Harmonics question

[R.G. Keen]

>I understand that a square wave is made up of sine waves, but what are the
>exact frequencies that the harmonics oscillate at?  For example, if you
>have a square wave at 130Hz are all the harmonics octaves up and down from it?

The harmonics (called "partials" in music theory) are integer multiples of 
the fundamental frequency. Square waves are made up of only the odd multiples
of the fundamental. So a 130HZ square wave has a fundamental of 
130Hz, the third harmonic at 390Hz, the fifth at 650, the seventh... etc.

If you had not a square wave, but a triangle or sawtooth, it would also have the
even harmonics in it, so it would have 130, 260, 390, 520, 650, ...

The harmonics each have different, usually decreasing, amplitudes.

Note that every waveform which recurs in the same shape over and over is made up of
the fundamental and its harmonics. Non periodic waveforms may have other non
harmonically related frequencies in there.