hello,

I'm thinking of having a go at writing a plugin for csound which produces 
synthesised drum sounds. The way I'm planning to do it is to find the roots 
of the bessel functions (solutions to the wave equation on a 2D circular 
sheet) to find the amplitude and frequency of the first several orthogonal 
frequency components, then synthesise these with a series of sine 
oscillators. The opcode would look something like:

adrum besseldrum ifreq iamp istrikeradius istriketheta idamp [ kmicradius1 
kmictheta1 kmicamp1 kmicradius2 kmictheta2 kmicamp2] ...

I.e. you could specify the base frequency of the drum, initial amplitude, the 
point on the drum where it was hit, a damping value, and then the locations 
of a series of 'microphones' which would pick up the resulting oscillations. 
The location of the strike point and the microphones would affect the balance 
of different frequency components in the output signal. It wouldn't be a full 
physical model like the waveguide opcodes - I'm planning to use the known 
solutions for this wave equation.

I've got a fairly good general idea of how to go about this, but if anyone has 
any advice I would appreciate it. Roughly what I'm planning to do is to use 
the initialisation function to work out the frequencies of the different 
components, create tables of the solutions to the wave equation, and set up a 
series of sine oscillators (based on the oscil opcode). The amplitude of each 
component would be initialised according to where the drum was hit. Then the 
main function would mix the outputs from each of the virtual microphones into 
an output signal.

The sort of thing that would be good to know is firstly if this is a valid 
approach to generating synth drum sounds? I'm not too worried about how much 
it sounds like a real drum, but it would be good to know if people have done 
this sort of thing before. Also if anyone has any general advice on writing 
opcodes for csound, that would be good. One thing I'm not sure about is what 
libraries to use to keep the code portable - the standard unix math library 
includes bessel functions, but I don't know if this is true for windows.

thanks, 

andy baxter

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Thanks, andy.


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