[sdiy] Karplus-Strong overblowing?

[rburnett at richieburnett.co.uk]

The original KS model is very basic as others have said. It really just 
models a single "round trip" delay with some (frequency-selective) 
damping and possibly some dispersion in the loop. That's fine for 
modelling things that are struck or plucked with transients like 
strings.

I believe wind instruments are more accurately modelled by Waveguide 
Digital Networks. These are networks of bi-directional delay lines 
coupled together by "scattering junctions." The scattering junctions or 
nodes determine how much of the output of one delay line couples into 
the next, how much reflects back into the original delay line 
(propogating in the opposite direction,) and how much is absorbed (lost 
to heat, radiated, whatever.)

Then at the ends of the model you have non-linearities that control how 
the pressure waves interact with the Reed and blowing pressure at the 
blown end of the instrument, and the outside air pressure at the, erm, 
bell end ;-))

I think its these non-linearities at the ends that will be critical for 
modelling overblown behaviour.  The overall model must be non-linear if 
the behaviour changes when the amplitude of the excitation changes. 
Otherwise the strongly blown sound wound just be a louder, but otherwise 
identical, version of the softly blown sound. There wouldn't be a shift 
to a different resonant mode when over-excited.

Waveguide Digital Networks and physical modelling aren't really my 
thing, so i wont say any more as could be misleading or plain wrong. I'd 
do some reading of the physical modelling literature by Julius Orion 
Smith if you're into the theory. Or alternatively string together some 
delay lines and play about with scattering nodes, filters and 
non-linearities at the ends if you're into the practical/coding side. 
"Reed tables" appear to be one way to model the non-linear behaviour of 
the reed to pressure differences.

I hope this is some help. Interested to read other's comments and 
suggestions.

-Richie,


>>> Am 02.01.26 um 10:56 schrieb cheater cheater via Synth-diy:
>>>> Does Karplus-Strong synthesis allow for overblowing? Are there any
>>>> modifications to it that allow it?
>>>> 
>>>> Overblowing is when you blow into a reed instrument too hard and
>>>> essentially the fundamental becomes much weaker and the higher
>>>> partials become much stronger, kind of "overdriven".
>>>> 
>>>> Thanks
>> 
>> 
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