Source: http://www.google.se/patents/US9245532
Timestamp: 2017-09-23 14:44:25
Document Index: 444752291

Matched Legal Cases: ['Application No. 09793768', 'Application No. 09793769', 'Application No. 09793768', 'Application No. 09793770', 'Application No. 2011', 'Application No. 10', 'Application No. 10']

Patent US9245532 - Variable bit rate LPC filter quantizing and inverse quantizing device and method - Google Patent
A device and a method for quantizing a LPC filter in the form of an input vector in a quantization domain, comprises a calculator of a first-stage approximation of the input vector, a subtractor of the first-stage approximation from the input vector to produce a residual vector, a calculator of a weighting...http://www.google.se/patents/US9245532?utm_source=gb-gplus-sharePatent US9245532 - Variable bit rate LPC filter quantizing and inverse quantizing device and method
Publikationsnummer US9245532 B2
Ansökningsnummer US 12/501,201
Publiceringsdatum 26 jan 2016
Registreringsdatum 10 jul 2009
Prioritetsdatum 10 jul 2008
Även publicerat som CA2729665A1, CA2729665C, CA2729751A1, CA2729752A1, CA2972808A1, CA2972812A1, CN102089810A, CN102089810B, CN102119414A, CN102119414B, EP2301021A1, EP2301021A4, EP2301021B1, EP2301022A1, EP2301022A4, EP2301022B1, EP2313887A1, EP2313887A4, US8332213, US8712764, US20100023323, US20100023324, US20100023325, WO2010003252A1, WO2010003253A1, WO2010003253A8, WO2010003254A1
Publikationsnummer 12501201, 501201, US 9245532 B2, US 9245532B2, US-B2-9245532, US9245532 B2, US9245532B2
Uppfinnare Philippe Gournay, Bruno Bessette, Redwan Salami
Ursprunglig innehavare Voiceage Corporation
Citat från patent (99), Citat från andra källor (43), Klassificeringar (8), Juridiska händelser (1)
US 9245532 B2
A device and a method for quantizing a LPC filter in the form of an input vector in a quantization domain, comprises a calculator of a first-stage approximation of the input vector, a subtractor of the first-stage approximation from the input vector to produce a residual vector, a calculator of a weighting function from the first-stage approximation, a warper of the residual vector with the weighting function, and a quantizer of the weighted residual vector to supply a quantized weighted residual vector. A device and a method for inverse quantizing of a LPC filter, comprises means for receiving coded indices representative of a first-stage approximation of a vector representative of the LPC filter in a quantization domain and of a quantized weighted residual version of the vector, a calculator of an inverse weighting function from the first-stage approximation, an inverse quantizer of the quantized weighted residual version of the vector to produce a weighted residual vector, a multiplier of the weighted residual vector by the inverse weighting function to produce a residual vector, and an adder of the first-stage approximation with the residual vector to produce the vector representative of the LPC filter in the quantization domain.
1. A device for quantizing a LPC filter in the form of an input vector in a quantization domain, comprising:
a plurality of quantization modules using respective, distinct quantization modes, wherein the quantization modes include an absolute quantization mode and differential quantization modes, wherein the differential quantization modes use respective, different references each based on a previously quantized LPC filter or a combination of previously quantized LPC filters, and wherein each quantization module comprises:
a calculator of a first-stage approximation of the input vector, wherein the first stage approximation includes (a) the result of absolute quantization of the input vector in the case of the absolute quantization mode and (b) the reference in the case of the differential quantization modes;
a subtractor of the first-stage approximation from the input vector to produce a residual vector;
a calculator of weights of a weighting function using a mathematical relation including the first-stage approximation as a variable;
a warper of the residual vector by applying the weights of the weighting function to the residual vector; and
a quantizer of the weighted residual vector to supply a quantized weighted residual vector; and
a quantization mode selector configured to select one of the quantization modules and the corresponding quantization mode based on a level of distortion.
2. An LPC filter quantizing device according to claim 1, further comprising means for converting the LPC filter in the quantization domain to form the input vector.
3. An LPC filter quantizing device according to claim 1, further comprising a multiplexer of the first-stage approximation of the input vector and the quantized weighted residual vector.
4. An LPC filter quantizing device according to claim 1, wherein the calculator of the weights of the weighting function uses the first-stage approximation and a scaling factor which is dependent upon the quantization mode selected by the quantization mode selector to calculate the weights.
5. An LPC filter quantizing device according to claim 4, wherein the scaling factor has a value chosen to attain at least one of a certain average bit rate and a certain average distortion.
6. An LPC filter quantizing device according to claim 1, wherein the quantization domain is a line spectral frequency domain.
7. An LPC filter quantizing device according to claim 1, wherein the weighting function uses a scaling factor based on a type of the LPC filter and on a selected quantization mode.
8. An LPC filter quantizing device according to claim 1, wherein the quantization mode selector is configured to select the quantization mode providing a lower level of distortion for a given bit rate.
9. An LPC filter quantizing device according to claim 1, wherein the quantization mode selector is configured to select the quantization mode providing a lower bit rate for a target level of distortion.
10. A device for quantizing a LPC filter in the form of an input vector in a quantization domain, comprising:
a quantization mode selector configured to select one of the quantization modules and the corresponding quantization mode based on a level of distortion;
wherein, in each of the quantization modules, the quantizer of the weighted residual vector comprises a variable bit rate quantizer.
11. An LPC filter quantizing device according to claim 10, wherein the variable bit rate quantizer comprises an algebraic vector quantizer.
12. A device for inverse quantizing a LPC filter quantized in an encoder, in the form of an input vector in a quantization domain, by a LPC filter quantizing device comprising (a) a plurality of quantization modules using respective, distinct quantization modes, wherein the quantization modes include an absolute quantization mode and differential quantization modes, wherein the differential quantization modes use respective, different references each based on a previously quantized LPC filter or a combination of previously quantized LPC filters, and wherein each quantization module comprises (i) a calculator of a first-stage approximation of the input vector, wherein the first stage approximation includes the result of absolute quantization of the input vector in the case of the absolute quantization mode and the reference in the case of the differential quantization modes, (ii) a subtractor of the first-stage approximation from the input vector to produce a residual vector, (iii) a calculator of weights of a weighting function using a mathematical relation including the first-stage approximation as a variable, (iv) a warper of the residual vector by applying the weights of the weighting function to the residual vector, and (v) a quantizer of the weighted residual vector to supply a quantized weighted residual vector; and (b) a quantization mode selector configured to select one of the quantization modules and the corresponding quantization mode based on a level of distortion, the LPC filter inverse quantizing device comprising:
a demultiplexer for receiving, from the encoder, and for demultiplexing coded indices representative of (a) the first-stage approximation from the selected quantization module, (b) the selected quantization mode, and (c) the quantized weighted residual vector from the selected quantization module;
a determiner of the selected quantization mode using the demultiplexed coded indices;
a calculator of the first-stage approximation in response to the demultiplexed coded indices, and as a function of the determined quantization mode;
a calculator of an inverse weighting function from the first-stage approximation;
an inverse quantizer of the quantized weighted residual vector responsive to the demultiplexed coded indices to produce a weighted residual vector;
a multiplier of the weighted residual vector by the inverse weighting function to produce a residual vector; and
an adder of the first-stage approximation with the residual vector to produce a vector representative of the LPC filter in the quantization domain.
13. An LPC filter inverse quantizing device according to claim 12, wherein the inverse quantizer comprises a variable bit rate inverse algebraic vector quantizer.
14. An LPC filter inverse quantizing device according to claim 12, wherein the quantization domain is a line spectral frequency domain.
15. A method implemented in an encoder for quantizing a LPC filter in the form of an input vector in a quantization domain, comprising:
providing a plurality of distinct quantization modes, wherein the quantization modes include an absolute quantization mode and differential quantization modes, wherein the differential quantization modes use respective, different references each based on a previously quantized LPC filter or a combination of previously quantized LPC filters;
performing, for each of the plurality of distinct quantization modes, the following operations:
computing a first-stage approximation of the input vector, wherein the first stage approximation includes (a) the result of absolute quantization of the input vector in the case of the absolute quantization mode and (b) the reference in the case of the differential quantization modes;
subtracting the first-stage approximation from the input vector to produce a residual vector;
calculating weights of a weighting function using a mathematical relation including the first-stage approximation as a variable;
applying the weights of the weighting function to the residual vector; and
quantizing the weighted residual vector to supply a quantized weighted residual vector;
selecting one of the quantization modes based on a level of distortion; and
transmitting from the encoder to a decoder the selected quantization mode, the first-stage approximation of the input vector obtained using the selected quantization mode, and the quantized weighted residual vector obtained using the selected quantization mode.
16. An LPC filter quantizing method according to claim 15, further comprising converting the LPC filter in the quantization domain to form the input vector.
17. An LPC filter quantizing method according to claim 15, further comprising multiplexing the first-stage approximation of the input vector and the quantized weighted residual vector obtained using the selected quantization mode.
18. An LPC filter quantizing method according to claim 15, wherein calculating the weights of the weighting function comprises using the first-stage approximation and a scaling factor which is dependent upon the selected quantization mode.
19. An LPC filter quantizing method according to claim 18, wherein the scaling factor has a value chosen to attain at least one of a certain average bit rate and a certain average distortion.
20. An LPC filter quantizing method according to claim 15, wherein the quantization domain is a line spectral frequency domain.
21. A method implemented in an encoder for quantizing a LPC filter in the form of an input vector in a quantization domain, comprising:
transmitting from the encoder to a decoder the selected quantization mode, the first-stage approximation of the input vector obtained using the selected quantization mode, and the quantized weighted residual vector obtained using the selected quantization mode;
wherein quantizing the weighted residual vector comprises using a variable bit rate quantizer.
22. An LPC filter quantizing method according to claim 21, wherein using the variable bit rate quantizer comprises using an algebraic vector quantizer.
23. A method implemented in a decoder for inverse quantizing a LPC filter quantized in an encoder, in the form of an input vector in a quantization domain, by a LPC filter quantizing method comprising (a) providing a plurality of distinct quantization modes, wherein the quantization modes include an absolute quantization mode and differential quantization modes, wherein the differential quantization modes use respective, different references each based on a previously quantized LPC filter or a combination of previously quantized LPC filters, (b) performing, for each of the plurality of distinct quantization modes, the following operations: (i) computing a first-stage approximation of the input vector, wherein the first stage approximation includes the result of absolute quantization of the input vector in the case of the absolute quantization mode and the reference in the case of the differential quantization modes, (ii) subtracting the first-stage approximation from the input vector to produce a residual vector, (iii) calculating weights of a weighting function using a mathematical relation including the first-stage approximation as a variable, (iv) applying the weights of the weighting function to the residual vector, and (v) quantizing the weighted residual vector to supply a quantized weighted residual vector, (c) selecting one of the quantization modes based on a level of distortion, and (d) transmitting from the encoder to the decoder the selected quantization mode, the first-stage approximation of the input vector obtained using the selected quantization mode, and the quantized weighted residual vector obtained using the selected quantization mode, the LPC filter inverse quantizing method comprising:
receiving at the decoder, from the encoder, coded indices representative of (a) the first-stage approximation from the selected quantization mode, (b) the selected quantization mode, and (c) the quantized weighted residual vector from the selected quantization mode;
determining the selected quantization mode using the received coded indices;
calculating, in response to the received coded indices, the first-stage approximation as a function of the determined quantization mode;
calculating an inverse weighting function from the first-stage approximation;
inverse quantizing the quantized weighted residual vector in response to the received coded indices to produce a weighted residual vector;
applying the inverse weighting function to the weighted residual vector to produce a residual vector; and
adding the first-stage approximation with the residual vector to produce a vector representative of the LPC filter in the quantization domain.
24. An LPC filter inverse quantizing method according to claim 23, wherein receiving the coded indices comprises demultiplexing the coded indices.
25. An LPC filter inverse quantizing method according to claim 23, wherein inverse quantizing the quantized weighted residual vector comprises variable bit rate inverse algebraic vector quantizing the quantized weighted residual vector.
26. An LPC filter inverse quantizing method according to claim 23, wherein applying the inverse weighting function to the weighted residual vector comprises multiplying the weighted residual vector by the inverse weighting function.
27. An LPC filter inverse quantizing method according to claim 23, wherein the quantization domain is a line spectral frequency domain.
28. An LPC filter quantizing device according to claim 7, wherein a combination of the type of LPC filter, of the quantization mode, and of the first-stage approximation is selected from the group consisting of:
LPC4 filter, with absolute quantization, and with 8-bit vector quantization (VQ) approximation;
LPC0 filter, with absolute quantization, and with 8-bit VQ approximation;
LPC0 filter, with relative LPC4 quantization, and with quantized LPC4 approximation;
LPC2 filter, with absolute quantization, and with 8-bit VQ approximation;
LPC2 filter, with relative LPC4 quantization, and with quantized LPC4 approximation;
LPC1 filter, with absolute quantization, and with 8-bit VQ approximation;
LPC1 filter, with relative (LPC0+LPC2)/2 quantization, and with quantized (LPC0+LPC2)/2 approximation;
LPC1 filter, with relative LPC2 quantization, and with quantized LPC2 approximation;
LPC3 filter, with absolute quantization, and with 8-bit VQ approximation;
LPC3 filter, with relative (LPC2+LPC4)/2 quantization, and with quantized (LPC2+LPC4)/2 approximation;
LPC3 filter, with relative LPC2 quantization, and with quantized LPC2 approximation; and
LPC3 filter, with relative LPC4 quantization, and with quantized LPC4 approximation;
wherein the LPC0 filter is the LPC filter of a last frame of a previous super-frame, the LPC1 filter is the LPC filter of a first frame of a current super-frame, the LPC2 filter is the LPC filter of a second frame of the current super-frame, the LPC3 filter is the LPC filter of a third frame of the current super-frame and the LPC4 filter is the LPC filter of a fourth frame of the current super-frame.
The present invention relates to coding and decoding of a sound signal, for example an audio signal. More specifically, but not exclusively, the present invention relates to variable bit rate LPC (Linear Prediction Coefficients) filter quantizing and inverse quantizing device and method.
Code-Excited Linear Prediction (CELP) coding is one of the best techniques for achieving a good compromise between subjective quality and bit rate. The CELP coding technique is a basis for several speech coding standards both in wireless and wireline applications. In CELP coding, the speech signal is sampled and processed in successive blocks of L samples usually called frames, where L is a predetermined number of samples corresponding typically to 10-30 ms of speech. A linear prediction LP) filter is computed and transmitted every frame; the LP filter is also known as LPC (Linear Prediction Coefficients) filter. The computation of the LPC filter typically uses a lookahead, for example a 5-15 ms speech segment from the subsequent frame. The L-sample frame is divided into smaller blocks called subframes. In each subframe, an excitation signal is usually obtained from two components, a past excitation and an innovative, fixed-codebook excitation. The past excitation is often referred to as the adaptive-codebook or pitch-codebook excitation. The parameters characterizing the excitation signal are coded and transmitted to the decoder, where the excitation signal is reconstructed and used as the input of the LPC filter.
According to non-restrictive illustrative embodiments of the present invention, there are provided:
A device for quantizing a LPC filter in the form of an input vector in a quantization domain, comprising: means for computing a first-stage approximation of the input vector; means for subtracting the first-stage approximation from the input vector to produce a residual vector; means for calculating a weighting function from the first-stage approximation; means for applying the weighting function to the residual vector; and means for quantizing the weighted residual vector to supply a quantized weighted residual vector.
A device for quantizing a LPC filter in the form of an input vector in a quantization domain, comprising: a calculator of a first-stage approximation of the input vector; a subtractor of the first-stage approximation from the input vector to produce a residual vector; a calculator of a weighting function from the first-stage approximation; a warper of the residual vector with the weighting function; and a quantizer of the weighted residual vector to supply a quantized weighted residual vector.
A device for quantizing a LPC filter in the form of an input vector in a quantization domain, comprising: a calculator of a first-stage approximation of the input vector; a subtractor of the first-stage approximation from the input vector to produce a residual vector; a calculator of a weighting function from the first-stage approximation; a warper of the residual vector with the weighting function; and a quantizer of the weighted residual vector to supply a quantized weighted residual vector. The calculator of the first-stage approximation is selected from the group consisting of: an absolute quantizer of the input vector; a quantizer of a previous LPC vector; a quantizer of a future LPC vector; and an interpolator of previous quantized and/or future quantized LPC vectors; to give an estimate of the input vector.
A device for quantizing a LPC filter in the form of an input vector in a quantization domain, comprising: a calculator of a first-stage approximation of the input vector; a subtractor of the first-stage approximation from the input vector to produce a residual vector; a calculator of a weighting function from the first-stage approximation; a warper of the residual vector with the weighting function; and a quantizer of the weighted residual vector to supply a quantized weighted residual vector. The calculator of the weighting function calculates different weights, and the warper applies the different weights to components of the residual vector.
A device for quantizing a LPC filter in the form of an input vector in a quantization domain, comprising: a calculator of a first-stage approximation of the input vector; a subtractor of the first-stage approximation from the input vector to produce a residual vector; a calculator of a weighting function from the first-stage approximation; a warper of the residual vector with the weighting function; and a quantizer of the weighted residual vector to supply a quantized weighted residual vector. The quantizer of the weighted residual vector comprises a variable bit rate quantized.
A device for inverse quantizing of a LPC filter, comprising: means for receiving coded indices representative of a first-stage approximation of a vector representative of the LPC filter in a quantization domain, and a quantized weighted residual version of the vector; means for calculating an inverse weighting function from the first-stage approximation; means for inverse quantizing the quantized weighted residual version of the vector to produce a weighted residual vector; means for applying the inverse weighting function to the weighted residual vector to produce a residual vector; and means for adding the first-stage approximation with the residual vector to produce the vector representative of the LPC filter in the quantization domain.
A device for inverse quantizing of a LPC filter, comprising: means for receiving coded indices representative of a first-stage approximation of a vector representative of the LPC filter in a quantization domain, and a quantized weighted residual version of the vector; a calculator of an inverse weighting function from the first-stage approximation; an inverse quantizer of the quantized weighted residual version of the vector to produce a weighted residual vector; a multiplier of the weighted residual vector by the inverse weighting function to produce a residual vector; and an adder of the first-stage approximation with the residual vector to produce the vector representative of the LPC filter in the quantization domain.
A device for inverse quantizing of a LPC filter, comprising: means for receiving coded indices representative of a first-stage approximation of a vector representative of the LPC filter in a quantization domain, and a quantized weighted residual version of the vector; a calculator of an inverse weighting function from the first-stage approximation, an inverse quantizer of the quantized weighted residual version of the vector to produce a weighted residual vector; a multiplier of the weighted residual vector by the inverse weighting function to produce a residual vector; and an adder of the first-stage approximation with the residual vector to produce the vector representative of the LPC filter in the quantization domain. The received coded indices include an index representative of a quantization mode.
A device for inverse quantizing of a LPC filter, comprising: means for receiving coded indices representative of a first-stage approximation of a vector representative of the LPC filter in a quantization domain, and a quantized weighted residual version of the vector; a calculator of an inverse weighting function from the first-stage approximation; an inverse quantizer of the quantized weighted residual version of the vector to produce a weighted residual vector; a multiplier of the weighted residual vector by the inverse weighting function to produce a residual vector; and an adder of the first-stage approximation with the residual vector to produce the vector representative of the LPC filter in the quantization domain. The inverse quantizer of the quantized weighted residual version of the vector comprises a variable bit rate inverse quantizer.
A method for quantizing a LPC filter in the form of an input vector in a quantization domain, comprising: computing a first-stage approximation of the input vector; subtracting the first-stage approximation from the input vector to produce a residual vector; calculating a weighting function from the first-stage approximation; applying the weighting function to the residual vector; and quantizing the weighted residual vector to supply a quantized weighted residual vector.
A method for quantizing a LPC filter in the form of an input vector in a quantization domain, comprising: computing a first-stage approximation of the input vector; subtracting the first-stage approximation from the input vector to produce a residual vector; calculating a weighting function from the first-stage approximation; applying the weighting function to the residual vector; and quantizing the weighted residual vector to supply a quantized weighted residual vector. Computing the first-stage approximation is selected from the group consisting of: absolute quantizing of the input vector; quantizing of a previous LPC vector; quantizing of a future LPC vector; and interpolating of previous quantized and/or future quantized LPC vectors to give an estimate of the input vector.
A method for quantizing a LPC filter in the form of an input vector in a quantization domain, comprising: computing a first-stage approximation of the input vector; subtracting the first-stage approximation from the input vector to produce a residual vector; calculating a weighting function from the first-stage approximation; applying the weighting function to the residual vector; and quantizing the weighted residual vector to supply a quantized weighted residual vector. Calculating a weighting function comprises calculating different weights, and applying the weighting function comprises applying the different weights to components of the residual vector.
A method for quantizing a LPC filter in the form of an input vector in a quantization domain, comprising: computing a first-stage approximation of the input vector; subtracting the first-stage approximation from the input vector to produce a residual vector; calculating a weighting function from the first-stage approximation; applying the weighting function to the residual vector; and quantizing the weighted residual vector to supply a quantized weighted residual vector. Quantizing the weighted residual vector comprises using a variable bit rate quantizer.
A method for inverse quantizing of a LPC filter, comprising: receiving coded indices representative of a first-stage approximation of a vector representative of the LPC filter in a quantization domain, and a quantized weighted residual version of the vector; calculating an inverse weighting function from the first-stage approximation; inverse quantizing the quantized weighted residual version of the vector to produce a weighted residual vector; applying the inverse weighting function to the weighted residual vector to produce a residual vector; and adding the first-stage approximation with the residual vector to produce the vector representative of the LPC filter in the quantization domain.
A method for inverse quantizing of a LPC filter, comprising: receiving coded indices representative of a first-stage approximation of a vector representative of the LPC filter in a quantization domain, and a quantized weighted residual version of the vector; calculating an inverse weighting function from the first-stage approximation; inverse quantizing the quantized weighted residual version of the vector to produce a weighted residual vector; applying the inverse weighting function to the weighted residual vector to produce a residual vector; and adding the first-stage approximation with the residual vector to produce the vector representative of the LPC filter in the quantization domain. The received coded indices include an index representative of a quantization mode.
A method for inverse quantizing of a LPC filter, comprising: receiving coded indices representative of a first-stage approximation of a vector representative of the LPC filter in a quantization domain, and a quantized weighted residual version of the vector; calculating an inverse weighting function from the first-stage approximation; inverse quantizing the quantized weighted residual version of the vector to produce a weighted residual vector; applying the inverse weighting function to the weighted residual vector to produce a residual vector; and adding the first-stage approximation with the residual vector to produce the vector representative of the LPC filter in the quantization domain. Inverse quantizing the quantized weighted residual version of the vector comprises variable bit rate inverse quantizing the quantized weighted residual version of the vector.
the result of extrapolation or interpolation operations applied to past or future quantized LPC filters; or
any quantized value available both at the encoder and the decoder.
Operations 102 and 103 1, 103 2, . . . , 103 n: Still referring to FIG. 1, the input LPC filter 101 is supplied to an absolute quantizer (Operation 102) and to differential quantizers (Operations 103 1, 103 2, . . . , 103 n). The absolute quantizer (Operation 102) quantizes the absolute value (not a difference) of the input LPC filter 101. The differential quantizers (Operations 103 1, 103 2, . . . , 103 n) are designed to differentially quantize the input LPC filter 101 with respect to respective references 1, 2, . . . n.
Operation 105: Following the selection of one of the references 1, 2, . . . , n by the Operation 104, a transmitter (Operation 105) communicates or signals to the decoder (not shown) the quantized LPC filter (not shown) and an index indicative of the quantization mode (sub-operation 1051), for example absolute or differential quantization. Also, when differential quantization is used, the transmitter (Operation 105) communicates or signals to the decoder indices representative of the selected reference and associated differential quantizer of Operations 103 1, 103 2, . . . , 103 n (sub-operation 105 2). Some specific bits are transmitted to the decoder for such signaling.
ACELP (covering a duration of one (1) frame);
TCX256 (covering a duration of one (1) frame);
For a given super-frame, the combination of modes which minimizes a total weighted error is determined by a “closed-loop” mode selection procedure. More specifically, instead of testing the 26 combinations, the selection of the mode is performed through eleven (11) different trials (tree search, see Table 1). In AMR-WB+ codec, the closed-loop selection is based on minimizing the mean-squared error between the input and codec signal in a weighted domain (or maximizing the signal to quantization noise ratio).
7 TCX256
Operation 502: Operation 512 is optional and used in a first LPC-based coding frame after a non-LPC-based coding frame. An absolute quantizer quantizes the filter LPC0 or a differential quantizer differentially quantizes the filter LPC0 relative to the quantized filter LPC4. The filter LPC0 is the last LPC filter (LPC4) from the previous super-frame and can be used as a possible reference for quantizing the filters LPC1 to LPC4.
Operation 503: An absolute quantizer quantizes the filter LPC2 or a differential quantizer differentially quantizes the filter LPC2 relative to the quantized filter LPC4 used as reference.
Operation 504: An absolute quantizer quantizes the filter LPC1, a differential quantizer differentially quantizes the filter LPC1 relative to the quantized filter LPC2 used as reference, or a differential quantizer differentially quantizes the filter LPC1 relative to (quantized filter LPC2+quantized filter LPC0)/2) used as reference.
Operation 505: An absolute quantizer quantizes the filter LPC3, a differential quantizer differentially quantizes the filter LPC3 relative to the quantized filter LPC2 used as reference, a differential quantizer differentially quantizes the filter LPC3 relative to quantized filter LPC4 used as reference, or a differential quantizer differentially quantizes the filter LPC3 relative to (quantized filter LPC2+quantized filter LPC4)/2) used as reference.
means for receiving and extracting from the received bitstream, for example a demultiplexer, the quantized filter LPC2 and the index indicative of one of the absolute quantization mode and the differential quantization mode; and
an absolute inverse quantizer supplied with the quantized filter LPC2 and the index indicative of the absolute quantization mode for inverse quantizing the quantized filter LPC2, or a differential inverse quantizer supplied with the quantized filter LPC2 and the index indicative of the differential quantization mode for inverse quantizing the quantized filter LPC2.
wt ( i ) = 1 d i + 1 d i + 1 , i = 0 , … , p - 1
d 0 =f(0)
d p =SF/2−f(p−1)
d i =f(i)−f(i−1),i=1, . . . , p−1
r(i)=f(i)−f 1st(i),i=0, . . . ,p−1
w ( i ) = 1 W ⋆ 400 d i · d i + 1 , i = 0 , … , p - 1
d 0 =f 1st(0)
d p =SF/2−f 1st(p−1)
In Operations 804, 804 1, 804 2, . . . , 804 n, a warper multiplies the residual LSF vector from the Operations 802, 802 1, 802 2, . . . , 802 n, respectively, by the weighting function from the Operations 803, 803 1, 803 2, . . . 803 n, respectively.
In Operations 805, 805 1, 805 2, . . . , 805 n a variable bit rate quantizer, for example an algebraic vector quantizer (AVQ) quantizes the resulting weighted residual LSF vector from the Operations 804, 804 1, 804 2, . . . , 804 n, respectively, to supply a quantized weighted residual LSF vector.
A possible algebraic vector quantizer (AVQ) used for example in Operation 605 of FIG. 6 and Operations 805, 805 1, 805 2, . . . , 805 n of FIG. 8 is based on the 8-dimensional RE8 lattice vector quantizer used to quantize the spectrum in TCX modes of AMR-WB+[1].
RE 8=2D 8∪{2D 8+(1, . . . ,1)}
that is as the union of a lattice 2D8 and a version of the lattice 2D8 shifted by the vector (1, 1, 1, 1, 1, 1, 1, 1). Therefore, searching for the nearest neighbour in the lattice RE8 is equivalent to searching for the nearest neighbour in the lattice 2D8, then searching for the nearest neighbour in the lattice 2D8+(1, 1, 1, 1, 1, 1, 1, 1), and finally selecting the best of those two lattice points. The lattice 2D8 is the lattice D8 scaled by a factor of 2, with the lattice D8 defined as:
D 8={(x 1 , . . . ,x 8)εZ 8 |x 1 + . . . +x 8 is even}
3. y1k=2 z k
if z k(I)−y1k(I)<0, then y1k(I)=y1k(I)−2
if z k(I)−y1k(I)>0, then y1k(I)=y1k(I)+2
if z k(I)−y2k(I)<0, then y2k(I)=y2k(I)−2
if z k(I)−y2k(I)>0, then y2k(I)=y2k(I)+2
In the present case, the base codebook C in the LPC quantizer can be either codebook Q0, Q2, Q3 or Q4 from Reference [6]. When a given lattice point ck is not included in these base codebooks, the Voronoi extension is applied, using this time only the codebook Q3 or Q4. Note that here, Q2⊂Q3 but Q3⊂/Q4.
If ck is an element of the base codebook C, the index used to encode ck is thus the codebook number nk plus the index Ik of the codevector ck in the codebook Qn k . The codebook number nk is encoded as described in a third operation. The index Ik indicates the rank of the codevector ck, i.e. the permutation to be applied to a specific leader to obtain ck (see Reference [7]). If nk=0, then Ik uses no bits. Otherwise, the index Ik uses 4nk bits.
k=modM(c k G −1).
V3 Compute the difference vector w=ck−v. This difference vector w always belongs to the scaled lattice mΛ, where Λ is the lattice RE8. Compute z=w/M, i.e., apply the inverse scaling to the difference vector w. The codevector z belongs to the lattice Λ since w belongs to MΛ.
As mentioned herein above, the actual number of quantized LPC filters coded within the bitstream depends on the ACELP/TCX mode combination of the super-frame. The ACELP/TCX mode combination is extracted from the bitstream and determines the coding modes, mod [k] for k=0 to 3, of each of the four (4) frames composing the super-frame. The mode value is 0 for ACELP, 1 for TCX256, 2 for TCX512, 3 for TCX1024.
c) if the quantized sub-vector Bk (a lattice point in lattice RE8) was not in the base codebook, the 8 indices of the Voronoi extension index vector k calculated in sub-operation V1 of the second operation of the above described algebraic vector quantization; from the Voronoi extension indices, an extension vector v can be computed as taught by Reference [8]. The number of bits in each component of index vector k is given by the extension order r, which can be obtained from the code value of index nk. The scaling factor M of the Voronoi extension is given by M=2r.
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