[sdiy] karplus-strong drum synthesis

[Scott Gravenhorst]

Joel B <onephatcat at earthlink.net> wrote:
>While we are discussing algorithms, I'm attempting to figure out 
>how to write a karplus-strong drum synth function, the one on 
>page 46 of this document: 
>
>
>http://www.eumus.edu.uy/eme/cursos/dsp/material/karplus-strong/Karplus-Strong_Digital.Synthesis.of.Plucked-String.and.Drum.Timbres.pdf


Wow, thanks for that.  I've done a little playing with drum sounds using Karplus-Strong.  My setup
was a delay line (RAM) connected to a single pole lowpass IIR filter and back into the delay line.
 If the filter's Fc setting is high, the system sounds like a tight string.  If the Fc setting is
very low, the tones were very percussion like.  Wood block at least.  In my case, I excited the
delay line with a pulse.  Pulse width affect the timbre.

>
>I'm trying to figure out how to write this, looks like I need to 
>start with a wavetable of random numbers and somehow process it 
>like this: 
>
>y[ sample ] = ( y[ sample-p ] - y [ sample - p - 1 ] ) * blend - rnd(0) 
>
>where rnd(0) gives me random numbers less than one.
>
>p is supposed to be the output pitch if I understand correctly.
>
>Assuming i'm even a little bit right about this, the question is, 
>if I start at sample 0, there is no sample - 1 to use in the 
>equation, so how is that the condition handled? Do you wrap to 
>the last sample at t the end of the wavetable? 

Yes, it's a wavetable but also a delay line.

-- ScottG
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