Studio Help
All About MIDI
Of all the advances in electronic musical technology the development of the Musical Instrument Digital Interface has to be one of the most important.
Before it became a standard feature of almost every electronic musical instrument produced since the mid 1980's the only way to link equipment together was by using low voltage pulses that triggered similiarily equipped devices and helped keep arpeggiators, drum machines and sequencers in synchronization.
Now, thanks to MIDI technology, it's possible to trigger many compatible instruments, at the same time, from a single source.
In much the same way that computers communicate via Ethernet, synthesizers communicate via MIDI. The information exchanged between two MIDI devices is musical in nature. MIDI information tells a synthesizer, in its most basic mode, when to start and stop playing a specific note. Other information shared includes the volume and modulation of the note, if any. MIDI information can also be more hardware specific. It can tell a synthesizer to change sounds, master volume, modulation devices, and even how to receive information. In more advanced uses, MIDI information can to indicate the starting and stopping points of a song or the metric position within a song.
The closest most people ever care to get to the heart of the MIDI interface are the three 5-pin ports found on the back of every MIDI unit. Labeled IN, OUT and sometimes THRU. These ports control all of the information routing in a MIDI system. The IN port accepts MIDI data, data coming "in" to the unit from an external source. This is the data that controls the sound generators of the synthesizer. The OUT port sends MIDI data "out" to the rest of the MIDI setup. This data results from activity of the synthesizer, such as key presses, patch changes, and so on. The THRU port also sends data out to the MIDI system, but not in the same manner as the OUT port. The data coming from the THRU port is an exact copy of the data received at the synthesizer's IN port. There is no change made to the data from the time it arrives at the IN port to the time is leaves the THRU port (which is a very, VERY small amount of time). MIDI makes use of special five conductor cable to connect the synthesizer ports. Curiously though, only three of the conductors are actually used. Data is carried through the cable on pins 1 and 3, and pin 2 is shielded and connected to common. Pins 4 and 5 remain unused.
Not just any cable will suffice for the exactness of the MIDI system, either. MIDI cable is specially grounded and shielded to ensure efficient data transmission. This means that MIDI cable is a little more expensive than standard 5-conductor cable, but reliable data transmission is absolutely necessary for MIDI. The length of the cable is critical as well, with an absolute maximum cable length of 50 feet because of the method of data transmission through the cable.
Computers and MIDI Computer manufacturers soon realized that the computer would be a fantastic tool for MIDI, since MIDI devices and computers essentially speak the same language, but the MIDI data transmission rate (31.5 kBaud) is different from any computer data rate, so manufacturers had to design a MIDI interface to allow the computer to talk at MIDI's speed. Apple Computer, with the Macintosh and Apple ][ series, and Commodore were the first companies to jump on the MIDI computer bandwagon. Roland designed an interface for the IBM series of compatible computers a few years later, and Atari designed a completely new computer, the ST series, with fully operable MIDI ports built in. Today, there are many different interfaces available for almost all types of computer system, but one of the emerging standards (as of Dec 2000) is USB to MIDI.
In the mid nineties Roland licensed their industry standard General MIDI sound set to Apple, in the form of a software synthesizer, for use within their multi platform QuickTime architecture, making it possible for the playback of MIDI files within a computer without the aid of external hardware, in fact software based synthesis is now capable of emulating classic hardware based synthesizers such as the Prophet 5 and PPG Wave, and looks set to revolutionise the way music is made as computers get more powerful, capable of handling many operations simultaneously.
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