Whilst it started life as a musical techno-link MIDI has beenstretched to the control of sound and lighting apparatus and multimedia. Two companies, Yamaha and Sequential Circuits, developed a standard specification in the early 1980s for communication betweenelectronic musical instruments which they called MIDI (Musical Instrument Digital Interface). It was successfully adhered to by manufacturers without change - something which can rarely be said of computing "standards".
MIDI comprises 16 channels of data distributed via a cable with standard audio 5 pin DIN plugs at either end (the same as those used to connect hifi components). The data is transmitted down the cable in serial format which can include note information, controller data to add expression and system exclusive data to allow detailed editing of particular synthesizer parameters since the MIDI specification allows each instrument manufacturer to build in their own specific/peculiar commands etc. To synchronise different instruments a clock signal is also sent.
Many different synthesizers can be connected together in a daisy chain and all controlled from the one instrument. Since electronic data is sent a computer can be used to edit instruments for a particular synthesizer (cello, harp, flute, trumpet etc) or control which synthesizer in the chain is to play. Many software packages exist for these and other functions. Instead of a synthesizer other electronic instruments such as drum machines and sound samplers can be used.
With the expansion of MIDI to control such things as tape recorders and lighting systems the standard was seen to be stretched to its limits and so new protocols started to be considered.
One of these protocols has been developed by the University of California, Berkeley with Zeta Music. They have called their system ZIPI and designed it to be future proof by giving it an unlimited bandwidth (EXPLAIN). This increases the maximum data transfer rate and brings more possibilities.
ZIPI works using addresses instead of 16 channels each address being generated by instrument family, instrument and note number. This means that you can direct data to a particular synthesizer (eg number 10 inthe chain) and tell it to play note A on, say, the violin. By using addresses in this way it does not simply replace MIDI since it has to be remembered that many old classic synthesizers cannot be easily or cheaply upgraded. It uses just one socket rather than MIDI's in, out and thru simplifying connection.
As it is possible to edit MIDI information (eg create new instruments or variations of existing ones) the information can be saved as a file. MIDI itself does not dictate which sounds are to be used. So when someone else uses your file problems can occur with instrument assignments eg. a brass piece created on your set-up might play on your friend's with snare drums and bagpipes. When the MIDI files are only used by one person this is not a problem, but when they are distributed to others a standard needs to be adopted to ensure consistent results. With the growth of multimedia and operating systems such as Windows it has become possible to use sound files such as MIDI files to enhance applications. A common standard is required for this.
General MIDI was developed in the early 1990s based on a new breed of (multi-timbral) synthesizers, the first of which was the Roland MT32 released in 1987. Up until then synthesizers were only capable of generating one or two sounds at once. But with the advent of digital synthesizers cheap, keyboardless modules appeared capable of producing at least 8 individual parts. With General MIDI 128 instruments are arranged in a standard order (eg 1 = acoustic grand piano). And hand in hand with the specification for General MIDI came standard MIDI files. There are now a large number of MIDI files around from Mahler's Eighth Symphony to the latest pop song.
General MIDI devices must be capable of playing 24 notes simultaneously (24 note polyphony) including drums over 16 independent parts.
Some computers, such as the BBC Micro, had synthesizers specially developed for them. One such was the Music 500 which appeared in 1984 followed by an improved version (the Music 5000) in 1985 both made by Hybrid Technology. This was merely a box that plugged into the computer which generated sounds from the information provided by the computer. The sound was heard by connecting the unit to an amplifier and speakers. This was actually only an analogue synthesizer, although sound output was stereo. Software was provided which enabled the user to input notes as text or directly onto the stave. A piano style keyboard was later produced which plugged into the computer. This enabled music to be played directly rather than having to be built up and played back. Either the computer or additional keyboard could be used to input notes to build up a piece of music. A MIDI interface was also produced enabling control of up to 32 instruments or devices. The M5000 provided 8 voices over 16 channels, although this could be doubled with an expander.
Discrete MIDI interfaces have been produced for most home computers at some time or another. Some projects have appeared in electronics magazines for the home constructor. Some machines, such as the Atari ST, had a MIDI interface built in during manufacture.
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