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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

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Using MIDI Patchbays

MIDI Patch Bay is a device that allows dyna mic control over your MIDI devices. Models come with up to 34 MIDI IN/OUT ports (sometimes even more, if you can find one) and each input port can have the output of any other port in the patchbay mapped to it. This allows for complex, multiple MIDI setups available to you at the push of a button. If you have multiple

MIDI Sequencers or a Dual

MIDI Interface for your

computer, using a patchbay would allow you to dyna mically control up to 32 MIDI instruments using two groups of 16 MIDI channels. The most common MIDI patchbays, however, have 8 INs and 8 OUTs and cost around $200.

Let us say that in your studio setup you have a master keyboard that is multi-timbral, another multi-timbral MIDI device, Example of a MIDI recording setup using a MIDI Patchbay or MIDI router. like a MIDI drum machine, and a digital effects unit (can you say reverb?) that can change presets using MIDI. Remembering that each multi-timbral device can respond to each MIDI channel simultaneously and assign a different sound to each channel, you can see how quickly you could eat up 16 MIDI channels with even such a small setup - unless you were doing a bunch of sound layers. With a MIDI Patchbay, you would plug your MIDI sequencer into the IN and OUT of the patchbay’s first group (remember: MIDI OUT can only plug into MIDI IN), plug each of the other MIDI devices into the patchbay in a like fashion, and you can then assign the sequencer’s MIDI output (IN on the patchbay) to be broadcast to each of the patchbay's MIDI OUTs. Another interesting aspect of a MIDI patchbay is the ability to isolate instruments from the sequencer. Not all devices attached to the patchbay have to respond to the sequencer, they can be configured to respond only to a specific device patched into the patchbay (such as the master keyboard or some other alternative controller). Any MIDI IN or OUT on the patchbay can be configured to respond to accept or send data to any of the other ports simultaneously.

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This type of assignability allows you to do things like direct-to-synth patch dumps or the transmission of device exclusive data that would not be as easily accomplished using a MIDI daisy chain setup. Remember, in a MIDI daisy chain setup, those devices that are being controlled from the master

keyboard's THRU port will only be able to receive MIDI data. You can send patch changes, but you would not be able to dump data directly from a device in the chain (other than the master

keyboard), because the device's MIDI OUT port is not being used. MIDI patchbays remove the one-way communications limitation that plagues daisy-chainers. (Sounds kind of obscene, doesn't it?)

A low-cost alternative to a MIDI Patch Bay is something called a THRU BOX. A THRU BOX is a small device that has a single MIDI IN that is copied to three (3) or more MIDI THRU ports. The duplicated input can be sent to as many separate MIDI devices as your THRU BOX has ports. As we just discussed concerning using THRU-based setups, much of the MIDI traffic in such an environment is "one way", limiting the flexibility/accessibility of the devices. A MIDI Patch Bay is the best way to go if your budget allows. Now, how do you make music? It can be a pain in the neck sometimes to get everything working together in your MIDI "network". But, once you have the jungle of cables sorted out - you'll be ready to make some music. So, let's read about MIDI Sequencing and Synchronization in the next section.

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Last Updated ( Wednesday, 24 August 2005 )

Studio Jargon

Pulse Wave

A family of geometrical waveforms typically generated by an oscillator. They are all rectangular in shape, i.e. the only angle which occurs is 90° between immediate, vertical transitions and horizontal "high" or "low" levels, but they have any possible mark/space ratio. Square wave is a special case of pulse wave where the mark/space ratio is 1:2. The harmonic partials present are determined by the mark/space ratio such that the harmonics which are multiples of the rightmost number in the ratio will be absent. Thus a pulse wave with a mark/space ratio of 1:3 will not have the 3rd., 6th. or 9th. etc. harmonics. Other harmonics will be present at varying amplitudes depending on their proximity to the "dead" or absent harmonics. When the ratio becomes very large i.e. the pulse becomes very narrow, the timbre becomes correspondingly thin and nasal, rather like an oboe or harpsichord. See also Ramp Wave, Sine Wave, Square Wave, Triangle Wave.

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