Methods and devices for low-frequency emphasis during audio compression based on ACELP/TCX
First Claim
1. A method for low-frequency emphasizing the spectrum of a sound signal transformed in a frequency domain and comprising transform coefficients grouped in a number of blocks, comprising:
- calculating a maximum energy for one block having a position index;
calculating a factor for each block having a position index smaller than the position index of the block with maximum energy, the calculation of a factor comprising, for each block;
computing an energy of the block; and
computing the factor from the calculated maximum energy and the computed energy of the block; and
for each block, determining from the factor a gain applied to the transform coefficients of the block.
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Abstract
A first aspect of the present invention relates to a method for low-frequency emphasizing the spectrum of a sound signal transformed in a frequency domain and comprising transform coefficients grouped in a number of blocks, in which a maximum energy for one block is calculated and a position index of the block with maximum energy is determined, a factor is calculated for each block having a position index smaller than the position index of the block with maximum energy the calculated maximum energy and the energy of the block, and, for each block, a gain determining from the factor is applied to the transform coefficients of the block. Another aspect of the invention is concerned with an HF coding method for coding, through a bandwidth extension scheme, an HF signal obtained from separation of a full-bandwidth sound signal into the HF signal and a LF signal, in which an estimation of the an HF gain is calculated from LPC coefficients, the energy of the HF signal is calculated, the LF signal is processed to produce a synthesized version of the HF signal, the energy of the synthesized version of the HF signal is calculated, a ratio between the energy of the HF signal and the energy of the synthesized version of the HF signal is calculated and expressing as an HF gain, and a difference between the estimation of the HF gain and the HF gain is calculated to obtain a gain correction. A third aspect of the invention is concerned with a method for producing from a decoded target signal an overlap-add target signal in a current frame coded according to a first coding mode. According to this method, the decoded target signal of the current frame is windowed and a left portion of the window is skipped. A zero-input response of a weighting filter of the previous frame coded according to a second coding mode is calculated and windowed so that the zero-input response has an amplitude monotonically decreasing to zero after a predetermined time period. Finally, the calculated zero-input response is added to the decoded target signal to reconstruct the overlap-add target signal.
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Citations
35 Claims
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1. A method for low-frequency emphasizing the spectrum of a sound signal transformed in a frequency domain and comprising transform coefficients grouped in a number of blocks, comprising:
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calculating a maximum energy for one block having a position index;
calculating a factor for each block having a position index smaller than the position index of the block with maximum energy, the calculation of a factor comprising, for each block;
computing an energy of the block; and
computing the factor from the calculated maximum energy and the computed energy of the block; and
for each block, determining from the factor a gain applied to the transform coefficients of the block. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A device for low-frequency emphasizing the spectrum of a sound signal transformed in a frequency domain and comprising transform coefficients grouped in a number of blocks, comprising:
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means for calculating a maximum energy for one block having a position index;
means for calculating a factor for each block having a position index smaller than the position index of the block with maximum energy, the factor calculating means comprising, for each block;
means for computing an energy of the block; and
means for computing the factor from the calculated maximum energy and the computed energy of the block; and
means for determining, for each block and from the factor, a gain applied to the transform coefficients of the block.
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14. A device for low-frequency emphasizing the spectrum of a sound signal transformed in a frequency domain and comprising transform coefficients grouped in a number of blocks, comprising:
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a calculator of a maximum energy for one block having a position index;
a calculator of a factor for each block having a position index smaller than the position index of the block with maximum energy, wherein the factor calculator, for each block;
computes an energy of the block; and
computes the factor from the calculated maximum energy and the computed energy of the block; and
a calculator of a gain, for each block and in response to the factor, the gain being applied to the transform coefficients of the block. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
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25. A method for processing a received, coded sound signal, comprising:
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extracting coding parameters from the received, coded sound signal, the extracted coding parameters including transform coefficients of a frequency transform of said sound signal, wherein the transform coefficients are grouped in a number of blocks and are low-frequency emphasized using following steps;
(i) calculating a maximum energy for one block having a position index;
(ii) calculating a factor for each block having a position index smaller than the position index of the block with maximum energy, the calculation of a factor comprising, for each block;
computing an energy of the block; and
computing the factor from the calculated maximum energy and the computed energy of the block; and
(iii) for each block, determining from the factor a gain applied to the transform coefficients of the block; and
processing the extracted coding parameters to synthesize the sound signal; and
processing the extracted coding parameters comprising low-frequency de-emphasizing the low-frequency emphasized transform coefficients. - View Dependent Claims (26, 27, 28, 29)
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30. A decoder for processing a received, coded sound signal, comprising:
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an input decoder portion supplied with the received, coded sound signal and implementing an extractor of coding parameters from the received, coded sound signal, the extracted coding parameters including transform coefficients of a frequency transform of said sound signal, wherein the transform coefficients are low-frequency emphasized using a device for low-frequency emphasizing the spectrum of the sound signal transformed in a frequency domain and comprising transform coefficients grouped in a number of blocks, the device including (i) a calculator of a maximum energy for one block having a position index;
(ii) a calculator of a factor for each block having a position index smaller than the position index of the block with maximum energy, wherein the factor calculator, for each block;
(a) computes an energy of the block; and
(b) computes the factor from the calculated maximum energy and the computed energy of the block; and
(iii) a calculator of a gain, for each block and in response to the factor, the gain being applied to the transform coefficients of the block; and
a processor of the extracted coding parameters to synthesize the sound signal, said processor comprising a low-frequency de-emphasis module supplied with the low-frequency emphasized transform coefficients. - View Dependent Claims (31, 32, 33, 34)
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35-92. -92. (canceled)
Specification