Harmonics question

Magnus Danielson magnus at analogue.org
Wed May 20 22:59:26 CEST 1998


>>>>> "S" == Stopp,Gene  <gene.stopp at telematics.com> writes:

Hi Gene!

 S> Right - subharmonics are all over the place in the real world.
 S> Analog synthesis is only a crude approximation of real world mechanics -
 S> it's functions are "analogies" of actual movements, hence the name. For
 S> example, these waveforms we talk about are just different ways of
 S> "plucking" an imaginary string with zero mass and zero diameter, made of
 S> a single dimensionless fiber, stretched to a certain tension across a
 S> certain distance, between two infinitely rigid points. If you pluck
 S> exactly in the center, you will get only odd harmonics (try it on an
 S> acoustic guitar and see how much it sounds like a square wave!). If you
 S> pluck it close to one of the rigid endpoints, you will get both even and
 S> odd harmonics. The closer to the endpoint, the narrower the "pulse"
 S> gets.

For the lowers of hardcore theory I can recommend the book "Vibration
and Sound" by Philip M. Morse ISBN 0-88318-876-7 from Acoustical
Society of America.

And when you got yourself properly into the life of the string and how
it swings around it axis and all that... then you can start look at
the complex shapes on 2D surfaces like the face on a drum... the 808
doesn't come close to simulate that ;)

 S> Analog synthesis is far from the real mechanical world, where strings
 S> have mass and diameter and the metal stretches and heats. In a way it
 S> lets you listen to one parameter at a time, stripping away all other
 S> effects that would complicate the sound, allowing you to add more
 S> parameters one by one. If you really want to simulate a real string, you
 S> can, but it would take a *lot* of individual parameters and therefore a
 S> *lot* of synthesizer modules. But why do that? Analog synthesis is not
 S> about doing that - that's what samplers and physical modelling DSP's are
 S> for. For me, the sounds of the naked laws of nature are every bit as
 S> interesting as the complex "real" sounds. I love the sound of a hi-res
 S> 4-pole lowpass as it slowly picks out the harmonics of a bright
 S> waveform.

 S> Speaking of interesting harmonic sweeps, this reminds me of a pulse
 S> shaper that I came up with a while back that produced really interesting
 S> sounds. It was an expansion of a circuit in Electronotes (the "Dual
 S> Pulse Waveform Shaper") which used four comparators to create a
 S> symmetric-around-ground pulse width modulated waveform. If you feed it
 S> with a triangle wave and sweep the PWM input, you will get a PWM'ed
 S> sound with only odd harmonics (i.e. satisfying the mirror-image
 S> requirements). I'd forgotten about this - now I want to build one again!

Speaking of said waveshaper that Gene did. I have the schematic on a
scrole of faxpaper and have said that I will put it on the web, but
never got around doing it (my machine is simply too slow for the tools
that I use, and I have said that I am buying a new for months now).
The CV will change the quantization stepsize, quite interesting. I
would allow to do a dry/wet-mix pan-pot on this baby...

On the same scroll of faxpaper there is a CV-controlable ADSR!
Also in for webification... I guess I am not as free tomorrow as I
thought :->

Cheers,
Magnus



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