The randomness kind of bothers me. People don't write music randomly, and composition isn't just following some mechanical process and seeing what comes out. This method might get you music that sounds nice, but it can't stand up to music that is actually composed.
If you really want to learn about music, I think it's better to study good music. If you thought adding rhythm had surprising effects, this video will blow your mind: http://www.youtube.com/watch?v=g0ZE38BQmvQ It's an analysis of Mozart in Leonard Bernstein's Norton lectures at Harvard.
The randomness seems to just be in there to illustrate the point about how automatic quantisation can impose structure. The author is just using the example of random notes to show how quantisation can impose structure, even on random notes.
Some artists do use randomness as part of generative music techniques, and it sparks a lot of controversy. In actual fact, randomness is not very useful for composition simply because even if you get something really nice out, you aren't going to get it again. So you either have to record everything, which becomes impractical, or you head into John Cage territory where you embrace the non-reproducibility and it becomes part of the art.
Far more effective to simply wire your studio up in such a complex manner that it behaves chaotically, which leaves you with all the serendipitous, 'surrendering to the machine' type benefits of randomness, but with the added benefit that if you hit rewind and play you will hear the same thing again.
The almighty Autechre, known for their generative music, are quizzed on this in their very interesting and geeky Sound on Sound interview: http://www.soundonsound.com/sos/apr04/articles/autechre.htm (the bit on randomness is halfway down in the "talking about our generation" box.)
Warning: UX people may have a slight breakdown when confronted with the screenshots of their custom software: http://media.soundonsound.com/sos/apr04/images/autechremax2.... (the color spectrum in the bottom right is what fascinates me, talk about indirection...)
"I would hope you put more effort into thinking of a melody and harmony than this, but the point is that rhythm makes a gigantic difference, even if everything else is messy."
I wouldn't have minded some examples, but it bothers me that the entire lesson about rhythm is based on mashing his hands on the keyboard. If you're going to learn about rhythm, it would be useful to know what rhythm is for beyond "it sounds better than no rhythm."
If you aren't Mozart, though, randomness can be a shortcut past writer's block. Sometimes it's a lot easier to rein-in and organize pseudo-randomly generated ideas to make them your own than to allow instincts lead you to the same place over and over and over again.
(Incidentally that Bernstein lecture is great, thanks for linking it)
Very practical, which is great. It is very easy to stay motivated when the tutorial is so focused on producing something that you like.
The only thing that I thought was missing was a discussion about micro and macro pulses in 4/4 versus 3/4 versus 6/8, because it is a simple concept that is easy to teach but offers the student much more variety of options in choosing a time signature. As a music teacher, I usually approach the issue by having students count 4/4 aloud ("1 2 3 4, noting that 1 and 3 are accented slightly) and 3/4 aloud (1 2 3, noting that beat 1 is accented). This teaches not just the structure of the time signatures but helps the student internalize them, which I've found speeds up learning and understanding without sacrificing the student's ability to understand what principles make rhythms work the way they do. (This would have made syncopation a lot easier to teach later in the article-- it can be defined as simply rhythms that don't conform to the usual micro/macro pulse of a time signature, i.e. 1 2 3 4, etc)
Also, one of the easiest ways to grok the time signature concept is to say the signature aloud like it's a fraction. i.e., 4/4 is "four fourths", 6/8 is "sixth eighths" etc. It really is that easy, and this approach combined with the understanding that the lower value gets one beat and there are x of them per measure usually makes time signatures one of the easiest sections of my theory courses.
Still, it's hard to criticize a tutorial that has you producing music so quickly.
Because the micro-pulse of 6/8 is different than 3/4. 3/4 is naturally emphasized as "1 2 3 1 2 3. In contrast, 6/8 is naturally emphasized with a micro pulse of 1 2 3 4 5 6, which produces a strong pulse on 1, a slightly weaker pulse on 4, and a macro pulse of "1 2. (Think 4/4 with triplets). You thus get a much different feeling from 6/8 than 3/4.
OK, my issue was with your statement that time signatures are simply fractions. If that were true than 6/8=3/4. But I understand you were presenting a simplified explanation.
Primarily for reasons of legibility, in my opinion.
Technically, any piece in duple meter could be written in any duple meter and any triple meter piece could be written in triple meter. In fact, you could even write a triple meter piece in duple meter if you are willing to notate everything as a triplet.
Also, as some of the answers below show, part of legibility is in supporting the speed or the feel of the piece.
(Also 2/2 is a fairly common time signature better known as cut-time. Many marches, for example, use this.)
Mostly to indicate tempo and style. A 3/4 measure and a 6/8 measure are the same length, but the 6/8 has twice as many beats at twice the rate. So a composer would use a 6/8 signature for a faster-moving piece with a lot of eighth notes. Similarly, a slow piece would have a 2/2 signature instead of 4/4.
alla breve, cut time: used for marches and fast orchestral music. Frequently occurs in musical theater. Sometimes called "in 2", but may be notated in 4.
That really isn't the case, that is the job of the tempo, a BPM speed set by the composer. The intended difference is purely that 3/4 groups quavers into groups of two, 6/8 into groups of three.
If you really want to learn about music, I think it's better to study good music. If you thought adding rhythm had surprising effects, this video will blow your mind: http://www.youtube.com/watch?v=g0ZE38BQmvQ It's an analysis of Mozart in Leonard Bernstein's Norton lectures at Harvard.