Quantization of excitation vector

• US 20060136202A1
• Filed: 12/15/2005
• Published: 06/22/2006
• Est. Priority Date: 12/16/2004
• Status: Abandoned Application

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Sengupta, Anirban
• Application Number:
  US11/300,924
• Publication Number:
  US 20060136202A1
• Time in Patent Office: Days
• US Class Current: 704/222
• CPC Class Codes: G10L 19/12 the excitation function being a code excitation, e.g. in code excited linear prediction [CELP] vocoders

Abstract

A method is disclosed for performing excitation quantization of an input signal using a vector quantization codebook having a plurality of code-vectors, the codebook being associated with a filter system. The method can include determining filter states for the filter system independent of the codebook to define a codebook independent filter system. A quantization error vector for at least a portion of the code-vectors in the codebook is determined based at least in part on the codebook independent filter system. A winning code-vector from the codebook is selected based on predetermined criteria that is functionally related to the determined quantization error vector. The filter memory states of the filter system are updated using the selected winning code-vector.

Claims

1. A method for performing excitation quantization of an input signal using a vector quantization codebook having a plurality of code-vectors, the codebook being associated with a filter system, the method comprising:

determining filter states for the filter system independent of the codebook to define a codebook independent filter system;

determining a quantization error vector for at least a portion of the code-vectors in the codebook based at least in part on the codebook independent filter system;

selecting a winning code-vector from the codebook based on predetermined criteria that is functionally related to the determined quantization error vector; and

updating the filter memory states of the filter system using the selected winning code-vector.

2. The method of claim 1, wherein the determination of the quantization error vector further comprises:

applying the input signal to the codebook independent filter to determine a codebook independent quantization error vector;

applying the at least a portion of code-vectors from the codebook to a predetermined codebook independent filter system having at least one pre-computed codebook independent filter coefficient to determine a codebook independent code-vector for each of the at least a portion of code-vectors from the codebook; and

combining the codebook independent quantization error vector and the codebook independent code-vector to provide the quantization error for the at least a portion of the code-vectors.

3. The method of claim 2, wherein each of the codebook independent code-vectors are determined as a function of a respective code-vector from the codebook and as a function of providing the respective code-vector through the predetermined codebook independent filter system.

4. The method of claim 1, wherein the determination of filter states for the codebook independent filter system further comprises passing a codebook independent residual signal through the filter system;

and

the method further comprises updating the memory of the filter system based on filter memory states that result from passing the codebook independent residual signal through the filter system to provide the codebook independent filter system.

5. The method of claim 4, wherein the input signal is divided into frames, each frame having a plurality of subframes, the codebook independent residual signal being passed through the filter system once per frame, the input signal that is applied to the codebook independent filter comprising a subframe of the input signal, such that a corresponding winning code-vector is selected for each subframe.

6. The method of claim 1, further comprising calculating an energy for each of the determined quantization error vectors, the winning code-vector from the codebook being selected based on the which of the at least a portion of the code-vectors minimizes the energy of the determined quantization error vector.

7. The method of claim 1, wherein the input signal comprises an unquantized speech signal vector that is divided into frames having a plurality of subframes, each subframe including at least two samples.

8. The method of claim 1, wherein the codebook independent filter system is a first codebook independent filter system having a first set of filter states, the method further comprising:

applying the winning code-vector to a second codebook independent filter having at least one codebook independent filter coefficient to determine a second set filter states for the codebook independent filter system; and

calculating filter states for the filter system based on at least a portion of the first set of filter states and the second set of filter states, the calculated filter states being used to update the filter memory states.

9. The method of claim 1, further comprising calculating a new set of filter states as a function of the winning code-vector and filter states associated with the codebook independent filter system.

10. A system for performing excitation quantization of an input signal, comprising:

means for determining a codebook independent filter having filter states that are independent of an associated scaled codebook;

means for determining a winning code-vector candidate from a plurality of code-vector candidates in the codebook based on predetermined criteria that evaluates the code-vector candidates using the codebook independent filter; and

means for updating filter memory with filter states determined based on the winning code-vector candidate.

11. The system of claim 10, further comprising means for determining a quantization error vector based on the codebook independent filter, the means for updating employing the quantization error for the winning code-vector candidate to perform the updating of the filter memory.

12. The system of claim 11, wherein the means for determining a quantization error vector further comprises:

means for determining a codebook independent quantized scaled code-vector based on driving a respective one of the plurality of code-vector candidates to the codebook independent filter;

means for calculating a codebook independent component of the quantization error vector; and

means for combining the codebook independent quantized scaled code-vector and the codebook independent component of the quantization error vector to provide the quantization error vector.

13. The system of claim 11, further comprising:

means for calculating an energy of the quantization error vector for each of the plurality of code-vector candidates; and

means for selecting the winning code-vector candidate according to which of the plurality of code-vector candidates minimizes the energy of the quantization error vector.

14. The system of claim 10, wherein the codebook independent filter has a first set of filter states, the system further comprising:

means for determining a second set filter states for the codebook independent filter system resulting from applying the winning code-vector candidate through the codebook independent filter system; and

means for combining the first set of filter states and the second set of filter states to provide the filter states that are used by the means for updating to update the filter memory.

15. The system of claim 14, wherein the means for determining further comprises means for calculating each filter state in the second set of filter states from respective codebook independent filter update equations that vary as a function of the winning code-vector candidate and are independent of the scaled codebook.

16. The system of claim 10, further comprising means for calculating filter coefficients of a starting filter system independently from the associated codebook based on passing a codebook independent quantized short-term prediction residual signal through the starting filter system, the codebook independent filter being generated from the starting filter system.

17. The system of claim 16, wherein the input signal is divided into frames, each frame having a plurality of subframes, the codebook independent quantized short-term prediction residual signal being passed through the starting filter system once per frame, the input signal that is applied to the codebook independent filter comprising a subframe of the input signal, such that a winning code-vector is selected for each subframe.

18. A system comprising:

a filter system associated with a scaled codebook that has a plurality of code-vectors, the filter system having filter parameters that define respective filter states in corresponding filter memory; and

a codebook search having a first component that configures the filter system independently of the codebook for a given input signal and updates the filter memory to define a codebook independent filter system having corresponding codebook independent filter states, the codebook search having a second component that updates the filter memory with a second set of filter states based on a winning code-vector that is selected from the scaled codebook to substantially minimize energy of a quantization error vector of the filter system, at least a portion of the quantization error vector being determined as a function of the codebook independent filter system.

19. The system of claim 18, further comprising:

a combiner that determines the quantization error vector for at least a substantial portion of the plurality of code-vectors by aggregating a codebook independent quantization error vector, which is generated by applying the input signal to the codebook independent filter system, with a codebook independent code-vector for each of the at least a portion of code-vectors from the codebook, each of the codebook independent code-vector being determined by driving the codebook independent filter system with at least a portion of the code-vectors from the scaled codebook; and

a calculator that determines the energy for the at least a substantial portion of the plurality of code-vectors, which energy is employed to select the winning code-vector.

20. The system of claim 18, further comprising a combiner that determines the second set of filter states by aggregating the first set of filter states of the codebook independent filter system with respective filter state components determined as a function of the winning code-vector and filter coefficients of the codebook independent filter system.