Low-frequency emphasis for LPC-based coding in frequency domain
First Claim
1. Audio encoder for encoding a non-speech audio signal so as to produce therefrom a bitstream, the audio encoder comprising:
- a combination of a linear predictive coding filter comprising a plurality of linear predictive coding coefficients and a time-frequency converter, wherein the combination is configured to filter and to convert a frame of the audio signal into a frequency domain in order to output a spectrum based on the frame and on the linear predictive coding coefficients;
a low frequency emphasizer configured to calculate a processed spectrum based on the spectrum, wherein spectral lines of the processed spectrum representing a lower frequency than a reference spectral line are emphasized;
a control device configured to control the calculation of the processed spectrum by the low frequency emphasizer depending on the linear predictive coding coefficients of the linear predictive coding filter;
a quantization device configured to produce a quantized spectrum based on the processed spectrum;
and a bitstream producer configured to embed the quantized spectrum and the linear predictive coding coefficients into the bitstream.
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Abstract
The invention provides an audio encoder including a combination of a linear predictive coding filter having a plurality of linear predictive coding coefficients and a time-frequency converter, wherein the combination is configured to filter and to convert a frame of the audio signal into a frequency domain in order to output a spectrum based on the frame and on the linear predictive coding coefficients; a low frequency emphasizer configured to calculate a processed spectrum based on the spectrum, wherein spectral lines of the processed spectrum representing a lower frequency than a reference spectral line are emphasized; and a control device configured to control the calculation of the processed spectrum by the low frequency emphasizer depending on the linear predictive coding coefficients of the linear predictive coding filter.
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Citations
30 Claims
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1. Audio encoder for encoding a non-speech audio signal so as to produce therefrom a bitstream, the audio encoder comprising:
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a combination of a linear predictive coding filter comprising a plurality of linear predictive coding coefficients and a time-frequency converter, wherein the combination is configured to filter and to convert a frame of the audio signal into a frequency domain in order to output a spectrum based on the frame and on the linear predictive coding coefficients; a low frequency emphasizer configured to calculate a processed spectrum based on the spectrum, wherein spectral lines of the processed spectrum representing a lower frequency than a reference spectral line are emphasized; a control device configured to control the calculation of the processed spectrum by the low frequency emphasizer depending on the linear predictive coding coefficients of the linear predictive coding filter; a quantization device configured to produce a quantized spectrum based on the processed spectrum; and a bitstream producer configured to embed the quantized spectrum and the linear predictive coding coefficients into the bitstream. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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24. A system comprising an audio encoder for encoding a non-speech audio signal so as to produce therefrom a bitstream and an audio decoder for decoding the bitstream based on the non-speech audio signal so as to produce from the bitstream a non-speech audio output signal,
wherein the audio encoder comprises: -
a combination of a linear predictive coding filter comprising a plurality of linear predictive coding coefficients and a time-frequency converter, wherein the combination is configured to filter and to convert a frame of the audio signal into a frequency domain in order to output a spectrum based on the frame and on the linear predictive coding coefficients; a low frequency emphasizer configured to calculate a processed spectrum based on the spectrum, wherein spectral lines of the processed spectrum representing a lower frequency than a reference spectral line are emphasized; a control device configured to control the calculation of the processed spectrum by the low frequency emphasizer depending on the linear predictive coding coefficients of the linear predictive coding filter; a quantization device configured to produce a quantized spectrum based on the processed spectrum; and a bitstream producer configured to embed the quantized spectrum and the linear predictive coding coefficients into the bitstream; and wherein the audio decoder comprises a bitstream receiver configured to extract the quantized spectrum and the linear predictive coding coefficients from the bitstream; a de-quantization device configured to produce a de-quantized spectrum based on the quantized spectrum; a low frequency de-emphasizer configured to calculate a reverse processed spectrum based on the de-quantized spectrum, wherein spectral lines of the reverse processed spectrum representing a lower frequency than a reference spectral line are deemphasized; and a control device configured to control the calculation of the reverse processed spectrum by the low frequency de-emphasizer depending on the linear predictive coding coefficients comprised in the bitstream.
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25. Method for encoding a non-speech audio signal so as to produce therefrom a bitstream, the method comprising:
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filtering with a linear predictive coding filter comprising a plurality of linear predictive coding coefficients and converting a frame of the audio signal into a frequency domain in order to output a spectrum based on the frame and on the linear predictive coding coefficients; calculating a processed spectrum based on the spectrum, wherein spectral lines of the processed spectrum representing a lower frequency than a reference spectral line are emphasized; and controlling the calculation of the processed spectrum depending on the linear predictive coding coefficients of the linear predictive coding filter; producing a quantized spectrum based on the processed spectrum; and embedding the quantized spectrum and the linear predictive coding coefficients into the bitstream. - View Dependent Claims (26, 27, 28)
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29. Audio decoder for decoding a bitstream based on a non-speech audio signal so as to produce from the bitstream a non-speech audio output signal, the bitstream comprising a quantized spectrum and a plurality of linear predictive coding coefficients, the audio decoder comprising:
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a bitstream receiver configured to extract the quantized spectrum and the linear predictive coding coefficients from the bitstream; a de-quantization device configured to produce a de-quantized spectrum based on the quantized spectrum; a low frequency de-emphasizer configured to calculate a reverse processed spectrum based on the de-quantized spectrum, wherein spectral lines of the reverse processed spectrum representing a lower frequency than a reference spectral line are deemphasized; and a control device configured to control the calculation of the reverse processed spectrum by the low frequency de-emphasizer depending on the linear predictive coding coefficients comprised in the bitstream; wherein the audio decoder comprises combination of a frequency-time converter and an inverse linear predictive coding filter receiving the plurality of linear predictive coding coefficients comprised in the bitstream, wherein the combination is configured to inverse-filter and to convert the reverse processed spectrum into a time domain in order to output the output signal based on the reverse processed spectrum and on the linear predictive coding coefficients.
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30. Audio decoder for decoding a bitstream based on a non-speech audio signal so as to produce from the bitstream a non-speech audio output signal, the bitstream comprising a quantized spectrum and a plurality of linear predictive coding coefficients, the audio decoder comprising:
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a bitstream receiver configured to extract the quantized spectrum and the linear predictive coding coefficients from the bitstream; a de-quantization device configured to produce a de-quantized spectrum based on the quantized spectrum; a low frequency de-emphasizer configured to calculate a reverse processed spectrum based on the de-quantized spectrum, wherein spectral lines of the reverse processed spectrum representing a lower frequency than a reference spectral line are deemphasized; and a control device configured to control the calculation of the reverse processed spectrum by the low frequency de-emphasizer depending on the linear predictive coding coefficients comprised in the bitstream; wherein the control device comprises a spectral analyzer configured to estimate a spectral representation of the linear predictive coding coefficients, a minimum-maximum analyzer configured to estimate a minimum of the spectral representation and a maximum of the spectral representation below a further reference spectral line and a de-emphasis factor calculator configured to calculate spectral line de-emphasis factors for calculating the spectral lines of the reverse processed spectrum representing a lower frequency than the reference spectral line based on the minimum and on the maximum, wherein the spectral lines of the reverse processed spectrum representing a lower frequency than the reference spectral line are de-emphasized by applying the spectral line de-emphasis factors to spectral lines of the spectrum of the de-quantized spectrum representing a lower frequency than the reference spectral line.
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Specification