Musical Instrument Digital Interface, or MIDI, is a widely used communications protocol for digital instruments such as the Yamaha DD5. The DD5 is a simple drum machine that can transmit MIDI data but not receive MIDI data. Once you've properly connected this instrument to a MIDI interface on your computer, you can effectively use it to control any software instrument you are able to load, including other drum machines or soundfonts. Given the limited number of sounds included with the DD5, this can be a solid option for a musician on a budget.
Plug one end of the MIDI cable into the "MIDI Out" jack on the DD5, and plug the other end into the "MIDI In" jack on the other MIDI instrument.
Turn both instruments on if they are not on already, and set the MIDI channel on the other MIDI instrument to any free MIDI channel (1 through 16). If you wish the other MIDI instrument to respond to any MIDI channel, set the MIDI channel to "Omni."
Press the "Tempo Up" and "Temp Down" buttons while pressing and holding "Pad Assign" on the DD5 to select the MIDI channel you just assigned on the other MIDI instrument. The default MIDI channel for the DD5 is 1.
Turn the volume up on the other MIDI instrument, then tap a percussion pad with a percussion stick. The other MIDI instrument should now be responding when you play the DD5. If it is not, check your connections and make sure both devices are set to the same MIDI channel.
Press "Tempo Up" and "Tempo Down" simultaneously on the DD5 to set its MIDI channel to 1.