Oberheim DMX Owner's Manual - page 35
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A WORD ABOUT DIGITAL AUDIO
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A WORD ABOUT DIGITAL AUDIO
The DMX is not a Synthesizer. It does not synthesize sound. What
it does is play back sounds from its memory. These sounds are
stored as numbers, inside special integrated circuits called EPROMs
(Erasable Programmable Read Only Memory) which are programmed at the
factory.
Before explaining how digital audio works, let's digress for a
minute and discuss how regular analog audio works:
Sound, as far as your ears are concerned, is caused by very small
but regular changes in atmospheric pressure. The air moves back and
forth, over and over, alternately pushing and pulling on your
eardrums and the rest of your body. When these waves of air occur
between 20 and 20,000 times per second, your brain perceives them as
sound. So anything that makes noise ultimately must disturb the air
in this sort of regular way. Look at the low frequency speaker in
your sound system. If you turn the volume way up (don't damage your
speakers, though!) you will see the speaker (and feel the air near
it) moving in and out, in exactly this sort of regular movement.
So what any analog audio system does, then, is provide a pattern of
regular movement (Oscillation) for the speaker to move in, so that
you feel the air moving in this same pattern so that your brain can
translate all this into sound and you can HEAR! Look at a phono-
graph record very closely and you will see the same repeating
wiggles that are amplified by your amplifier to move your speakers.
Digital audio stores, not the oscillations that move your speakers,
but a series of numbers that represents those oscillations. Take
the groove from that phonograph record and, in your mind, stretch it
out in a straight line and place it on a piece of graph paper. Now
if you went from the left end of the graph to the right, and every
centimeter wrote down a number that represented how far that phono-
graph wiggle moved up and down, you would become a recorder of
digital audio. Now, if you took another piece of graph paper and
plotted all those numbers that you just wrote down, you would do
what a digital audio recorder does to play back.
So what is programmed inside an EPROM in the DMX is a series of
numbers (lots of numbers!) that represents the sound of a snare
drum. Another one has the representation of the sound that a cymbal
makes, and so on, for all of the sounds.