Tech Tip:What is MIDI?: Dr. Digital Explains




How MIDI Works/How It Works and What You Need To Know
It wasn't so long ago that the term MIDI was used only in reference to a handful of keyboards and sound modules. It seemed that no one besides studio wizards and engineering geeks needed to know what it was or how to use it. But these days, MIDI is a key feature on all sorts of musical equipment, from mixers and effects to guitars and drums.


So what is MIDI, and why is it such a popular and important part of making music today?


MIDI, short for "Musical Instrument Digital Interface," was created almost twenty years ago so that keyboards by different manufacturers could communicate with one another. Initially it was used to help create layered keyboard parts and to store and edit patches (the locations where sounds are stored) between devices. As the technology developed, MIDI proved to be an excellent and efficient means of recording and playing back musical performances. This last aspect has become the most prominent use for MIDI in the last fifteen years or so.


What MIDI Does
Remembering what "MIDI" stands for makes it easier to understand what it does. Musical Instrument Digital Interface: It converts what you create on your Musical Instrument into a Digital format so that you can Interface with other gear. The MIDI process converts any played performance information -- pressing a key on a keyboard, turning a knob on a synthesizer, bending a note -- into digital information. That information is then digitally transmitted over a standard 5-pin cable to any MIDI device that has a MIDI In, MIDI Out or MIDI Thru jack.


Here's where you say, "Wait a second. Digital information? So using MIDI is the same as recording guitars or vocals on my computer?" No! See, MIDI information isn't sound (audio) on its own -- it tells an instrument what notes to play and which sounds to make. You always need to have some sort of MIDI sound module as a sound source to play back MIDI information. You can't actually hear MIDI on its own as you can with digital audio.


The Advantages
Because MIDI is information about sound rather than sound itself, a MIDI user has the advantage of being able to alter the information before being played back by a MIDI module. When using MIDI with a sequencer, you can record, modify or edit your performances far beyond what you're able to do with other means of recording. For instance, if you were to record a piano part as audio and you play a wrong note within a chord, you would have to punch-in a new chord in order to fix it. When recording a MIDI part, you can view the played notes, make whatever adjustments you like, and then choose which notes you want to keep and which ones you don't. That's because you're dealing with flexible digital information. It's like changing the text in a word processor before printing it out.


With MIDI you can also change the timing of individual notes by quantizing, alter the dynamics of the performance by changing velocity and adjust many other aspects of a performance. Best of all, you can choose or alter the sounds right up until the mixdown process. If you play a part using a harpsichord sound and then decide you'd rather hear it on an organ, a clavinet, or any other sound imaginable, the change is just a few clicks away.


Current MIDI implementation allows for 16 separate "channels" of MIDI to be transmitted over a single MIDI cable, which generally means that 16 different sounds or parts can be played back at the same time from a single MIDI sound module, if the module can handle it. (Most MIDI data takes the form of a number between 0 and 127 translated into hexadecimal form using the numbers 0 to 9 and the letters A to F. But let's save that for another article.) You can see that you wouldn't need many sound modules at all to have a veritable MIDI orchestra at your command.


MIDI Everywhere
MIDI is being used more widely serving more varied purposes than ever before. Standard MIDI files can be found on Web sites, multimedia CD-ROM' s, and even stranger places like karaoke machines. These files are original compositions or popular recordings that have been converted into MIDI and set up to use a standardized playback format called General MIDI (GM), which allows different instruments to play back from a computer's built-in soundcard or GM synthesizer. MIDI files using the General MIDI standard ensure that the instrumentation (piano, strings, etc.) remains the same when the files are played back, no matter what GM instrument or soundcard is used as a sound source.


No doubt about it, MIDI has had an enormous impact on the recording industry. It's used in the smallest home setups and in the world's most sophisticated studios. At this point, it is one of the easiest and most versatile means of creating musical arrangements.


Keep an eye on this section to learn some of the ways you can use MIDI to alter your performances, and how MIDI can make your life a lot easier.