MIDI is an acronym that stands for Musical Instrument Digital Interface. It is a means for instruments to communicate to each other and/or computers. However, not all instruments can do this. They must be "MIDI compatible." However, don't bother checking your tuba, piano, or harmonica, for they are not even electronic, let alone MIDI compatible. What if your instrument is electronic? If it is something built in the 1970's and earlier, you can still kiss the idea of it being MIDI compatible. Otherwise you can look on the back of the instrument and see if there is any connectors (usually two or three) that are a little over a 1/2" in diameter and have five holes arranged something like a "C" laying on its left side. These are what are called "5-pin DIN connectors." Usually you will see them labeled as "MIDI IN", "MIDI OUT", and possibly "MIDI THRU". A few instruments, such as digital horns are likely to have only a MIDI OUT.

    Well MIDI can do many things. One of the most popular things is sequencing. A "sequencer" is any hardware or software that allows you to record music into memory. You can do things with good sequencers that you can't do even with the most expensive multitrack tape recorders, such as transposing without changing tempo and sound quality. Likewise you can change the tempo without affecting the pitch or sound quality. MIDI can allow you to create ensembles using two or more instruments and/or computers. You can download songs off the Internet and play them on a MIDI sequencer that is hooked up to an instrument. With many of today's computers, you can download songs and play them in your computer internally using a "MIDI player". If you don't like the downloaded MIDI song completely, you can edit to your liking with a sequencer. MIDI will allow you to play an instrument that you normally would not know how to play. For example, a MIDI guitar will allow a guitar player to enjoy the sounds of other instruments, such as a piano. It can be a blessing for people who either have only one hand or can only process one hand at a time.

    Unlike your stereo system, MIDI does NOT use sound at all. What it does handle is NOTE DATA, such as what note is turned on or off, how hard a key was hit during recording, when notes are turned on or off. Other data that gets recorded is the usage of a sustain pedal, volume pedal, pitch bend wheel (allows you to slide from one note to another), track volume, stereo panning, reverb depth, amount of vibrato (pitch wavering up and down slightly, but somewhat fast), program change (sound change), and aftertouch (amount of pressure applied to keys while being held down). MIDI has sixteen channels per "bus." A MIDI bus is a network of computers and/or instruments. Better computer systems can handle multiple busses in order to allow a user to have more than 16 channels and better throughput, but this is more for serious professionals. Each MIDI channel can use one or more tracks on a sequencer, but can handle only one instrument at a time. Using additional MIDI channels will allow you to get several instrument sounds simultaneously, provided that your equipment is quote "multi-timbral." This usually refers to MIDI keyboards and digital pianos. At least 80-90 percent of today's MIDI equipment is multi-timbral. Fortunately, this does not seem to be an issue when purchasing a sound card for a computer, for they all appear to be multi-timbral. There are eight basic types of MIDI commands that are used. They are as follows:

    As for the hardware end of it, MIDI is serial in nature. That means just one bit goes through at a time. Thanks to its baud rate of 31,250 bits per second, it seems that things happen all at once. However, even at this baud rate, a MIDI bus can get bogged down if very large amounts of MIDI data is going through in rapid succession. However, this appears to not be a problem unless you are processing 12-14 tracks or more and using pitch bends in two tracks or more at a time or are using a lot of aftertouch, especially poly aftertouch. It uses pins 4 and 5 of the DIN connector. These are the second and forth pins as you are going across the holes of the connector. Note that a MIDI OUT is ALWAYS connected to a MIDI IN on another device. A MIDI THROUGH is like a MIDI OUT except that it is just an extension of the data going into that device.

    Note that you can have only one "controller" in the system. There are three exceptions to this rule. First is if you have a MIDI keyboard and a computer. This keyboard or the computer can act as a controller. When you are recording into the computer, you are using the keyboard as the controller. However, if you are using the computer to play back a MIDI recording, then the computer is now the controller. The second exception is if you have two MIDI keyboards connected to each other, both feeding into each other. This configuration is generally unless; You would be connecting two keyboards so that you can play one and hear both the one that you are playing as well as the one connected to it. The last exception is the one that applies to many serious musicians--the use of MIDI "merging." This is a concept where two or more MIDI OUT’s are merged into one MIDI IN on another device. However, DO NOT attempt to make a homemade MIDI "Y" adapter for this--THIS WILL NOT WORK! It must be done using specific merging hardware, which has two or more MIDI IN’s. Another acceptable route is the use of two or more SEPARATELY ADDRESSABLE MIDI inputs into a computer. In addition to this last possibility, you need to have software that will handle multiple inputs, not just multiple channels.  On the PC platform, multiple inputs are typically merged into one bus.  In order to keep things separate, each keyboard or controller must output on a different channel. You are essentially reading from two MIDI busses simultaneously. With this, you can record using two or more keyboards as a multiple-keyboard organ.