Filter Block Since the sound signal from the CPU is a stepped waveform, the filter block is added to smooth the waveform.
CPU MSM6567-15
To mute circuit
Mute Circuit The mute circuit removes noise from the sound signal just before the signal fades away. The circuit detects amplitude of the decaying sound signal by amplifing it by 1000 times, and transistor T6 flows the signal into the ground when the amplitude decays almost zero. +0.5V at the minimum amplitude (no sound) -2.7V at the maximum amplitude Sound signal from filter block
