PURPOSE: To easily attain required adjustment even in the stage of after- shipment by storing a signal waveform for adjustment to a digital memory, reading a waveform when the adjustment mode is indicated, and inputting the result to any adjustment point of a digital audio processing section.

CONSTITUTION: When the adjustment mode is indicated by the operation of an adjustment mode indication knob 15, an adjustment mode signal is given to a clock recovery circuit 9, a switch circuit 12 and a digital memory 16. The digital memory 16 outputs a digital sinusoidal wave signal based on a clock signal from the clock recovery circuit 9 and it is given to a D/A converter circuit 13. Thus, an analog signal corresponding to the digital sinusoidal wave signal is outputted from the D/A converter circuit 13. On the other hand, the analog signal subject to de-emphasis and low pass filtering is supplied to a speaker equipment, from which the signal is sounded. The operator listening to the sounded sound checks the state of each section to implement the required adjustment.