Are you recording from an audio line input or from a microphone? You might try an "anti-pop" resistor across the input. To reduce the hiss, try a low-pass filter.
How are you configuring the APC register?
At what frequency are you running the ISD?
Pay especial attention to bypassing (lots of it!) and to power and ground routing.Such as circuit design and layout to enable me to get the best from these chips.
I would like to see a copy of that old application sheet if possible.I have added a lm386 audio amp using an old winbond application sheet.
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