All pass delay line with cubic interpolation which uses a buffer for its internal memory. See also BufAllpassN which uses no interpolation, and which BufAllpassL uses linear interpolation. Cubic interpolation is more computationally expensive than linear, but more accurate.
The input signal.
Delay time in seconds.
Time for the echoes to decay by 60 decibels. If this time is negative then the feedback coefficient will be negative, thus emphasizing only odd harmonics at an octave lower.