Concept for encoding an audio signal and decoding an audio signal using deterministic and noise like information

• US 10,304,470 B2
• Filed: 04/18/2016
• Issued: 05/28/2019
• Est. Priority Date: 10/18/2013
• 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: Fuchs, Guillaume, Multrus, Markus, Ravelli, Emmanuel, Schnell, Markus
• Primary Examiner(s): Neway, Samuel G
• Application Number:
  US15/131,773
• Publication Number:
  US 20160232908A1
• Time in Patent Office: 1,135 Days
• 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 19/08 Determination or coding of the excitation function; Determination or coding of the long-term prediction parameters
• CPC Class Codes: G10L 19/083 the excitation function being an excitation gain G10L25/90 takes precedence
• CPC Class Codes: G10L 19/12 the excitation function being a code excitation, e.g. in code excited linear prediction [CELP] vocoders
• CPC Class Codes: G10L 19/20 using sound class specific coding, hybrid encoders or object based coding
• CPC Class Codes: G10L 2019/0016 Codebook for LPC parameters
• CPC Class Codes: G10L 2025/932 Decision in previous or following frames
• CPC Class Codes: G10L 25/15 the extracted parameters being formant information

Abstract

An encoder for encoding an audio signal has: an analyzer configured for deriving prediction coefficients and a residual signal from an unvoiced frame of the audio signal; a gain parameter calculator configured for calculating a first gain parameter information for defining a first excitation signal related to a deterministic codebook and for calculating a second gain parameter information for defining a second excitation signal related to a noise-like signal for the unvoiced frame; and a bitstream former configured for forming an output signal based on an information related to a voiced signal frame, the first gain parameter information and the second gain parameter information.

Claims

1. An encoder for encoding an audio signal, the encoder comprising:

an analyzer configured for deriving prediction coefficients and a residual signal from a frame of the audio signal;

a decider configured for determining if the residual signal was determined from an unvoiced frame;

a gain parameter calculator configured for calculating a first gain parameter information for defining a first excitation signal related to a deterministic codebook and for calculating a second gain parameter information for defining a second excitation signal related to a noise-like signal for the unvoiced frame;

a bitstream former configured for forming an output signal based on an information related to a voiced signal frame, the first gain parameter information and the second gain parameter information; and

wherein the encoder comprises an LTP (Long-Term Prediction) memory and a signal generator for generating an adaptive excitation signal that is set to zero for the unvoiced frame;

wherein, when compared to a CELP coding scheme, the encoder is configured for not transmitting LTP parameters for the unvoiced frame to save bits, wherein the deterministic codebook is configured to code more pulses for a same bit-rate using the saved bits; and

wherein one or more of the analyzer, the gain parameter calculator, the bitstream former and the decider is implemented, at least in part, by one or more hardware elements of the apparatus.

2. The encoder according to claim 1, wherein the gain parameter calculator is configured for calculating a first gain parameter and a second gain parameter and wherein the bitstream former is configured for forming the output signal based on the first gain parameter and the second gain parameter;

or

wherein the gain parameter calculator comprises a quantizer configured for quantizing the first gain parameter for acquiring a first quantized gain parameter and for quantizing the second gain parameter for acquiring a second quantized gain parameter and wherein the bitstream former is configured for forming the output signal based on the first quantized gain parameter and the second quantized gain parameter.

3. The encoder according to claim 1, further comprising a formant information calculator configured for calculating a speech related spectral shaping information from the prediction coefficients and wherein the gain parameter calculator is configured to calculate the first gain parameter information and the second gain parameter information based on the speech related spectral shaping information.

4. The encoder according to claim 1, wherein the second excitation signal is different when compared to the first excitation signal, wherein the gain parameter calculator comprises:

a first amplifier configured for amplifying the first excitation signal by applying the first gain parameter to acquire a first amplified excitation signal;

a second amplifier configured for amplifying the second excitation signal different from the first excitation signal by applying the second gain parameter to acquire a second amplified excitation signal;

a combiner configured for combining the first amplified excitation signal and the second amplified excitation signal to acquire a combined excitation signal;

a controller configured for filtering the combined excitation signal with a synthesis filter to acquire a synthesized signal, for comparing the synthesized signal and the audio signal frame to acquire a comparison result, to adapt the first gain parameter or the second gain parameter based on the comparison result; and

wherein the bitstream former is configured for forming the output signal based on an information related to the first gain parameter and the second gain parameter.

5. The encoder according to claim 1, wherein the gain parameter calculator further comprises at least one shaper configured for spectrally shaping the first excitation signal or a signal derived thereof or the second excitation signal or a signal derived thereof based on a spectral shaping information.

6. The encoder according to claim 1, wherein the encoder is configured for encoding the audio signal framewise in a sequence of frames and wherein the gain parameter calculator is configured for determining the first gain parameter and the second gain parameter for each of a plurality of subframes of a processed frame and wherein the gain parameter controller is configured for determining an average energy value associated to the processed frame.

7. The encoder according to claim 1, further comprising:

a formant information calculator configured for calculating at least a first a speech related spectral shaping information from the prediction coefficients.

8. The encoder according to claim 1, wherein the gain parameter calculator comprises a controller configured for determining the first gain parameter based on:

9. The encoder according to claim 1, further comprising a quantizer configured for quantizing the first gain parameter to acquire a quantized first gain parameter, wherein the gain parameter calculator is configured for determining the first gain parameter as a based on:

10. The encoder according to claim 9, wherein the quantizer is configured for quantizing the second gain parameter to acquire a quantized second gain parameter wherein the gain parameter calculator is configured to determine the second gain parameter by determining an error value based on:

11. The encoder according to claim 10, wherein a combiner is configured for combining the first gain parameter and the second gain parameter to acquire a combines excitation signal based on:

e(n)=ĝ

_c·

c(n)+ĝ

_n·

n(n).

19. The encoder according to claim 10, wherein the quantizer is configured for determining the error value based on an energy mismatch between the first shaped excitation signal and the second excitation signal, wherein the quantizer is configured for determining the first gain parameter based on a mean squared error or mean squared root error.

12. A decoder for decoding a received audio signal comprising an information related to prediction coefficients, the decoder comprising:

a first signal generator configured for generating a first excitation signal from a deterministic codebook for a portion of a synthesized signal;

a second signal generator configured for generating a second excitation signal from a noise-like signal for the portion of the synthesized signal;

a combiner configured for combining the first excitation signal and the second excitation signal for generating a combined excitation signal for the portion of the synthesized signal; and

a synthesizer configured for synthesizing the portion of the synthesized signal from the combined excitation signal and the prediction coefficients;

wherein the received audio signal does not comprise LTP (Long-Term Prediction) parameters for an unvoiced frame, wherein an adaptive excitation signal is set to zero for the unvoiced frame, and wherein more pulses are provided for a same bit-rate due to bits saved because of the lack of LTP parameters for the unvoiced frame; and

wherein one or more of the first signal generator, the second signal generator, the combiner and the synthesizer is implemented, at least in part, by one or more hardware elements of the apparatus.

13. The decoder according to claim 12, wherein the received audio signal comprises an information related to a first gain parameter and to a second gain parameter, wherein the decoder further comprises:

a first amplifier configured for amplifying the first excitation signal or a signal derived thereof by applying the first gain parameter to acquire a first amplified excitation signal;

a second amplifier configured for amplifying the second excitation signal or a signal derived by applying the second gain parameter to acquire a second amplified excitation signal.

14. The decoder according to claim 12, further comprising:

a formant information calculator configured for calculating a first spectral shaping information and a second spectral shaping information from the prediction coefficients;

a first shaper for spectrally shaping a spectrum of the first excitation signal or a signal derived thereof using the first spectral shaping information; and

a second shaper for spectrally shaping a spectrum of the second excitation signal or a signal derived thereof using the second shaping information.

15. A method for encoding an audio signal, the method comprising:

deriving prediction coefficients and a residual signal from a frame of the audio signal;

determining if the residual signal was determined from an unvoiced signal audio frame;

calculating a first gain parameter information for defining a first excitation signal related to a deterministic codebook and for calculating a second gain parameter information for defining a second excitation signal related to a noise-like signal for the unvoiced frame;

forming an output signal based on an information related to a voiced signal frame, the first gain parameter information and the second gain parameter information;

generating an adaptive excitation signal that is set to zero for the unvoiced frame using an LTP (Long-Term Prediction) memory and a signal generator; and

when compared to a CELP coding scheme, not transmitting LTP parameters for the unvoiced frame to save bits and coding more pulses for a same bit-rate using the deterministic codebook and using the saved bits.

16. A method for decoding a received audio signal comprising an information related to prediction coefficients, the decoder comprising:

generating a first excitation signal from a deterministic codebook for a portion of a synthesized signal;

generating a second excitation signal from a noise-like signal for the portion of the synthesized signal;

combining the first excitation signal and the second excitation signal for generating a combined excitation signal for the portion of the synthesized signal;

synthesizing the portion of the synthesized signal from the combined excitation signal and the prediction coefficients;

wherein the received audio signal does not comprise LTP (Long-Term Prediction) parameters for an unvoiced frame, wherein in the received audio signal, an adaptive excitation signal is set to zero for the unvoiced frame, and provides more pulses for a same bit-rate due to bits saved because of the lack of LTP parameters for the unvoiced frame using a deterministic codebook.

17. A non-transitory digital storage medium having stored thereon a computer program for executing a method for encoding an audio signal, the method comprising:

deriving prediction coefficients and a residual signal from a frame of the audio signal;

determining if the residual signal was determined from an unvoiced frame;

calculating a first gain parameter information for defining a first excitation signal related to a deterministic codebook and for calculating a second gain parameter information for defining a second excitation signal related to a noise-like signal for the unvoiced frame;

forming an output signal based on an information related to a voiced signal frame, the first gain parameter information and the second gain parameter information;

generating an adaptive excitation signal that is set to zero for the unvoiced frame using an LTP (Long-Term Prediction) memory and a signal generator; and

when compared to a CELP coding scheme, not transmitting LTP parameters for the unvoiced frame to save bits and coding more pulses for a same bit-rate using the deterministic codebook and using the saved bits,

when running on a computer.

18. A non-transitory digital storage medium having stored thereon a computer program for executing a method for decoding a received audio signal comprising an information related to prediction coefficients, the method comprising:

generating a first excitation signal from a deterministic codebook for a portion of a synthesized signal;

generating a second excitation signal from a noise-like signal for the portion of the synthesized signal;

combining the first excitation signal and the second excitation signal for generating a combined excitation signal for the portion of the synthesized signal; and

synthesizing the portion of the synthesized signal from the combined excitation signal and the prediction coefficients;

wherein the received audio signal does not comprise LTP (Long-Term Prediction) parameters for an unvoiced frame, wherein in the received audio signal, an adaptive excitation signal is set to zero for an unvoiced frame, and provides more pulses for a same bit-rate due to bits saved because of the lack of LTP parameters for the unvoiced frame using a deterministic codebook,

when running on a computer.