Useful for reverberation, especially implementing Gardner reverbs.
DoubleNestedAllpassL.ar(in, maxdelay1: 0.0047, delay1: 0.0047, gain1: 0.15, maxdelay2: 0.022, delay2: 0.022, gain2: 0.25, maxdelay3: 0.0083, delay3: 0.0083, gain3: 0.3, mul: 1.0, add: 0.0)