NOVELTY - Conventionally, the bit rate of a voiceless part of a voice signal is lowered distinguishing the voiceless part from the voiced part; according to the invention, the bit rate of the voiced part is also lowered. The voiced part is constituted of a vowel sound and a consonant sound. The vowel sound can be reproduced with almost no degradation of the quality by reproducing the vocal track component and the pitch component even if the encoding bit rate of the other components is lowered. Therefore, when the vowel sound of the voiced part is encoded, the average bit rate when the voiced part is sounded is lowered by reducing the encoding bits of a noise code book and by lowering the bit rate to a half rate. To discriminate a vowel sound, the relation between the LPC spectrum and the LSP coefficients is used. The vowel sound has high peaks in the LPC spectrum, and the LSP coefficients are present on both sides of the peaks. Therefore, when adjacent LSP coefficients are clos er to each other than a predetermined threshold, it is judged that a peak is present. Such judgment is made for some of the peaks, thereby judging whether or not the sound is a vowel.
USE - Rate control device for variable-rate voice encoding system
DESCRIPTION OF DRAWING(S) - Autocorrelation function coefficient calculating section (10)
LPC calculating section (12)
Rate determining section (11)
LPC-LSP converting section (13)
LSP quantizing section (14)
Voiced sound rate control section (20)
LSP-LPC converting section (15)
Residual signal calculating section (16)
Adaptive code book searching section (17)
Noise code book searching section (18)
Gain quantizing section (19)
