Variable rate vocoder
First Claim
1. A method of speech signal compression, by variable rate coding of frames of digitized speech samples, comprising the steps of:
- determining a level of speech activity for a frame of digitized speech samples;
selecting an encoding rate from a set of rates based upon said determined level of speech activity for said frame;
coding said frame according to a coding format of a set of coding formats for said selected rate wherein each rate has a corresponding different coding format and wherein each coding format provides for a different plurality of parameter signals representing said digitized speech samples in accordance with a speech model; and
generating for said frame a data packet of said parameter signals.
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Abstract
An apparatus and method for performing speech signal compression, by variable rate coding of frames of digitized speech samples. The level of speech activity for each frame of digitized speech samples is determined and an output data packet rate is selected from a set of rates based upon the determined level of frame speech activity. A lowest rate of the set of rates corresponds to a detected minimum level of speech activity, such as background noise or pauses in speech, while a highest rate corresponds to a detected maximum level of speech activity, such as active vocalization. Each frame is then coded according to a predetermined coding format for the selected rate wherein each rate has a corresponding number of bits representative of the coded frame. A data packet is provided for each coded frame with each output data packet of a bit rate corresponding to the selected rate.
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Citations
48 Claims
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1. A method of speech signal compression, by variable rate coding of frames of digitized speech samples, comprising the steps of:
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determining a level of speech activity for a frame of digitized speech samples; selecting an encoding rate from a set of rates based upon said determined level of speech activity for said frame; coding said frame according to a coding format of a set of coding formats for said selected rate wherein each rate has a corresponding different coding format and wherein each coding format provides for a different plurality of parameter signals representing said digitized speech samples in accordance with a speech model; and generating for said frame a data packet of said parameter signals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. An apparatus for compressing an acoustical signal into variable rate data comprising:
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means for determining a level of audio activity for an input frame of digitized samples of said acoustical signal; means for selecting an output data rate from a predetermined set of rates based upon said determined level of audio activity within said frame; means for coding said frame according to a coding format of a set of coding formats for said selected rate to provide a plurality of parameter signals wherein each rate has a corresponding different coding format with each coding format providing a different plurality of parameter signals representing said digitized speech samples in accordance with a speech model; and means for providing for said frame a corresponding data packet at a data rate corresponding to said selected rate. - View Dependent Claims (19, 20, 21, 22, 23, 24, 25, 26, 27, 28)
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29. A circuit for compressing an acoustical signal into variable rate data comprising:
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a circuit for determining a level of audio activity for an input frame of digitized samples of said acoustical signal; a circuit for selecting an output data rate from a predetermined set of rates based upon said determined level of audio activity within said frame; a circuit for coding said frame according to a coding format of a set of coding formats for said selected rate to provide a plurality of parameter signals wherein each rate has a corresponding different coding format with each coding format providing a different plurality of parameter signals representing said digitized speech samples in accordance with a speech model; and a circuit for providing for said frame a corresponding data packet at a data rate corresponding to said selected rate. - View Dependent Claims (30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47)
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48. A method of speech signal compression by variable rate coding of frames of digitized speech samples comprising the steps of:
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multiplying one frame of digitized speech samples in a sequence of said frames of digitized speech samples by a windowing function to provide a windowed frame of speech data; calculating a set of autocorrelation coefficients from said windowed frame of speech; determining an encoding rate from said set of autocorrelation coefficients; calculating from said set of autocorrelation coefficients a set of linear predictive coding (LPC) coefficients; converting said set of LPC coefficients to a set of line spectral pair values; quantizing said set of line spectral pair (LSP) coefficients in accordance with said rate command and said encoding rate; selecting a pitch value from a predetermined set of pitch values to provide a selected pitch value for each pitch subframe in each frame of digitized speech; quantizing said selected pitch value in accordance with said encoding rate and said rate command; selecting a codebook value from a predetermined set of pitch values to provide a selected pitch value for a pitch frame; quantizing said selected codebook value in accordance with said encoding rate and said rate command; and generating an output data packet comprising said quantized line spectral pair values, quantized selected pitch value, and quantized selected codebook value.
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Specification