AUTOMATIC GAIN CONTROL DEVICE

摘要

PROBLEM TO BE SOLVED: To audibly receive objective sound alone at a proper sound volume without any distortion even if the dimension of voice of a speaker or the distance from the speaker to a microphone fluctuates. SOLUTION: After an input signal is processed by a noise suppressing means 100 so that background noise is suppressed, a threshold value serving as a boundary between compression and expansion is decided from an effective value of residual noise after noise suppression for a frame in which noise is determined. Subsequently, for finding a compression ratio in a certain frame, smoothing of effective values of frames including this frame for the last several seconds is carried out. The compression ratio is calculated from the smoothed effective value and multiplied by a necessary gain provided from the threshold value and a target mean effective value so as to be recomposed and outputted to each input frame.