If you were a MIDI-less electronic keyboard living in the world today — and at this stage I am assuming that in fact this is not the case — you would waken each morning to a damnable existence of appalling isolation and solitude. You would speak, but none would understand you; you would listen, but not a word would make any sense. Indeed, it would be as if you had consumed eight pints of Guinness, or a moderate glass of my Aunt Peg's home made wine.

In the dark and dismal pre-MIDI days such was the outlook for the majority of electronic keyboards. They would often be very fluent and capable within themselves, using their own language, but each product line spoke exclusively in its own electronic tongue and thus could not communicate with others.

This inability to communicate with other current or newly introduced instruments always carried with it the threat of obsolescence. Even then things were moving so quickly that anyone considering the purchase of a keyboard was faced with the knowledge that something better and cheaper was likely to arrive at any time, and that when it did their instrument would immediately become rather redundant. But, in the name of Moog, what piece of mismanagement brought about such a ludicrous situation?

The Original Sin

The whole concept of most electronic keyboards centres largely around the principle of VOLTAGE CONTROL: depressing a key causes a voltage to be generated which is applied to one or more VCOs (voltage controlled oscillators) such that its amplitude determines the pitch of the note produced: a higher note on the keyboard giving rise to a higher voltage and thus a higher pitch. Similarly, many of the other parameters of a synth are controlled by an applied voltage: VCF (filter), VCA (amplifier), and as you slide a slider or turn a knob on the control panel, the chances are you are adjusting a voltage which in turn controls the action of the synth.

When this idea first caught on, every R&D department concerned cancelled all calls, and buried itself in deciding upon the best set of electrical values for these control voltages: Should they be negative or positive? Should an increase of one volt create a one octave change in pitch or is there a better way? And so on and so forth.

Unfortunately, they all came up with slightly different answers, and so trying to control one synth's functions by applying another's control voltages to it just didn't work, and indeed it still doesn't.

The problem was that age-old one of language. One instrument understood a given voltage as one thing whilst another understood it as something else. Interpretation systems were possible, but generally rather limited in their facilities, complicated to implement and thus costly to the point where only the successful pro could afford them.

The industry, then, had long recognised the need for the implementation of some form of universal 'interface' to allow all keyboards to communicate freely. Should you still be confused, an interface is something which allows two or more systems to interact constructively. In other words it allows them to talk to each other. The word can also be used as a verb, so that you could interface system A with system B. If the communication was one way only, it would be a unidirectional interface, and if it were two-way, it would be bi-directional. By virtue of the fact MIDI instruments are able to send and receive information, MIDI is a bi-directional interface.

So anyway, after lengthy consultations with many of the world's major keyboard manufacturers, it was Sequential Circuits who, in close co-operation with Roland, drew up the basic MIDI specification which remains, with certain modifications, today. Now that it is with us, even bears of little brain and limited resources can (theoretically) join together in musical accord MIDI equipped sequencers, drum machines, synthesisers, micro-computers and electronic pianos from any manufacturer, into a single integrated programmable system. It's the Esperanto of the electronic musical instrument world.

MIDI is made possible by the fact that most modern electronic instruments use some form of digital control system, whether or not their actual sound generating system is digital or analogue. In other words, when you depress a key, or move the pitch wheel on a modern synth a series of numbers is generated which determines the action of the synth. In the case of an instrument using voltage controlled systems, as mentioned earlier (VCOs, VCFs, VCAs etc), the necessary control voltages are derived from the numbers generated. A certain set of numbers relates to programme selection, another to pitch information, another to key velocity and so on. By agreeing on a universal numerical code it is possible to have one instrument tell another what to do. All MIDI communications, then, are via a stream of numbers transmitted digitally between the various devices.

Modes

Because the MIDI system has to be suitable for use with the simplest of home keyboards through to the most complex professional instruments, it was designed to work in three 'layers', or 'modes'. Simple instruments work in Mode 1, slightly more complex jobs work in Modes 1 or 3 and the really serious items work in Modes 1, 3 or 4. No doubt those of little faith will be thinking that I've inadvertently omitted Mode 2, but rest assured I haven't; this will be explained a little later; for now just ignore it.

Mode 1: Omni-On Poly

When you connect a number of MIDI instruments together you are providing them with 16 separate channels of communication — just like 16 separate telephone lines. The different modes relate to how intricately an instrument can use these channels. When operating in Mode 1 it simply always transmits and receives n all 16 channels at once. This is termed Omni-On Poly Mode.

Mode 3: Omni-Off Poly

If, on the other hand, you are lucky enough to be using a large and complex system consisting of several instruments, it will be necessary to be able to choose which instrument(s) you talk to during specific parts of your performance. For instance you may be using a DX-7 as your master instrument together with a Jupiter 6 and a Sequential Six-Trak both of which you wish to bring in for swirling string sections, and an Oscar mono synth which you would like to call on for stirring lead lines. Thus the MIDI specification allows any one of the 16 channels to be individually selected at any one time for such exclusive interactions: eg you might talk to the Jupiter and the Six-Trak on Channel 5 and the Oscar on Channel 6. Each preset sound on your DX-7 (or other similar MIDI instrument) can include a MIDI transmit and MIDI receive number that you programmed into it, so that as you call a sound up it automatically selects the correct channel for the other instrument(s) that you wish to talk to, or indeed turns the MIDI communication off should you only wish to play the DX in isolation. This kind of operation where individual instruments can be assigned to different channels takes place in Mode 3 or Omni-Off Poly Mode. Most instruments with any claim to being professional will be able to handle Modes 1 and 3.

Mode 4: Omni-Off Mono

This is a more specialist mode found on relatively few synths, and allows each voice ('voice' as in 'six-voice polyphonic') of an instrument to be addressed on a separate channel. The benefits of this can be clearly seen in the case of a 'multi-timbral' instrument such as the Sequential Multi-Trak (see entry in £1500 to £2500 section for more explanation) whereby a single instrument can be treated as several individual instruments, each with a different sound.

Mode 2: Omni-On Mono

Originally due to a miscommunication, Yamaha came up with this mode where all channels are transmitted/received on simultaneously, but you can play in mono. Few synths can be configured for this mode.

A MIDI instrument shall be recognised by the two or more 5-pin DIN sockets (as on your hi-fi) worn about its rear panel, marked 'MIDI IN' and MIDI OUT'. These sockets or 'PORTS' are its ears and mouth that allow the two-way communication of which I speak. Certain more sophisticated models will have a third port marked 'MIDI THRU' (American spelling) which allows the connection of more than one instrument in a chain configuration, with the first one in the line being the master, from which the rest will generally be controlled.

So now that they are blessed with the power of communication, what is it that these instruments find to talk about? One of the simplest applications of interfacing several instruments is to allow them all to be played from one keyboard. In this way you can have the power of two or more synths playing the same line without the inherent physical difficulties of only having one pair of hands, and only being able to be in one place at a time. The detail to which one instrument can talk to another depends on each one's general abilities and the comprehensiveness of their MIDI facilities. For instance some instruments will be able to transmit keyboard touch information, but unless the receiving instrument is touch sensitive it won't be able to respond accordingly. Also in matters of performance controls only the pitch bend wheel has been assigned a definite code, and so there may be (and indeed are) mismatches between instruments from different manufacturers, and certain parameters may or may not be accessible through MIDI. When you buy an instrument you would be well advised to check with the retailer that it is capable of doing what you require of it.

A MIDI drum machine can also be played or programmed from a keyboard, where each of the drum voices corresponds to a given key or keys on the keyboard. Conversely, a drum machine can be used as a basic sequencer to play a keyboard in a very simple fashion. See last month's IM&RW for a round up of drum machines, MIDI and otherwise.

MIDI Sequencers

A sequencer provides a means of recording a performance and can be seen in many ways as a solid-state version of tape recording. There are basically two ways of recording; step time and real time. With real time you simply drop the sequencer into record and play the piece to be recorded. The beauty of a good quality sequencer is that it will correct for your timing inaccuracies and allow minuscule corrections to be made to individual notes without affecting the rest of the performance. Step time programming is altogether more laborious but comes in handy for those who enjoy only limited dexterity. In this case you separately select the time and pitch values of the note to be entered, and then enter them without any musical performance. Having thus entered each note in relative isolation, the sequencer will then play the composition back. A good sequencer also offers a number of other facilities which make the life of a composer simpler, such as 'looping' whereby you play a musical phrase once and then ask the sequencer to repeat a given number of times. You can also record at a very slow speed to ensure accuracy, and then play it back faster thereby appearing to be a flash git when you really only used two fingers.

The tape analogy goes further to the extent that multitrack sequencers can be treated very much like multitrack tape recorders in that you can build up an arrangement, track by track, and then have the sequencer play the whole thing back, and you still maintain all the editing control as mentioned above. Using a MIDI system for much of your multitrack work means that you don't need a lot of tracks on tape for recording songs — in fact only vocals and non-MIDI instruments need more than a stereo pair. Also, if you're recording in a commercial studio, a sequencer allows you to perfect your performance before the red light comes on, so possibly saving you a lot of money and maybe also a little face. In addition there are similar applications for live performances, where computer controlled sequences can be used to save hands.

As with different MIDI keyboards facilities will differ from model to model, some units will recognised touch information and performance controls whilst others won't. Also the amount of memory will vary greatly, the Yamaha QX1 for instance will be able to store well over half-an-hour of complex multitrack music, whilst its little brother, the QX-7 is limited to a few minutes. You pays your money, etc.

Computers

One of the really exciting possibilities opened up by MIDI is that of being able to use a home computer as a sequencer. There is an ever-growing range of software packages available for MIDI application. This option won't necessarily be cheaper than buying a dedicated sequencer, but if you already own a computer, or fancy getting one, it's an excellent option and can offer some extremely sophisticated facilities.

MIDI Ancillaries

Inconvenient though it is, all those instruments built before the arrival of MIDI remain with their own forms of control such as CVs (control voltages) and gate pulses and in the case of the older Roland products the DCB system. Hence there are a number of boxes which serve to interface such relics with the glorious MIDI system:

CV/Gate to MIDI

Digi Atom 4800 — £400
Roland OP-8M — £550
Sycologic AMI — £458

MIDI to CV/Gate

Roland MPU-101 — £275
RMS-7HCGX — £219

MIDI to DCB

Roland MD-8 — £300

Channel Filters

In addition there are other 'filter' boxes, such as the Roland MPU-103 at £225, which allow Mode 1 only keyboards to select specific channels, or 'parallel' boxes that allow a single MIDI OUT port to quickly and easily feed a number of other devices without delays:

Time Code Applications

It is possible to use SMPTE and EBU time code from tape to control MIDI functions via a suitable interface such as one of the following: