Bruce Olsen wrote:
>Also it came as a surprise to me to find the Basics sound command gives
>square waves at the speaker (ABC2WIN and my ABZ player). Norbeck's
>AbcMus I haven't examined much, but my trials on A=440 lead to an audio
>signal out as a three part sawtooth for each cycle. The ear doesn't seem
>to much care how close to a sine wave it is, as far as calling it
>'music' goes.
In fact, using a pure sine wave to make music is in some ways a bad idea.
If you play a sine wave from a good tone generator in a normal room, and
then listen carefully to it as you move around the room you will notice
all sorts of strange acoustic effects. The sound appears to come from
different directions in different places, It gets unexpectedly louder
in some places, and sometimes disappears altogether in one ear, although
you can still hear it with the other. If you try to tune a real
musical instrument to it you will notice that it is much more difficult
than you expect.
The reason for this is that the sound reflects from the walls of the
room and forms a pattern of standing waves. Sound from a real instrument
will do that too, but because real instrument sounds contain a mixture
of harmonics the different frequencies fill in the antinodes of each
others standing wave pattern, covering up the effect.
The instrument which produces the nearest to a pure sine wave is the
lower notes of the flute, although even here there is some sixth harmonic,
and a little random noise. It is much more difficult to tune your
guitar to a flute than to a piano. A sawtooth waveform is in some sense
a much more musical sound than a sine wave. After all, the basic
waveform produced by a violin string is a sawtooth, because in each cycle,
the bow pulls the string slowly to one side, then it snaps back into place.
Of course the sound that you hear is considerably more complex because
it is coloured by the wood and air resonances of the body.
Phil Taylor
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