Making Music
  Computer Music Software and Hardware

MIDI Messages

MIDI supports a wide range of musical messages. As well as Note On and Off information there is Pitch Bend and Modulation Wheel data, controllers such as Master Volume, Breath Controller, Sustain and others. Not all MIDI instruments support all MIDI messages although the majority of modern ones support most of them. You can discover what MIDI messages an instrument does support by looking at the MIDI Implementation Chart (MIC) which is usually secreted at the back of the instrument's manual.

General MIDI General MIDI (GM) is not an advanced form of MIDI but simply an agreement between musical instrument manufacturers about which sounds will occupy which preset slots in a GM instrument. For example, Preset 1 is always an acoustic grand piano, 7 is a harpsichord, 41 is a violin and so on. GM was developed so that music song files in a standard MIDI file format could be played on any GM-compatible instrument and sound approximately the same. A GM instrument will also respond to all the usual MIDI messages.

You can see the MIC for Roland's DX-100 here. It's a rather, er, mature instrument now - over 20 years old! The MICs used to look like a game of Noughts & Crosses - and many still do - but it shows exactly which MIDI messages an instrument transmits and recognises. Some manufacturers now use different layouts, partly to include the increasingly-sophisticated MIDI implementation in their equipment. Take a look at some of Roland's MICs here.

Ins and Outs of MIDI

There are three types of MIDI connection - In, Out and Thru. Most instruments have all three but some have just In and Out and some have just one socket, depending on the type of instrument they are.

A MIDI Out socket transmits MIDI data generated by the instrument. That's pretty straight forward. A MIDI In socket is used to receive data from another source. Again, that's pretty obvious. The MIDI Thru socket passes on a copy of data arriving at the MIDI In socket. This is used to 'daisy chain' instruments together so one keyboard or sequencer can control two or more synths.

It's important to realise that the Thru socket is not a second MIDI Out; it does not transmit data generated by the host instrument. (At least usually it doesn't. There are some devices like MIDI Controllers such as the PhatBoy that merge the two data streams, transmitting data arriving at their In socket along with data they generate themselves through their MIDI Out.)

To daisy chain instruments you connect the MIDI Out of the controller keyboard to the MIDI In of the first synth and then connect that one's MIDI Thru to the MIDI In of another synth and so on. In practise, it's far better to use a MIDI Thru box to link instruments. This accepts a MIDI input from a single instrument and may have four, eight or more MIDI Out sockets which transmit copies of the incoming data. It prevents delays and dropouts that can occur when data is passed from instrument to instrument to instrument.

Is MIDI still important?

Most recent music technology developments have been in the field of audio and many musicians now run complete studios consisting solely of a computer, software and a perhaps a MIDI controller keyboard. So does MIDI still have a part to play in such systems?

The answer is invariably Yes. Software instruments such as synths and samplers rely on MIDI data to tell them what notes to play and how to play them.

You might think that if you're only recording audio data you don't need MIDI but many plug-in audio effects such as EQ (equalisation), reverb and chorus can be controlled via MIDI messages. MIDI is also commonly used for mixer automation, making it easier to edit mixes rather than create new ones from scratch. And MIDI is also used to synchronise sequencers, either a software and a hardware sequencer or two sequencers running on the same computer.

MIDI and modern recording

Virtually every modern recording system uses MIDI in some way. If you rely mainly on hardware synths and sound modules or soft synths and sampler, then MIDI is the core of your system. Even if you primarily work with digital audio, you will doubtless have effects that can be more carefully controlled via MIDI. Whichever category you fall into, the more you know about it, the more control and power you'll have over your music.

For more info... The original MIDI spec was developed by the International MIDI Association (IMA). Although they still seem to be in business, their web site has disappeared and the task of curator of the specs has been taken over by the MIDI Manufacturers Association (MMA) who has an excellent site at www.midi.org. Here you can find more MIDI tech specs and information than you'll ever need or want, a list of MIDI messages and lots of other information and links.