[sdiy] Thoughts on drum synth

[Tim Ressel]

Hi Y'all,

Thought I would toss in my thoughts on the subject of
drum synthesis. According to Olsen's "Music, Physics
and Engineering", a drum has a six modes of
oscillation which have a non-harmonic relationship.
Here are the freqs:

1st mode      Fo
2nd mode      1.59Fo
3rd mode      2.14Fo
4th mode      2.3Fo
5th mode      2.92Fo
6th mode      3.6Fo

Decidedly non-harmonic. As any frum player can tell
you, where you hit the drum head changes the tone.
What is happening here is different modes are being
excited depending on where the drum head is struck.

So it seems to me what we have here is six sine
oscillators and six VCAs. The amplitude of the VCAs is
determined by the drum 'hit'. This is complicated by
the fact that a drum 'hit' can excite more than one
mode, and to differing degrees. Having fun yet?

If we drill down deeper, we find that the body of the
drum forms a bandpass filter. A tom or kick drum body
will be a single pole BPF with a real low Q. A Doumbek
will have a more complicated filter structure.

Now it seems a waste to dedicate complex VCOs just to
make fixed freq sines. This sounds more like a bank of
NCOs, which in turn sounds like a DSP. 

Six modes of oscillation suggests six different places
to hit our virtual drum. Plus a way to tell it what
pitch to be at. Any thought on an interface?

This scheme would be adaptable for all different kinds
of percussion. 

This sounds like a lot of fun. A group project,
perhaps?

--TR

*****************
When in Doubt,
Play some Tomita
*****************


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