METHOD OF PRODUCING WHITE NOISE, CONTROL METHOD OF WHITE NOISE AMPLITUDE, AND DIGITAL TELEPHONE SYSTEM

摘要

PROBLEM TO BE SOLVED: To realize a white noise producing method capable of preventing a jar from being generated. SOLUTION: When, a frame to be processed is in a frame error state, a last effective frame before the frame to be processed is full-rated or half-rated, and a mean adaptive code book gain value is less than 0.4 at the time and a mean fixed code book gain value exceeds a threshold, white noise (S(n)) is generated by generating an additional exciting signal by using, instead of the mean fixed code book gain, a prescribed constant with which the amplitude value of an exciting signal after synthesis (Et'(n)) becomes less than a constant value, adding the additional exciting signal to an exciting signal before synthesis (Et(n)) to generate the exciting signal after synthesis (Et'(n)), and processing the exciting signal after synthesis (Et'(n)) by synthesis-filtering operation. Consequently, it is possible to control the amplitude of the white noise (S(n)) by controlling the amplitude of the exciting signal after synthesis (Et'(n)) outputted from a vocoder 4, and prevent jarring noise from being generated.