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MIDI By Example (Part 1)

Cabling a MIDI system

MIDI systems - exclusive!


MIDI was designed as an essentially practical solution to the problems of connecting equipment together. So how come it ended up spreading so much confusion amongst those who it was intended to help? In the first of a new series, we get back to practicalities and look at ways in which MIDI can help rather than hinder...

Though it should be a relatively simple system to configure, getting your set-up up and running is often fraught with difficulties - particularly when there don't appear to be enough MIDI sockets to go round.

Figure 1 shows a typical 'daisy chain' method of connecting a sequencer, synth keyboard, a couple of sound modules and a drum machine. The MIDI Out from the synth sends information to the sequencer which it then records. On playback, the recorded data is sent to the synth's MIDI In, a duplicate of which is provided at the MIDI Thru socket and passed on to the first sound module and then to the second. The MIDI Thru from here ensures that the information is received by the last instrument in the chain, the drum machine.

Figure 1: A typical MIDI "Daisy Chain" system


Although the MIDI Thru is designed to duplicate the signal received at the MIDI In, too many synths in the chain can cause this signal to be distorted and the data to be corrupted. A better alternative would be the 'star' set-up shown in Figure 2 using a relatively inexpensive MIDI Thru box. This takes a single MIDI In and duplicates it a number of times so removing the problem of multiple MIDI Thru to MIDI In connections.

Figure 2: Using a MIDI Thru box to create a "Star" system


Using this system, you should, if you wish to play the keyboard, set the Local Control facility to 'off' so that the sequencer controls the sounds. You should also turn the sequencer's 'soft thru' facility on (if it has one) so that you can hear sounds from the modules while you are playing the keyboard.

But what happens if you want to choose between using the pads on the drum machine or the keys on the synth to enter notes in the sequencer? Answer next month...

MIDI Glossary

Manufacturers do it. Music magazines do it. Instruction manuals do it. Happily rattling off MIDI terms in the belief that everyone knows what they're talking about. Many people don't - especially those getting involved in synth and sampling technology for the first time. The result? People never fully exploring the potential of the machines they own, or worse - finding themselves lured away by the simplicity of the guitar and other 'low-tech' instruments.

In an effort to stem this tide, MIDI By Example is including a month-by-month explanation of commonly used words and phrases which will build into a complete glossary of MIDI terms. Where do we start? There's only one place really...

MIDI

In 1982, a small group of manufacturers decided that there needed to be a means by which all their different products could be connected together. As in many other fields, the inability of equipment from one manufacturer to work with that from another was seen as a real disadvantage and a potential limit on people's creativity. What was needed was standardised means of connection between all hi-tech music products so that they could 'communicate' with each other. Thus was born the Musical Instrument Digital Interface - a system quickly adopted by hi-tech equipment manufacturers all over the world.

MIDI comprises two quite distinct parts; the digital information (relating to notes, pitchbend and so on) produced by the machine's internal MIDI circuitry, and the MIDI hardware itself. This culminates in the IN, OUT and THRU sockets (or 'ports') found on MIDI instruments and used to transmit and receive MIDI data.

The degree to which MIDI instruments are compatible with each other depends largely on how much of the standard MIDI specification is implemented on each piece of equipment, and this, of course, relates to the nature of the product itself - synthesiser, sampler, drum machine, processor etc. Obviously there would be no need for an effects processor (for example) to send out information relating to the playing of individual notes.

MIDI has come a long way in ten years and apart from extending the ways in which instruments can communicate with each other, has been adopted as the technology behind a number of creative tools incorporated in both hardware and software-based instruments. For example a computer can be synchronised with, and even remotely control, a tape recorder. MIDI can also be used to produce effects similar to those found on signal processors.

MIDI sockets or ports

MIDI Information is sent out from a MIDI Out port and received at a MIDI In. Thus, in a simple two-instrument set-up, a cable would be connected from the MIDI Out of one instrument to the MIDI In of the other - and vice versa. In more elaborate systems, however, the MIDI Out information from one instrument may need to be sent to two or more instruments. This is where the MIDI Thru port comes in. It carries a replica of the data sent to the MIDI In of an instrument and makes this available (via another MIDI cable) for the next instrument in the line.

Sometimes, when a number of MIDI Thrus are needed (or where none is provided on a particular instrument) a dedicated Thru box is used.

Channels

With different synths and sound modules connected to a MIDI system, there has to be a way to individually 'speak' to each of them. A method similar to television is used; MIDI data is sent on one of 16 possible channels and each synth or sound module is 'tuned in' to recognise the information intended for it. Because of the design of the MIDI system, however, MIDI information from all 16 channels may be sent down the same cables at the same time.

Note numbers

Each note on a keyboard has a different MIDI number associated with it; in order to cover the ten or so octaves used in music, there are 128 of these. The middle C of a standard synth is usually numbered 60; add or subtract one as you go up or down a semitone. On MIDI-equipped instruments, notes are normally referred to by their MIDI note number, however, they may also be referred to by letter/number combinations such as C2 or A#4.

Notes on & off

Hitting a key on a synth generates a MIDI Note On message; releasing it produces a Note Off. Each of these includes data for the MIDI channel, note number and velocity (see under 'Velocity') for that note.

Velocity

Velocity is a measure of how hard a note has been pressed, in the case of a Note On, or how fast the note has been released, in the case of a Note Off. In either case, MIDI determines the value on a scale of 1 to 127. If the velocity is zero, it acts as a Note Off.

Aftertouch

Extra pressure brought to bear on the key of a synth after it has been initially played is called Aftertouch. Most sound modules recognise this and it can be used in various ways to alter the character of a particular sound that is held on - through the introduction of vibrato, for example.

Multitimbral

Meaning, literally, 'many sounding' - a multitimbral synth can be viewed as being a number of independent sound modules in a single box. By setting each module to its own MIDI channel, one multitimbral synth can produce a number of different sounds playing at the same time. This is subject to the maximum number of notes which the instrument allows you to play at any one time - commonly called the 'polyphony'.


Series

Read the next part in this series:
MIDI By Example (Part 2)



Previous Article in this issue

Alesis ADAT Digital Recorder

Next article in this issue

Steinberg Cubase


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

 

Music Technology - Sep 1992

Topic:

MIDI


Series:

MIDI By Example

Part 1 (Viewing) | Part 2 | Part 3 | Part 4 | Part 5 | Part 6 | Part 7 | Part 8


Feature by Vic Lennard

Previous article in this issue:

> Alesis ADAT Digital Recorder...

Next article in this issue:

> Steinberg Cubase


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