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Quick Guide To MIDI

What is MIDI, how does it work, and does it still have a place in today's music environment? We answer these questions and more...

MIDI stands for Musical Instrument Digital Interface. It's a communications protocol or set of instructions that enables electronic instruments such as synthesisers, samplers and computers to 'talk' to each other. It was the first widely adopted standard for the transmission of music information and it's found on virtually every kind of electronic instrument today from hardware synths to sound cards.

Where MIDI came from

To understand exactly what it is, what it does and why it was developed, we need to go back to pre-MIDI days circa 1982. At that time, synthesisers were expensive beasts and sounds were created by twiddling vast arrays of knobs and sliders. Most could only store one sound at a time - no presets here - and they were primarily analogue in nature. That means sounds were produced with analogue circuits such as oscillators, filters, LFOs (Low Frequency Oscillators) envelope generators (for shaping and controlling volume) and so on. All good techy fare!

Voltages were used to control these modules and shape the sounds. In fact, you'll still hear the term Control Voltage (CV) used in connection with modern synths (although in practice they generally use digital circuitry to simulate CV control). The system worked fine but there were several problems. For example, each synth manufacturer used a different CV system so it was difficult to use one company's synth with another company's sequencer. This effectively tied musicians into using products from just one company.

Fast forward to 1982 when some forward-thinking developers and companies got together to discuss a universal standard for the transmission of musical information. It was originally known as UMI (Universal Musical Interface) but a year later after several revisions it became known as MIDI. By 1986 hardly an electronic instrument appeared without MIDI sockets.

How MIDI works

The main thing to remember about MIDI is that it handles music 'data' or instructions. It does not transmit 'sound' at all. For example, when you press a key on a MIDI keyboard, this generates a Note On message. When you release it, a Note Off message is generated. If this is sent to another synth it will play the note exactly as if you were playing it from its own keyboard. 

Note messages also carry with them Velocity information, which is how hard the key was pressed, and this is normally used to control volume. However, the actual 'sound' selected on the controlling keyboard is not transmitted. So, for example, if the controller was set to a piano sound and the receiving instrument set to a flute then it would play a flute sound.

You can change the preset number of the receiving instrument by sending a Program Change message but, again, this simply selects a different preset on the receiving instrument, it does not somehow magically send the 'sound' of the controlling instrument to the receiving one. If you think about it for a moment you'll realise how impossible this is as it would require the second instrument to have exactly the same sound generation circuitry as the first but it's a common area of confusion for beginners.

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