Exactly what is MIDI? If you ask just about anyone who owns an electronic musical instrument that was made since 1984 or so, the answer you'll get is likely to be, "It's those plugs on the back." And that answer is right, as far as it goes. But the important thing about MIDI is not the physical connectors or the electronics behind it; the important thing is what it allows you to do. For example, with MIDI you can: * play two instruments from the keyboard of one; or * record your music for playback later; or * synchronize the performance of such a recording with that of an automatic drummer. Still, before you can appreciate all that MIDI does, you really should spend a little time becoming familiar with what it is. What MIDI Is The name "MIDI" stands for "Musical Instrument Digital Interface" -- quite a mouthful. But by breaking this name down into its component parts, you'll find that it's really pretty easy to understand: * "Musical Instrument." You already know what that is. MIDI was designed for use in playing music. Over the years it has found other uses, and has been incorporated into pieces of equipment that are not strictly instruments; but "musical instrument" still describes where it is used most often. (Judging by the first paragraph of this chapter, you might think that a more accurate name might be "Electronic Musical Instrument" But as you'll see later in this book, MIDI can work for all instruments, and voices, too.) * "Digital." This isn't so difficult. It simply means that computers are involved. Since computers work with numbers, and another word for "numbers" is "digits," the adjective "digital" means that somewhere in that MIDI stuff is a computer of some kind. Now, you don't have to know a thing about computers to enjoy the wonders of MIDI. It's like automobiles: You don't have to be a mechanic to drive a car. So don't let this word scare you. * "Interface." Uh-oh -- this one looks imposing. But the meaning is simple: communication. That's all. Now that you understand the parts, let's put them back together: Musical instruments communicating with the help of computers. I told you it was easy. By the way, "MIDI" rhymes more or less with "city." Please don't say "my-dye" unless you want to be branded a "MIDIot." Time for a history lesson: MIDI is a specification that was developed in the early 1980s to allow musical instruments of different brands to "talk" to one another. It was developed jointly by the major manufacturers of electronic musical instruments, and as such, represents a cooperative effort of impressive proportions. Moreover, that cooperation continues, for MIDI is not a formal standard that must be adhered to; rather, it is a specification that is followed voluntarily by the individual manufacturers. The MIDI specification consists of two parts: * The hardware by which MIDI devices are connected. * The "language" that is "spoken" when the devices "talk" to one another. Let's look at these parts one at a time. MIDI Hardware Remember the "plugs" on the back of the instrument? In MIDI jargon these are known as ports. There are three possible kinds: In, Out, and Thru. * IN receives MIDI information from other equipment. * OUT sends MIDI information to other equipment. * THRU provides a duplicate of the information received by IN, to be passed along to other equipment. Not all MIDI equipment has all three ports, and some devices may have more than one of a given type. The MIDI ports of different pieces of equipment are connected by special MIDI cables, which have five pins in each end and plug into the ports themselves. Next, we’ll explain a little about what travels through a MIDI cable from one device to another. The MIDI Language A MIDI cable is something like a telephone line, in that it allows communication between two points. That communication takes the form of MIDI messages. MIDI Rule #1: What travels through the MIDI cable is NOT sound; it's information (data). A typical MIDI instrument will have some kind of audio output, whether it consists of built-in speakers or jacks for connection to external amplification; this audio output is necessary for you to hear the sound that the instrument produces. The MIDI connections are totally separate and different from the audio output. The information in a MIDI message consists of numbers (remember: digital interface). In computer jargon, these numbers are known as bytes, but you can think of them as words. A typical MIDI message consists of one or more words, the meaning of which is specified in the MIDI language. It should be mentioned here that not all MIDI devices understand all MIDI messages. While this might seem like a bad thing, it's really not. It's just that MIDI devices tend to be "specialists," and not all areas of the language apply to all devices. For example, there are some messages that pertain to the synchronization of MIDI recording and playback equipment that do not apply to instruments without those functions. It's like a plumber speaking to a chemist; they both speak the same language, but there are some words that are limited to their respective specialties. The difference is that MIDI devices are "dumb" and totally lacking in curiosity. So when a message comes along that a MIDI device doesn't understand, rather than asking, "What do you mean?" the device will just ignore it and keep going about its own business. This keeps things simple and prevents all kinds of traffic jams in the MIDI cable. MIDI Rule #2: MIDI can't make an instrument do something it wasn't designed to do. So many "problems" with MIDI stem from ignorance of this simple fact. For example, don't expect that connecting a keyboard to a drum machine and holding the keys down will make the drum sounds sustain. A typical MIDI message consists of two or three words (bytes): * First is a status byte, which tells what kind of message it is. A typical example is the Note On message, which is transmitted when a note is played. The status byte says, "This is a Note On message." * Next come one or two data bytes, which provide further information to complete the message. The Note On message has two data bytes: one to tell which note has been played and one to tell how hard it was struck. The three words of a typical Note On message could be translated as: "This is a Note On message." "It's for G above middle C." "Play it medium loud." As you can see, MIDI is a lot more succinct than English, requiring only three words to say what took three sentences to describe here. And it is also fast. A complete MIDI message such as the one just described is transmitted in less than a thousandth of a second. This means not only that receiving instruments will get messages quickly, but also that many messages can be transmitted in a short time. This is especially useful because MIDI can transmit only one message at a time. For example, if you play a three-note chord on a MIDI keyboard, the three Note On messages are actually sent one after another, in rapid succession. Two Categories of Messages MIDI messages are divided into two broad categories: channel messages and system messages. * Channel messages are transmitted and received on a specific MIDI channel, which can be compared to a TV channel: An instrument has to be "tuned" to the correct one or it won't receive what is being transmitted. There are 16 channels available, and each one can carry different messages than the others, over the same MIDI cable. This makes it possible, for example, to play different musical parts at the same time. There are generally two channel settings that apply to a MIDI instrument: the transmit channel is the channel over which an instrument transmits MIDI messages, and the receive channel is the channel over which an instrument will respond to MIDI messages that it receives. * System messages are not restricted to a specific MIDI channel, but rather are transmitted to all equipment that is connected in a MIDI system. This is an efficient way to transmit pertinent information to many instruments at once.
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