signal and the second encoded signal;

an indication of a first time/frequency resolution information to be used for decoding the first encoded signal, and

an indication of a second time/frequency resolution information to be used for decoding the second encoded signal.

19. Computer program for performing, when running on a processor, a method of audio encoding an audio signal, comprising:

encoding, in a first coding branch, an audio signal using a first coding algorithm to acquire a first encoded signal, the first coding branch comprising the first converter for converting an input signal into a spectral domain;

encoding, in a second coding branch, an audio signal using a second coding algorithm to acquire a second encoded signal, wherein the first coding algorithm is different from the second coding algorithm, the second coding branch comprising a domain converter for converting an input signal from an input domain into an output domain, and a second converter for converting an input signal into a spectral domain;

switching between the first coding branch and the second coding branch so that, for a portion of the audio input signal, either the first encoded signal or the second encoded signal is in an encoder output signal;

analyzing the portion of the audio signal to determine, whether the portion of the audio signal is represented as the first encoded signal or the second encoded signal in the encoder output signal,

variably determining a respective time/frequency resolution of the first converter and the second converter, when the first encoded signal or the second encoded signal representing the portion of the audio signal is generated; and

generating an encoder output signal comprising the first encoded signal and the second encoded signal and an information indicating the first encoded signal and the second encoded signal, and an information indicating the time/frequency resolution applied for encoding the first encoded signal and for encoding the second encoded signal

or

the method of audio decoding an encoded signal, the encoded signal comprising a first encoded signal, a second encoded signal, an indication indicating the first encoded signal and the second encoded signal, and a time/frequency resolution information to be used for decoding the first encoded signal and the second encoded audio signal, comprising;

decoding, by a first decoding branch, the first encoded signal using a first controllable frequency/time converter, the first controllable frequency/time converter being configured for being controlled using the time/frequency resolution information for the first encoded signal to acquire a first decoded signal;

decoding, by a second decoding branch, the second encoded signal using a second controllable frequency/time converter, the second controllable frequency/time converter being configured for being controlled using the time/frequency resolution information for the second encoded signal;

controlling the first frequency/time converter and the second frequency/time converter using the time/frequency resolution information;

generating, by a domain converter, a synthesis signal using the second decoded signal; and

combining the first decoded signal and the synthesis signal to acquire a decoded audio signal.