# Waveguide with Excitation Input

This example is a first step towards excitation-continuous instruments, such as wind instruments. Instead of initializing the waveguides with a single excitation function, they are fed with an input signal.

// waveguide_input.dsp
//
// waveguide with excitation by input signal
//
// - one-pole lowpass termination
//
// Henrik von Coler
// 2020-11-19

import("all.lib");

// use '(pm.)l2s' to calculate number of samples
// from length in meters:

segment(maxLength,length) = waveguide(nMax,n)
with{
nMax = maxLength : l2s;
n = length : l2s/2;
};

// one lowpass terminator
fc = hslider("lowpass",1000,10,10000,1);
rt = rTermination(basicBlock,*(-1) : si.smooth(1.0-2*(fc/ma.SR)));

// one gain terminator with control
gain = hslider("gain",0.5,0,1,0.01);
lt = lTermination(*(-1)* gain,basicBlock);

// a simple allpass (Smith Paper)
s = hslider("s",0.9,0,0.9,0.01);
c = hslider("c",0.9,0,0.9,0.01);
allpass = _ <: *(s),(*(c):(+:_)~(*(-s))):_, mem*c:+;

// another allpass
g = hslider("g",0.9, 0,0.9,0.01);
allp = allpass_comb(2,1,g);

scatter = pm.basicBlock(allpass);

idString(length,pos,excite) = endChain(wg)
with{

nUp   = length*pos;
nDown = length*(1-pos);

wg = chain(lt : segment(6,nUp) : out : in(excite) : scatter : segment(6,nDown) :  rt); // waveguide chain
};

exc = select2(gain>0.9,1,0);

length = hslider("length",1,0.1,10,0.01):si.smoo;

process(in) = idString(length,0.15, in) <: _,_;