Use a fake radio with 4 buttons on the top connected to the computer. The audio can come
from the computer depending upon which button is pressed. You could probably use buttons
from a cheap MIDI keyboard or a similar controller.
If you want sound to come
from the radio then just put a speaker in it connected to the computer.
James.
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JRP Music - Audio Mastering and Restoration.
http://www.jrpmusic.net