Pulse allocating method in voice coding
A pulse allocating method capable of coding stereophonic voice signals efficiently. In the fixed code note retrievals of this pulse allocating method, for individual subframes, the stereophonic voice signals are compared to judge similarity between channels, and are judged on their characteristics. On the basis of the similarity between the channels and the characteristics of the stereophonic signals, the pulse numbers to be allocated to the individual channels are determined. Pulse retrievals are executed to determine the pulse positions for the individual channels, so that the pulses determined are coded.
1. A pulse apportionment method in a fixed codebook search in speech coding for a stereo speech signal, comprising:
using a comparator, comparing a right channel signal and a left channel signal of the stereo speech signal to determine a similarity between the right channel signal and the left channel signal; and
using a determiner, determining a number of pulses to apportion to the right channel signal and to the left channel signal according to characteristics of the left channel signal and the right channel signal, and the similarity between the left channel signal and the right channel signal.
2. The pulse apportionment method according to claim 1 , wherein, when the similarity is equal to or larger than a threshold value, all pulses are apportioned to one of the right channel signal and the left channel signal.
3. The pulse apportionment method according to claim 1 , wherein the characteristics of the left channel signal and the right channel signal are determined based on at least one of a degree of stationarity, periodicity and maximum autocorrelation factor of each the left channel signal and the right channel signal.
4. The pulse apportionment method according to claim 3 , wherein fewer pulses are apportioned to a channel signal having a larger degree of stationarity, periodicity and maximum autocorrelation factor.
5. The pulse apportionment method according to claim 1 , wherein, when characteristics of the right channel signal and the left channel signal are identical, an equal number of pulses is apportioned to each channel signal.
6. The pulse apportionment method according to claim 1 , wherein a codeword indicating the number of pulses apportioned to each channel is reported to a speech decoder.