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If your Module is GPIO18
Download audremap18.dtbo to your pi
sudo cp audremap18.dtbo /boot/overlays/
sudo nano /boot/config.txt
Add this code
dtoverlay=audremap18,pins_18_19
If your Module is GPIO19
Download audremap19.dtbo to your pi
sudo cp audremap19.dtbo /boot/overlays/
sudo nano /boot/config.txt
Add this code
dtoverlay=audremap19,pins_18_19
If your Module is GPIO18&GPIO19
sudo nano /boot/config.txt
Add this code
dtoverlay=audremap,pins_18_19
After rebooting , You need enable local audio
sudo raspi-config  Select System Options -> Audio -> 'headphone'
Go to retropie menu
Select  ->  AUDIO  ->  HEADPHONE
Then reboot again use sudo reboot 
Set audio voice max
Press key START enter retropie MAIN MENU
select SOUND SETTING
->SYSTEM VOLUME 100
->AUDI0 DEVICE   ->  HEADPHONE
->OMX PLAYER AUDIO DEVICE   -> LOCAL
Go back press key B,
Then enter SOUND SETTING ->SYSTEM VOLUME again
You will see it is 97 or 77,You need set it 100 again|
After all setting, the VOLUME will became ok