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MIDI By Example (Part 2)

Making the switch

Though by no means an essential item, a MIDI Switch box can make life a lot easier when two into one simply will not go...

Anyone who works with a mixer and a tape recorder will have probably found themselves having to splice together a couple of audio leads at some point. The most common occurence is finding yourself with a single input on an amplifier and outputs from two separate instruments. Though strictly speaking, you should use a couple of resistors to construct a basic mixer configuration, it's often not essential to do so. After all, the bodge works, why worry about it? Try the same thing with two MIDI Out cables, however, and you've got problems.

But first of all, let's look at reasons for wanting to connect two MIDI Out cables to a single MIDI In. One possibility would be having to share a sound module with another musician - each of you using your own keyboard. In this situation, because you need simultaneous control over the module, a special MIDI 'Merge' box would be needed - and this will be the subject of a later article.

There are occasions, however, when, though two sets of MIDI Output data may need to be sent, this does not necessarily have to be at the same time. You could, of course, simply unplug one lead and connect the other when the need arises. But a more elegant solution would be to use a simple MIDI Switch box which would allow you, for example, to select between incoming data to a sequencer from two different sources - say, the MIDI note data generated by a synth and that generated by playing the pads of a drum machine.

Figure 1: Using two controllers means you have to recable your MIDI system each time you change between them.

Figure 1 illustrates this situation. As you will see, you can connect either of the MIDI Out cables (represented by the dashed lines) from the drum machine and synthesiser to the MIDI In of the sequencer - but not both at the same time. The rest of the connections ensure that all MIDI information on sequencer playback is received by both the synth and the drum machine.

A MIDI Switch box is a simple affair. It usually comprises a rotary switch which selects one of various inputs and directs the signal to its output. A typical example would be the Philip Rees 2S which has two inputs and one output (£14.95). By wiring this as in Figure 2, life is made much simpler; you simply rotate the switch to determine whether it's the synth or drum machine which is the Master Controller. No more having to reconfigure the wiring.

Figure 2: Using a Switch box removes the problem of recabling your system each time you change your controller.


Following on from last month, we continue our glossary of MIDI terms...

MIDI Controller

Any MIDI device which is being used to transmit MIDI information is generally called a MIDI Controller. Examples such as keyboards and MIDI drum pads are the obvious ones, but don't forget guitar synths and wind instruments - in fact all instruments capable of outputting MIDI data. Incidentally, in MIDI terms, if a keyboard has on-board sounds it is generally referred to as a synthesiser. If, however, it has no sounds of its own, it is termed a Master or Mother keyboard and usually has a superior MIDI specification than a conventional synthesiser.

MIDI Control Changes

MIDI Control Changes are often referred to as MIDI Controllers which, of course, confuses them with the instruments covered by the previous definition. MIDI Control Changes are, in fact, data messages used to alter performance aspects of an instrument or other MIDI-equipped device. For instance, MIDI Control Change 1 refers to MIDI Modulation. Moving the modulation wheel on a synth causes MIDI Control Change data to be sent out from the MIDI Out port to whatever MIDI device is receiving - another synth or perhaps a sequencer.

MIDI Control Change 7 is called MIDI Volume and, as you might expect, is used to vary the level of signal from a MIDI-equipped device. Another common one is 64 - MIDI Sustain Pedal - transmitted every time you put your foot down on a keyboard's sustain pedal.

In all, there are a total of 128 MIDI Control Changes, out of which eight are used for special MIDI Mode messages and various others are, as yet, undefined.

Omni On/Off

You'll see this phrase quite often in a MIDI context. Omni On literally means 'All on' and indicates that a MIDI device will recognise MIDI information received on any of the 16 MIDI channels. Some early synths - Yamaha's DX7 - operated only in this manner. Nowadays, with so many multi-timbral synths being available, Omni Off mode is nearly always the default setting, in order that each voice responds only to the data sent to it via the selected MIDI channel.

MIDI Program (or Patch) Changes

In order to individually select the onboard voices or 'patches' on a synth or sound module, a series of push buttons or increment/decrement controls are included. The action of these controls may be duplicated via MIDI through the use of MIDI Program Change messages.

On a conventional synth, a MIDI Program Change message is sent every time a patch button is pressed - thus, a single button push can be made to call up patches on a variety of different MIDI devices, including signal processors which use Program Changes messages to select between their onboard effects patches. The standard MIDI specification allows for a total of 128 (0-127) Program Changes - though care needs to be exercised as different manufacturers use different numbering systems and conversion may be necessary.


Read the next part in this series:
MIDI By Example (Part 3)

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Gem S2

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Copyrights & Wrongs

Music Technology - Copyright: Music Maker Publications (UK), Future Publishing.


Music Technology - Oct 1992


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MIDI By Example

Part 1 | Part 2 | Part 3 | Part 4 | Part 5 | Part 6 | Part 7 | Part 8

Feature by Vic Lennard

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> Gem S2

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