I just bought a used JM4. Still learning. Perhaps a solution to the MP3 issue is to plug your mp3 play into the mp3 in on the JM4, record the song or a portion of the song using the JM4 record function, then save that recording to the SD card. I assume it would save it as a .WAV file format. Now you could load that song, add overdubs etc. Also note: the newer iPhones did away with the 3.5mm plug in. You'll have to purchase an audio adapter that has 3.5mm male adapter on one end and the iOS lightening adapter. About $6.