put ffmpeg.exe (easy to find) to the folder with mp3 files, then create a bat script there like this:
@echo off
REM Create output folder if it does not exist
if not exist "adpcm" mkdir adpcm
REM Loop through all mp3 files in current directory
for %%f in (*.mp3) do (
echo Processing "%%f" ...
ffmpeg -i "%%f" -ac 1 -ar 32000 -c:a adpcm_ima_wav "adpcm\%%~nf.wav" -y
)
echo All files converted.
pause |
run it and it will convert mp3 music tracks to 4-bit ADPCM (not resource hungry format). For very low-spec devices like GCW0 you can try -ac 1 -ar 16000 instead.
Also, for more performance (on low-spec devices) it's better to set options in Retroarch like this:
Quick menu -> Options -> Audio -> Mega Drive/Genesis FM = MAME (YM2612)
Quick menu -> Options -> Audio -> Master System FM (YM2612) = OFF
Quick menu -> Options -> Audio -> Audio Filter = OFF
Quick menu -> Options -> System-> CD add-on = none
Main menu -> Audio -> Synchronization = OFF
Main menu -> Audio -> Resamper = nearest & quality lowest
Main menu -> Setting -> Latency = Audio Latency (ms) = 150
