Low bitrate audio encoding/decoding scheme having cascaded switches

• US 8,930,198 B2
• Filed: 01/11/2011
• Issued: 01/06/2015
• Est. Priority Date: 07/11/2008
• 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: Grill, Bernhard, Lefebvre, Roch, Bessette, Bruno, Lapierre, Jimmy, Gournay, Philippe, Salami, Redwan, Bayer, Stefan, Fuchs, Guillaume, Geyersberger, Stefan, Geiger, Ralf, Hilpert, Johannes, Kraemer, Ulrich, Lecomte, Jeremie, Multrus, Markus, Neuendorf, Max, Popp, Harald, Rettelbach, Nikolaus
• Primary Examiner(s): Lerner, Martin
• Application Number:
  US13/004,385
• Publication Number:
  US 20110202354A1
• Time in Patent Office: 1,456 Days
• Field of Search: 704/205, 704/206, 704/219, 704/220, 704/221, 704/500, 704/501, 704/203
• 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 has a first information sink oriented encoding branch, a second information source or SNR oriented encoding branch, and a switch for switching between the first encoding branch and the second encoding branch, wherein the second encoding branch has a converter into a specific domain different from the spectral domain, and wherein the second encoding branch furthermore has a specific domain coding branch, and a specific spectral domain coding branch, and an additional switch for switching between the specific domain coding branch and the specific spectral domain coding branch. An audio decoder has a first domain decoder, a second domain decoder for decoding a signal, and a third domain decoder and two cascaded switches for switching between the decoders.

Claims

1. Audio encoding apparatus for encoding an audio input signal, the audio input signal being in a first domain, comprising:

a first coding branch for encoding an audio signal using a first coding algorithm to acquire a first encoded signal;

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; and

a first 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,

wherein the second coding branch comprises;

a converter for converting the audio signal into a second domain different from the first domain,

a first processing branch for processing an audio signal in the second domain to acquire a first processed signal;

a second processing branch for converting a signal into a third domain different from the first domain and the second domain and for processing the signal in the third domain to acquire a second processed signal; and

a second 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 the first processed signal or the second processed signal is in the second encoded signal,

wherein the first coding branch and the second coding branch are operative to encode the audio signal in a block wise manner, wherein the first switch or the second switch are switching in a block-wise manner so that a switching action takes place, at the minimum, after a block of a predefined number of samples of a signal, the predefined number of samples forming a frame length for the corresponding switch,

wherein the frame length for the first switch is at least double the size of the frame length of the second switch, and

wherein at least one of the first coding branch, the second coding branch, the first switch, the first converter, the first processing branch, the second processing branch, and the second switch comprises a hardware implementation.

2. Audio encoding apparatus in accordance with claim 1, in which the first coding algorithm in the first coding branch is based on an information sink model, or in which the second coding algorithm in the second coding branch is based on an information source or a signal to noise ratio model.

3. Audio encoding apparatus in accordance with claim 1, in which the first coding branch comprises a converter for converting the audio input signal into a fourth domain different from the first domain, the second domain, and the third domain.

4. Audio encoding apparatus in accordance with claim 1, in which the first domain is the time domain, the second domain is an LPC domain acquired by an LPC filtering the first domain signal, the third domain is an LPC spectral domain acquired by converting an LPC filtered signal into a spectral domain, and the fourth domain is a spectral domain acquired by frequency domain converting the first domain signal.

5. Audio encoding apparatus in accordance with claim 1, further comprising a controller for controlling the first switch or the second switch in a signal adaptive way,

wherein the controller is operative to analyze a signal input into the first switch or output by the first coding branch or the second coding branch or a signal acquired by decoding an output signal of the first coding branch or the second coding branch with respect to a target function, or

wherein the controller is operative to analyze a signal input into the second switch or output by the first processing branch or the second processing branch or signals acquired by inverse processing output signals from the first processing branch and the second processing branch with respect to a target function.

6. Audio encoding apparatus in accordance with claim 5, in which the controller is operative to control the first switch in an open loop manner and to control the second switch in a closed loop manner.

7. Audio encoding apparatus in accordance with claim 1, in which the first coding branch or the second processing branch of the second coding branch comprises an aliasing introducing time/frequency converter and a quantizer/entropy coder stage and wherein the first processing branch of the second coding branch comprises a quantizer or entropy coder stage without an aliasing introducing conversion.

8. Audio encoding apparatus in accordance with claim 7, in which the aliasing introducing time/frequency converter comprises a windower for applying an analysis window and a modified discrete cosine transform algorithm, the windower being operative to apply the window function to subsequent frames in an overlapping manner so that a sample of an input signal into the windower occurs in at least two subsequent frames.

9. Audio encoding apparatus in accordance with claim 1, in which the first processing branch comprises the LPC excitation coding of an algebraic code excited linear prediction coder and the second processing branch comprises an MDCT spectral converter and a quantizer for quantizing spectral components to acquire quantized spectral components, wherein each quantized spectral component is zero or is defined by one quantization index of a plurality of quantization indices.

10. Audio encoding apparatus in accordance with claim 1, in which the first encoding branch or the second processing branch of the second coding branch comprises a variable time warping functionality.

11. Method of encoding an audio input signal, the audio input signal being in a first domain, comprising:

encoding, by a first coding branch, an audio signal using a first coding algorithm to acquire a first encoded signal;

encoding, by 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; and

switching, by a first switch, between encoding using the first coding algorithm and encoding using the second coding algorithm so that, for a portion of the audio input signal, either the first encoded signal or the second encoded signal is in an encoded output signal,

wherein encoding using the second coding algorithm comprises;

converting, by a converter, the audio signal into a second domain different from the first domain,

processing, by a first processing branch, an audio signal in the second domain to acquire a first processed signal;

converting, by a second processing branch, a signal into a third domain different from the first domain and the second domain and processing the signal in the third domain to acquire a second processed signal; and

switching, by a second switch, between processing the audio signal and converting and processing so that, for a portion of the audio signal encoded using the second coding algorithm, either the first processed signal or the second processed signal is in the second encoded signal,

wherein the first coding branch and the second coding branch are operative to encode the audio signal in a block wise manner, wherein the first switch or the second switch are switching in a block-wise manner so that a switching action takes place, at the minimum, after a block of a predefined number of samples of a signal, the predefined number of samples forming a frame length for the corresponding switch,

wherein the frame length for the first switch is at least double the size of the frame length of the second switch, and

wherein at least one of the first coding branch, the second coding branch, the first switch, the first converter, the first processing branch, the second processing branch, and the second switch comprises a hardware implementation.

12. A non-transitory storage medium having stored thereon a computer program for performing, when running on the computer, the method of encoding an audio signal, the audio input signal being in a first domain, comprising:

encoding an audio signal using a first coding algorithm to acquire a first encoded signal;

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; and

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

wherein encoding using the second coding algorithm comprises;

converting the audio signal into a second domain different from the first domain,

processing an audio signal in the second domain to acquire a first processed signal;

converting a signal into a third domain different from the first domain and the second domain and processing the signal in the third domain to acquire a second processed signal; and

switching between processing the audio signal and converting and processing so that, for a portion of the audio signal encoded using the second coding algorithm, either the first processed signal or the second processed signal is in the second encoded signal,

wherein the first coding branch and the second coding branch are operative to encode the audio signal in a block wise manner, wherein the first switch or the second switch are switching in a block-wise manner so that a switching action takes place, at the minimum, after a block of a predefined number of samples of a signal, the predefined number of samples forming a frame length for the corresponding switch, and

wherein the frame length for the first switch is at least double the size of the frame length of the second switch.

13. Audio encoding apparatus for encoding an audio input signal, the audio input signal being in a first domain, comprising:

a first coding branch for encoding an audio signal using a first coding algorithm to acquire a first encoded signal;

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;

a first 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,

wherein the second coding branch comprises;

a converter for converting the audio signal into a second domain different from the first domain,

a first processing branch for processing an audio signal in the second domain to acquire a first processed signal;

a second processing branch for converting a signal into a third domain different from the first domain and the second domain and for processing the signal in the third domain to acquire a second processed signal; and

a second 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 the first processed signal or the second processed signal is in the second encoded signal, and

a controller for controlling the first switch or the second switch in a signal adaptive way,

wherein the controller is operative to analyze a signal input into the first switch or output by the first coding branch or the second coding branch or a signal acquired by decoding an output signal of the first coding branch or the second coding branch with respect to a target function, or

wherein the controller is operative to analyze a signal input into the second switch or output by the first processing branch or the second processing branch or signals acquired by inverse processing output signals from the first processing branch and the second processing branch with respect to a target function,

wherein the controller is operative to perform a speech/music discrimination in such a way that a decision to speech is favored with respect to a decision to music so that a decision to speech is taken even when a portion less than 50% of a frame for the first switch is speech and a portion more than 50% of the frame for the first switch is music, or

wherein a frame for the second switch is smaller than a frame for the first switch, and wherein the controller is operative to take a decision to speech when only a portion of the first frame which comprises a length which is more than 50% of the length of the second frame is found out to comprise music, and

wherein at least one of the first coding branch, the second coding branch, the first switch, the first converter, the first processing branch, the second processing branch, the controller, and the second switch comprises a hardware implementation.

14. Audio encoding apparatus in accordance with claim 13, in which the first coding branch and the second coding branch are operative to encode the audio signal in a block wise manner, wherein the first switch or the second switch are switching in a block-wise manner so that a switching action takes place, at the minimum, after a block of a predefined number of samples of a signal, the predefined number of samples forming a frame length for the corresponding switch.

15. Method of encoding an audio input signal, the audio input signal being in a first domain, comprising:

encoding, by a first coding branch, an audio signal using a first coding algorithm to acquire a first encoded signal;

encoding, by 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;

switching, by a first switch, between encoding using the first coding algorithm and encoding using the second coding algorithm so that, for a portion of the audio input signal, either the first encoded signal or the second encoded signal is in an encoded output signal,

wherein encoding using the second coding algorithm comprises;

converting, by a converter, the audio signal into a second domain different from the first domain,

processing, by a first processing branch, an audio signal in the second domain to acquire a first processed signal;

converting, by a second processing branch, a signal into a third domain different from the first domain and the second domain and processing the signal in the third domain to acquire a second processed signal; and

switching, by a second switch, between processing the audio signal and converting and processing so that, for a portion of the audio signal encoded using the second coding algorithm, either the first processed signal or the second processed signal is in the second encoded signal,

controlling, by a controller, the first switch or the second switch in a signal adaptive way,

wherein the controlling comprises analyzing a signal input into the first switch or output by the first coding branch or the second coding branch or a signal acquired by decoding an output signal of the first coding branch or the second coding branch with respect to a target function, or

wherein the controlling comprises analyzing a signal input into the second switch or output by the first processing branch or the second processing branch or signals acquired by inverse processing output signals from the first processing branch and the second processing branch with respect to a target function,

wherein the controlling comprises performing a speech/music discrimination in such a way that a decision to speech is favored with respect to a decision to music so that a decision to speech is taken even when a portion less than 50% of a frame for the first switch is speech and a portion more than 50% of the frame for the first switch is music, or

wherein a frame for the second switch is smaller than a frame for the first switch, and wherein the controlling comprises taking a decision to speech when only a portion of the first frame which comprises a length which is more than 50% of the length of the second frame is found out to comprise music, and

wherein at least one of the first coding branch, the second coding branch, the first switch, the first converter, the first processing branch, the second processing branch, the controller, and the second switch comprises a hardware implementation.

16. A non-transitory storage medium having stored thereon a computer program for performing, when running on the computer, the method of encoding an audio signal, the audio input signal being in a first domain, comprising:

encoding an audio signal using a first coding algorithm to acquire a first encoded signal;

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; and

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

wherein encoding using the second coding algorithm comprises;

converting the audio signal into a second domain different from the first domain,

processing an audio signal in the second domain to acquire a first processed signal;

converting a signal into a third domain different from the first domain and the second domain and processing the signal in the third domain to acquire a second processed signal; and

switching between processing the audio signal and converting and processing so that, for a portion of the audio signal encoded using the second coding algorithm, either the first processed signal or the second processed signal is in the second encoded signal,

controlling, by a controller, the first switch or the second switch in a signal adaptive way,

wherein the controlling comprises analyzing a signal input into the first switch or output by the first coding branch or the second coding branch or a signal acquired by decoding an output signal of the first coding branch or the second coding branch with respect to a target function, or

wherein the controlling comprises analyzing a signal input into the second switch or output by the first processing branch or the second processing branch or signals acquired by inverse processing output signals from the first processing branch and the second processing branch with respect to a target function,

wherein the controlling comprises performing a speech/music discrimination in such a way that a decision to speech is favored with respect to a decision to music so that a decision to speech is taken even when a portion less than 50% of a frame for the first switch is speech and a portion more than 50% of the frame for the first switch is music, or

wherein a frame for the second switch is smaller than a frame for the first switch, and wherein the controlling comprises taking a decision to speech when only a portion of the first frame which comprises a length which is more than 50% of the length of the second frame is found out to comprise music.