Codebook sharing for LSF quantization
View Patent ↗In accordance with one aspect of the invention, a selector supports the selection of a first encoding scheme or the second encoding scheme based upon the detection or absence of the triggering characteristic in the interval of the input speech signal. The first encoding scheme has a pitch pre-processing procedure for processing the input speech signal to form a revised speech signal biased toward an ideal voiced and stationary characteristic. The pre-processing procedure allows the encoder to fully capture the benefits of a bandwidth-efficient, long-term predictive procedure for a greater amount of speech components of an input speech signal than would otherwise be possible. In accordance with another aspect of the invention, the second encoding scheme entails a long-term prediction mode for encoding the pitch on a sub-frame by sub-frame basis. The long-term prediction mode is tailored to where the generally periodic component of the speech is generally not stationary or less than completely periodic and requires greater frequency of updates from the adaptive codebook to achieve a desired perceptual quality of the reproduced speech under a long-term predictive procedure.
1. A multi-rate speech coding system capable of operating in one of a first coding rate and a second coding rate, the multi-rate speech coding system comprising:
a vector quantizer (VQ) for quantizing line spectral frequencies (LSFs), the VQ including a first VQ stage and a second VQ stage;
a processing circuitry configured to:
determine whether the multi-rate speech coding system is configured to operate in the first coding rate or the second coding rate;
quantize the LSFs using the first VQ stage and not the second VQ stage when the processing circuitry determines that the multi-rate speech coding system is configured to operate in the first coding rate; and
quantize the LSFs using both the first VQ stage and the second VQ stage when the processing circuity determines that the multi-rate speech coding system is configured to operate in the second coding rate.
2. The multi-rate speech coding system of claim 1 further capable of operating in a third coding rate, wherein the processing circuitry is further configured to determine whether the multi-rate speech coding system is configured to operate in the first coding rate, the second coding rate or the third coding rate, and wherein the processing circuitry is further configured to quantize the LSFs using both the first VQ stage and the second VQ stage when the processing circuitry determines that the multi-rate speech coding system is configured to operate in the third coding rate.
3. The multi-rate speech coding system of claim 1 , wherein the processing circuitry is further configured to use a predictive coding at the first coding rate and the second cording rate to quantize the LSFs.
4. The multi-rate speech coding system of claim 1 , wherein the processing circuitry is configured to quantize the LSFs by minimizing a weighted distortion measure.
5. The multi-rate speech coding system of claim 4 , wherein the weighted distortion measure uses weights based on the LSFs.
6. A quantization method for use by a multi-rate speech coding system capable of operating in one of a first coding rate and a second coding rate, multi-rate speech coding system including a vector quantizer (VQ) for quantizing line spectral frequencies (LSFs), the VQ including a first VQ stage and a second VQ stage, the quantization method comprising:
determining whether the multi-rate speech coding system is operating in the first coding rate or the second coding rate;
quantizing the LSFs using the first VQ stage and not using the second VQ stage when the determining determines that the multi-rate speech coding system is configured to operate in the first coding rate; and
quantizing the LSFs using both the first VQ stage and the second VQ stage when the determining determines that the multi-rate speech coding system is configured to operate in the second coding rate.
7. The method of claim 6 , wherein the multi-rate speech coding system is further capable of operating in a third coding rate, and wherein the method further comprises:
determining whether the multi-rate speech coding system is operating in the first coding rate, the second coding rate or the third coding rate;
quantizing the LSFs using both the first VQ stage and the second VQ stage when the determining determines that the multi-rate speech coding system is configured to operate in the third coding rate.
8. The method of claim 6 further comprising:
using a predictive coding at the first coding rate and the second coding rate for the quantizing of the LSFs.
9. The method of claim 6 , wherein the quantizing of the LSFs includes minimizing a weighted distortion measure.
10. The method of claim 9 , wherein the weighted distortion measure uses weights based on the LSFs.
11. The multi-rate speech coding system of claim 2 , wherein the multi-rate speech coding system is in a pitch preprocessing mode (PP_mode) while configured for operation in the first coding rate or the second coding rate, and wherein the multi-rate speech coding system is in one of the PP_mode and a long-term prediction mode (LTP 13 mode) while configured for operation in the third coding rate.
12. The method of claim 6 , wherein the multi-rate speech coding system is in a pitch preprocessing mode (PP_mode) while configured for operation in the first coding rate or the second coding rate, and wherein the multi-rate speech coding system is in one of the PP_mode and a long-term prediction mode (LTP_mode) while configured for operation in the third coding rate.