SOUND ENCODING/DECODING TYPE ECHO CANCELER

摘要

PURPOSE:To quickly and accurately estimate the impulse response of an echo line with a small amt. of calculation. CONSTITUTION:A code encoded by a CELP system is decoded by a decoder 13 and supplied to a pseudo echo line 24 to be sent to an echo line 23 after D/A conversion. A signal from the echo line 23 is A/D converted, an output from the pseudo echo line 24 is subtracted from the A/D converted signal by an erasing circuit 18 and the result is supplied to a encoder 19. An excitation signal decoded by the decoder 13 is supplied to an impulse response estimating part 25 through a band width enlarging synthetic filter 54. The filter coefficient of the synthesizing filter 54 is set up to a value corresponding to a decoded spectrum envelope parameter, the spectrum envelope of the excitation signal whose frequency characteristic is almost flat is made slightly rugged to form a moderate whitened signal. The signal and the output of the circuit 18 are used for obtaining the estimation of an impulse response by a method similar to a conventional one.