This process of a computer sending back out the MIDI messages that it just received is called echoing. You choose what instrument the messages come back to by using the software. When you play your controller, the MIDI messages go to the interface, then into your computer, and then back to the interface and to a specific MIDI instrument that’s connected to the interface. You can use a controller to record yourself playing in real time.

You can also get MIDI converter modules that turn guitars, drums, and other instruments into controllers. The instrument that you connect to the MIDI IN of your interface is called a controller, and typically has a piano-style keyboard for sending note on/off messages, pitch and modulation wheels, and perhaps some sliders on it for sending other MIDI messages to the interface.

You also connect a MIDI cable from the MIDI OUT on one of your MIDI instruments to the MIDI IN on your MIDI interface. You connect a MIDI cable from one of your MIDI interface’s MIDI OUTs to a MIDI IN on an instrument.

MIDI instruments have inputs and outputs labeled MIDI IN and MIDI OUT. Most inexpensive sound cards have internal synthesizers that can make at least 128 different sounds (if you’re using a synthesizer that’s built into your sound card, you don’t have to connect that to the sound card, since the connections are internal to the sound card). MIDI instruments can be stand-alone synthesizers or can be built into your sound card. A MIDI interface contains inputs and outputs, labeled MIDI IN and MIDI OUT, which you connect MIDI cables to so you can send MIDI messages to and from MIDI instruments. That’s how MIDI software plays MIDI instruments. Your computer sends MIDI messages to your MIDI interface, which then sends them on to your MIDI instruments. You need some way to get MIDI messages into and out of your computer, so a MIDI system needs a piece of hardware called a MIDI interface, which can be a stand-alone module connected to your computer’s parallel, serial, or USB port an internal module installed in a slot inside your computer or can be part of your sound card.

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