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A MIDI Primer

Multimedia Articles

Written by TParker

Tuesday, 31 August 2004

Article Index
A MIDI Primer
Electronic Musical Information
The MIDI Interface
Using MIDI THRU
The MIDI Channels
Using MIDI Patchbays
MIDI Sequencing and Synchronization
The Anatomy of a MIDI Message
Limitations of MIDI
MIDI 1.0 Specification

Page 3 of 10

The MIDI Interface

Grammatically speaking, using the phrase

"MIDI Interface" is redundant since the last "I" in MIDI stands for Interface. But, for the sake of avoiding bizarre sentences like "Take the

MIDI cable and plug it into your MIDI.", we will continue to say "MIDI Interface". Any decent synthesizer these days comes with a

MIDI Interface built into it... even the ones you can buy at Radio Shack. Most

computers today come with some sort of Sound Card pre-installed that is capable of functioning as a MIDI instrument using

General MIDI or GM. You will need an adaptor cable, though, to plug external MIDI instruments into the sound card so they can be controlled by the

computer and so you can control your

computer's sound-generating capabilities. These adaptor "Y- cable" that plugs into the sound card's joystick port and splits to replicate the joystick port and give you a MIDI IN and OUT port as well. There are also dedicated

MIDI Devices that you can buy for your PC that are considerably more flexible and cost between $50.00 and $500.00, depending on how sophisticated a MIDI interface you need. The most basic, yet more advanced than a sound card-based

MIDI Interface, gives you a MIDI IN, OUT and THRU port or multiple OUTs like a MIDI patch bay - though not as sophisticated. Modern MIDI interfaces generally connect to your

computer via USB. Older serial port.

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MIDI Interface by itself doesn’t do a whole lot for you. You must have some sort of sound-generating device. On the PC, a sound card has a built-in MIDI compatible sound device that can be accessed without any special cabling. Simply load a MIDI file and play it back. There are tons of

MIDI files on the Internet! If your sound card is not one of the new wavetable types, then the sound that you hear will probably be a bit on the thin side. This is because the method in which the sounds are generated is not very sophisticated - relatively speaking, of course. The low-end sound cards use something called

Frequency Modulation Synthesis (FMS), which is a sound producing technology whereby simple waveforms (sine/square/triangular) are combined mathematically to produce complex sound waves. Wavetable Synthesis is actually method of synthesizing sound which uses high quality digitally recorded sounds (

samples) as building blocks to create more complex creations that can then be further modified with digital filters (like compression, reverb, etc.) If you will be using your PC as a sound-generating MIDI instrument (as opposed to just using for the

MIDI Interface), I highly recommend that you invest in a Wavetable Sound Card. They only cost slightly more than a entry-level sound card and your ears, not to mention that base, animal rhythm that exists in us all, will thank you.

Basic MIDI Setup using a single device and a PC-based MIDI sequencer. Earlier, I explained how most sound card MIDI adaptors only have two MIDI ports on them. One of the ports will be a MIDI IN port and the other will be a MIDI OUT port. If you are using only your sound card as a MIDI sound device, then you will never need to hook any MIDI cables to either of the two ports. If you will be using an external MIDI instrument such as a drum machine with your PC, then you will need to take one MIDI cable and plug it into the computer’s MIDI OUT port and take the other end of it and plug that into the external instrument’s MIDI IN port. This allows the PC to send MIDI messages to your external instrument for playback. To record MIDI information from the external instrument to the computer, you will need to plug a MIDI cable into the external instrument’s MIDI OUT port and take the other end and plug it into the PC’s MIDI IN port. When you play notes on the external instrument, the notes will be passed out of the MIDI OUT port and move into the PC’s MIDI IN port. Using a MIDI Sequencer on your PC will allow you to record MIDI information into your PC for playback and editing. This is the most basic MIDI setup. It works very much like water running through pipes.

Let’s review the first two MIDI ports before moving on.

Messages arriving at the MIDI IN port are routed to the instrument’s internal sound-generating hardware.
A synthesizer will respond to messages from it’s MIDI IN port as though they originated on its own keyboard.
All messages that originate from an instrument’s keyboard or other on-board control is transmitted to the MIDI OUT port.

Now let's discuss advanced MIDI setups utilizing the third, and perhaps most useful of the MIDI Interface ports - MIDI THRU. The next section also describes how you can control multiple MIDI devices by assigning them one of the 16 MIDI channels.

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Last Updated ( Wednesday, 24 August 2005 )

Studio Jargon

Square Wave

A geometrical waveform typically generated by an oscillator. It is a special case of pulse wave, where the mark/space ratio is 1:2. It has only the odd numbered (1, 3, 5, 7, etc.) harmonic partials. The amplitude of each harmonic is the reciprocal of its number in the series (i.e. the 3rd. harmonic is a 3rd. the amplitude of the 1st.). It has a buzzy but mellow timbre very similar to that of a clarinet. See also Pulse Wave, Ramp Wave, Sine Wave, Triangle Wave.

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