Song --> Wav --> MP3
Go to the song page.
Hit Convert.
Convert the song to a Sequence.
Hit the main button.
Then make that the active sequence.
Then go to the record page.
Record from the out's (forgot the option - dont have my mpc in front of me).
Hit record F button (F4, F5 or F6 or something like that)
Then hit PlayStart on your mpc.
The sequence will be recorded to a Wav File.
Go to the save dialog. Save the new "Sample" as a file. It will be quite large.
Connect your PC to your MPC through the USB cable.
The computer will recognize the "new drive" probably something like "Removable Drive" if you use Windows.
To see it, open My Computer.
Open the drive.
Navigate to where you saved it.
Download Audacity or use your favorite DAW (Digital Audio Workstation) or download a coverter such as one listed here (FREE):
http://www.nch.com.au/switch/Open the said program.
If audacity, open the WAV and do a Save As (i think) and choose MP3
If using the coverter, choose the file and covert to type Mp3.
Convert the file to MP3.
You're done.
Now smack yourself.