Re: Additive Synthesis

Hi.

First of all, why do you want to know strict definitions of what is and
isn't additive synthesis? If you're going to write an essay on the
subject, then it would make sense. If you just want to make some sounds
this way, though, I wouldn't worry about what the technical term happens
to be for what you're doing. As various people on this thread have
pointed out, there's a fine line between when one method of synthesis is
used and when another one is used. Often, a lot of fun can be had in the
combinations.

From what I understand, the gist is that you can make musically pleasant
sounds by creating many different sine waves. As long as every sine wave
prsent is a multiple of the slowest one (they are called harmonics, and
the slowest one is called the fundamental harmonic), the sound you get as
a result will sound very musical.

As far as I know, electric organs make waveforms that are very similar to
sine waves by spinning metal discs, and these waveforms are all multiples
of the lowest one (with an extra one an octave down from the fundamental
harmonic for good measure), so yes, that would make an electric organ an
additive synthesiser as much as a Mellotron is a sampler. :) They're not
up there with cutting edge electronic synthesisers, but they use the same
process to good effect in their own right.

Where it gets interesting is if you change the volume of all the different
harmonics over time. This is exactly the same as pushing and pulling the
drawbars while playing an organ. The more sine waves you have, the
clearer the sound can be, and there's no limit to how many you can add
(although as humans can't hear anything louder than about 20,000Hz, a few
thousand would be more than enough). You obviously can't change the
volume of all of these sine waves by hand, but you can program a computer
to do it automatically.

For example, if you make the second sine wave half the volume of the
fundamental one, the third a third of the volume, the fourth a quarter,
and so on, the result is a sawtooth waveform. The more sine waves you
add, the closer the resemblance gets, but it's amazing how close it gets
with only a handful. Adding more makes the sound brighter as you're
adding the higher frequencies.

If you only include the first, third, fifth, seventh and so on sine waves,
removing every even numbered one, you get a square wave instead.

So if you program a computer to keep all of the odd numbered harmonics
present and fade in and out the even numbered ones, you can make a
waveform that slowly morphs between a sawtooth and square wave.

I could be wrong about the terminology, but I managed to write a quick
program a while back that output a slowly evolving waveform that morphed
between a sawtooth and square shape, so at least some of what I've said
should be accurate, I hope!

If you want to use something other than a sine wave as a starting point, I
don't know whether it still counts as additive synthesis or not, but by
all means try it - you may discover something new for all I know. At the
end of the day, if you're trying to make new and interesting sounds, try
not to box yourself into the mindset of using one particular method.
Feel free to combine different methods together, just as you're combining
science and art.

Does that help at all? I hope this post wasn't too redundant.

Zoe.
.

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