APR9600 noise in playback

Has anybody tried to use separate analog and digital ground and power to reduce the noise with the APR9600. I tested noise by recording external input with no signal. I then can hear some noise when I playback that recording. My demo board has both analog and digital ground and power tied together.

Well I went ahead and wired the digital power and ground separate from the analog power and ground and it made not difference in the background audio noise in playback. It did reduce the high frequency noise seen with an oscilloscope when probing the analog frequencies.

It also looks like the block diagram in the data sheet is not complete. They use the analog in and analog out signals to couple the playback signal into the output stage. That is the reason you need the capacitor between those two signals.

So to reduce the playback noise you need to be sure to use the full input signal range to improve the SNR. I found about 120 mv/pp into the input is best.

I've got great audio quality. Using a larger speaker than the 2.25" inch one I was using made a big difference. But I changed a few capacitors to reduce base distortion also. I recorded a song off a CD onto one channel and it sounds almost a good as AM radio.

My plan is to use this to replace the car "buzzer" and add more warnings to get the drivers attention.

Now I will put a micro on the unit so I can select the channel according to some logic of inputs. The micro would repeat the voice warning three times and then shut off. It would also power down the unit so it draws no power when the car is off. I would probably power the unit up with the key turned to on. You also need to synchronize some warnings after the engine is turned off and the door is opened.