Disclosed is an interface device to couple a musical instrument to a computing device to allow a user to play a musical instrument in conjunction with a multimedia presentation. The interface device comprises a processor, a D/A converter, and a digital audio interface. The computing device creates a processed digital audio signal of the musical instrument based upon an original digitized audio signal of the musical instrument from the interface device. The D/A converter then converts a mixed digital signal of both the processed digital audio signal of the musical instrument and a digital audio file received from the computing device into a mixed analog audio signal. The processor controls the digital audio interface such that the mixed digital signal is transmitted through the D/A converter, and ultimately through an analog sound device, to the user.