The sounds in that MP3 file are horrible. Terrible and horrible. There is a very sharp harsh low frequency tone going on in the piece that grates the ears as well. That sound sample is at least five times worse than the elementary tones you'd hear out of a 1970's electronic pinball machine.

Is this what the client gave you? Or us this what you recorded from the "electronic organ" hobby circuit that you built?

If that came from the client then I suggest you lean heavy toward convincing them that you need to build up a MIDI player. You should be able to find some MIDI examples on the WEB using microcontrollers. From things I read some years back you should be able to get an MCU to play MIDI notes from multiple channels at one time so that you can a more full and decent sound. If your client is adamant that you keep using your older style Atmel MCU then maybe you should consider putting two of them on the board. One to manage the basic functionality and the other to be a dedicated MIDI player. See if you can get it to support 8 to 10 multiple notes at a time!

Mike Karas