--- /dev/null
+
+/* Stereo flanger with feedback. */
+
+/* This is basically just a chorus with a different kind of LFO (triangle wave
+ instead of sine), smaller delay times (typically 1-10 ms instead of 20-30
+ ms) and (much) larger sweep depth, which makes this unit sound more like a
+ time-varying filter (in fact, that's just what it is), in contrast to the
+ gentle pitch modulation produced by a chorus.
+
+ There's also an additional feedback loop which can be used to produce
+ metallic sounds, and a stereo control which allows you to change the
+ stereo spread (a.k.a. phase difference between left and right LFO).
+
+ Note that you can actually make this unit sound pretty much like a chorus
+ by cranking up the delay time while setting the feedback to zero and
+ reducing level and depth (the latter by at least an order of magnitude). */
+
+declare name "flanger -- stereo flanger with feedback";
+declare author "Albert Graef";
+declare version "1.0";
+
+import("music.lib");
+
+level = hslider("level", 1, 0, 1, 0.01);
+freq = hslider("freq", 2, 0, 10, 0.01);
+dtime = hslider("delay", 0.002, 0, 0.04, 0.001);
+depth = hslider("depth", 0.5, 0, 1, 0.001);
+feedback = hslider("feedback", 0.1, 0, 1, 0.001);
+stereo = hslider("stereo", 1, 0, 1, 0.001);
+
+tblosc(n,f,freq,mod) = (1-d)*rdtable(n,waveform,i&(n-1)) +
+ d*rdtable(n,waveform,(i+1)&(n-1))
+with {
+ waveform = time*(2.0*PI)/n : f;
+ phase = freq/SR : (+ : decimal) ~ _;
+ modphase = decimal(phase+mod/(2*PI))*n;
+ i = int(floor(modphase));
+ d = decimal(modphase);
+};
+
+triangle(t) = ((0<=t) & (t<=PI))*((2*t-PI)/PI) +
+ ((PI<t) & (t<=2*PI))*((3*PI-2*t)/PI);
+
+flanger(dtime,freq,level,feedback,depth,phase,x)
+ = (x+(loop(x)*level))/(1+level)
+with {
+ t = SR*dtime/2*(1+depth*tblosc(1<<16, triangle, freq, phase));
+ loop = (+ : fdelay(1<<16, t)) ~ *(feedback);
+};
+
+process = vgroup("flanger", (left, right))
+with {
+ left = flanger(dtime,freq,level,feedback,depth,0);
+ right = flanger(dtime,freq,level,feedback,depth,stereo*PI);
+};