LPAS speech coder using vector quantized, multi-codebook, multi-tap pitch predictor and optimized ternary source excitation codebook derivation
A method and apparatus for reducing the complexity of linear prediction analysis-by-synthesis (LPAS) speech coders. The speech coder includes a multi-tap pitch predictor having various parameters and utilizing an adaptive codebook subdivided into at least a first vector codebook and a second vector codebook. The pitch predictor removes certain redundancies in a subject speech signal and vector quantizes the pitch predictor parameters. Further included is a source excitation (fixed) codebook that indicates pulses in the subject speech signal by deriving corresponding vector values. Serial optimization of the adaptive codebook first and then the fixed codebook produces a low complexity LPAS speech coder of the present invention.
1. In a system having working memory and a digital processor, a method for producing a fixed codebook for a speech signal encoder, comprising:
filtering a target speech signal; and
forming entries in the fixed codebook of derived vector values indicating pulses in the filtered target speech signal.
2. The method as claimed in claim 1 further including partitioning the filtered target speech signal into blocks.
3. The method as claimed in claim 2 wherein the blocks are non-overlapping.
4. The method as claimed in claim 2 wherein the blocks are overlapping.
5. The method as claimed in claim 1 wherein the filtering is backward filtering.
6. The method as claimed in claim 1 wherein the vector values are ternary vector values (1, 0, −1).
7. The method as claimed in claim 1 wherein the vector values substantially indicate peak pulse positions in subvectors of the filtered target speech signal.
8. The method as claimed in claim 1 further including considering non-contiguous positions in the filtered target speech signal to determine substantially peak pulse positions in the filtered target speech signal.
9. The method as claimed in claim 1 wherein the derived vector values include sign and position information represented in bits.
10. The method as claimed in claim 9 wherein the number of bits of the derived vector values includes a sign bit plus the number of bits representing, in binary, the number of locations within a subvector at which a peak pulse position is considered.
11. In a system having working memory and a digital processor, a fixed codebook for a speech signal encoder, comprising:
a filter filtering a target speech signal; and
entries in the fixed codebook of derived vector values indicating pulses in the filtered target speech signal.
12. The fixed codebook as claimed in claim 11 wherein the filtered target speech signal is partitioned into blocks.
13. The fixed codebook as claimed in claim 12 wherein the blocks are non-overlapping.
14. The fixed codebook as claimed in claim 12 wherein the blocks are overlapping.
15. The fixed codebook as claimed in claim 11 wherein the filter is a backward filter.
16. The fixed codebook as claimed in claim 11 wherein the vector values are ternary vector values (1, 0, −1).
17. The fixed codebook as claimed in claim 11 wherein the vector values substantially indicate peak pulse positions in subvectors of the filtered target speech signal.
18. The fixed codebook as claimed in claim 11 in which non-contiguous positions in the filtered target speech signal are considered to determine substantially peak pulse positions in the filtered target speech signal.
19. The fixed codebook as claimed in claim 11 wherein the derived vector values include sign and position information represented in bits.
20. The fixed codebook as claimed in claim 19 wherein the number of bits of the derived vector values includes a sign bit plus the number of bits representing, in binary, the number of locations within a subvector at which a peak pulse position is considered.
21. A system for producing a fixed codebook for a speech signal encoder, the system comprising:
an electronic device having a working memory and a digital processor; and
a fixed codebook executable in the working memory by the digital processor, the fixed codebook including:
a filter filtering a target speech signal; and
entries in the fixed codebook of derived vector values indicating pulses in the filtered target speech signal.
22. In a system having working memory and a digital processor, an apparatus for producing a fixed codebook for a speech signal encoder, comprising:
means for filtering a target speech signal; and
means for forming entries in the fixed codebook of derived vector values indicating pulses in the filtered target speech signal.