Adding feedback to a delay line creates decaying echoes whose rate is set by the gain multiplier

A single delay repeats a sound once. Feeding the delayed output back into the delay input creates a recirculating loop: each pass yields another repetition attenuated by the feedback gain (a scalar 0-0.99). With gain 0.5, amplitudes decrease as 0.5, 0.25, 0.125, forming an exponential decay. Gain of 1.0 produces non-decaying infinite repetitions; gain above 1 causes runaway amplitude. In Max, delay~ cannot form a feedback loop — only the tapin~/tapout~ pair allows feedback because their connection is a shared circular buffer reference, not an audio cable.

Examples

tapin~ 2000 / tapout~ 300 with *~ 0.7 feedback: echoes at 300, 600, 900 ms at 70% of the previous. Adding vs.butterlp~ inside the feedback loop simulates tape delay (progressively darker). DC offset guard: insert vs.butterhp~ at 10 Hz inside the loop.

Assessment

Draw a signal-flow block diagram of a feedback delay. Calculate amplitudes of the first 4 repetitions at initial amplitude 1.0 and gain 0.6. Why must gain stay below 1?