About MIDIs

Note: This information is very old. It was originally written back in '97, and needles to say things in the world of computers have changed a lot. So take what's written with a grain of salt when I'm talking about hardware.

What is a MIDI? What's so good about MIDIs? Why not just use Wave files or something else? These are a few of the questions I've been asked about MIDI, and I've found that many people don't really know what MIDI is. I hope to answer some of these questions here, including why I like MIDIs. I've also set up a demonstration of how MIDIs sound different on different computers.

I like MIDIs for a few reasons. Mostly they are just so cool and sound like you are listening to a concert. It is also active participation, because you can compose your own songs using any instruments, even if your playing skills are not the best. I like music a lot and with MIDI there is only the music, no lyrics. This is nice because, while I like songs with vocals too, I some times prefer to just compose or listen to the music. The files are also very, very small in size and take almost no computer power to play, which makes them great for playing in the background of your computer or web page. Also, usually but not always, MIDIs are handled independently of the portion of the sound card that plays all other sounds. This means you can still hear other attention getting sounds while you play a MIDI file, which you can't hear with a Wave or other format playing. These are a few of the reasons I like them.

What is MIDI? MIDI stands for "Musical Instrument Digital Interface". It is not really a computer file format but rather it is a protocol used by electronic musical instrument, to communicate with and control each other. In the case of computers the sounds card is the musical instrument like a synthesizer. In fact that is what the sound card is, a synthesizer. However, this goes far beyond the scope of this page, so for the purpose of this page we will think of it simply as a file format. (If you would like to learn more concerning MIDI as it pertains to musical instruments you can check out the MMA Home Page.)

A MIDI file is very different from other typical audio file formats like a Wave file (which is Pulse Code Modulation [PCM]), or RA (Real Audio) or Mpeg files (which are both just compressed PCM files). There is a big difference both in what is stored and how it is read. In Wave and the other audio formats, a digital representation of the actual sound waves of the source are digitally recorded. Just like on a CD recording, the sound waves are digitized and stored on the CD. In contrast MIDI just contains the information about which notes are to be played, and by which instrument. Another way to think of it is that MIDI is like sheet music, it contains all the information/notes needed to play a song on the proper instrument(s). The advantage to MIDI is that it takes much less space to record just the notes instead of all the digitally represented sound waves. That is why a MIDI several minutes long is still smaller than a Wave file only a few seconds long.

Now the big disadvantage to MIDI is that since it is only the musical notes that are saved, the MIDI will sound very different on different computers/sound cards. You can think of it again like sheet music (MIDI) and a CD (Wave, RA, or Mpeg). If you take a CD, and put it into a player it will sound, more or less, the same no matter where you play it or in which player you play it on. On the other hand if you have a song on sheet music, you will also need someone to perform the music. If you have a good professional group, they can play the song and it will sound great. If you get a lower quality group they may not have all the instruments or even the right instruments, and it may not even sound like the same song. This is why there is a big difference between the way a MIDI sounds from one computer to another.

There are three basic methods that sound cards use to play MIDIs. One is called FM synthesis, and another is called wavetable synthesis. Sadly most computers come with standard sound cards that use FM synthesis. Often many people don't even realize how bad it really sounds, since they have never had anything else to compare it to. The better sound cards use wavetable synthesis which is worlds better in quality. However, even among the same types of synthesis the quality will vary.

FM synthesis is the most common method used to play MIDI's and is what is found on the standard sound cards found in most computers, like Sound Blaster 16 for example. It works by using simple mathematical properties of sine waves to simulate what the real instrument should sound like. In fact all sound cards can use this method, even those with wavetable synthesis. FM synthesis is the equivalent of an amateur band using the wrong instruments, like kazoos. It sounds like computer sounds, beeps and tones, rather than like real instruments.

Wavetable synthesis is the second method, and is much, much better than FM synthesis. Wavetable synthesis works by recording a sound sample of one note (or occasionally a few different notes) from the actual instrument, which is stored (in PCM) in the wavetable's memory. The wavetable then takes that one note and modifies it to give the full range of the instrument's sound. Since you are using the actual sound from that instrument, it sounds much, much better. This is in fact how most all professional synthesizers work.

Here is an example of the difference in the sound quality between the two methods. If you where listening to a sound reproduced by FM synthesis you might ask, "Was that suppose to be a violin?" While with that same sound reproduced by wavetable synthesis you might ask, "Was that a Stradivarius violin?". A good wavetable synthesizer will sound like a CD recording of a performance.

Recently a third method has become available now that computer power has risen high enough to support it. Traditionally with wavetable synthesis so much processing power is needed that separate special hardware is used, the wavetable. But now with increased CPU speeds it is possible to write programs that use this extra power to do with software what a wavetable does with hardware. The principle is the same, and the sound quality from these new programs is very good, rivaling that of some wavetables. However, they demand a lot of computer power and a lot of the CPU's resources to run, especially if you want to run them in the background. This means they slow down a computer more than a wavetable, and you need a faster CPU to take full advantage of them.

I hoped that helped you understand MIDIs a little.  If you would like to hear the difference between these various methods, or hear how your sound card compares, I have set up a demonstration.