Delay the spectrum, not the waveform. The signal is taken apart into frequency bins, each bin is delayed by its own number of hops, and the result is put back together, so the top of a chord can land before its bottom, a drum hit can smear into a sweep from bright to dark, and with feedback each band repeats on a clock of its own. The spectral blur smears energy across time and frequency; this moves it.
The curve
Three controls draw it. Low delay is what everything below the centre waits; high delay is what everything above it waits; the crossing is a raised cosine over four octaves centred on the centre frequency. At the defaults the lows are on time and the highs arrive 400 ms later, so a pluck turns into a pluck followed by its own shimmer.
Feedback
Each band’s repeat is fed back into the same band, so a band delayed by 400 ms repeats every 400 ms and one delayed by 50 ms repeats every 50 ms, and the two decay at the same rate per repeat rather than per second. The tail of a high feedback setting is bounded at 12 seconds on export, as the echo’s is.
Spread and mix
Spread mirrors the curve on the right channel, which widens anything with content on both sides of the centre. Mix blends the delayed spectrum with the dry signal; at 100 only the delayed bands are heard, and a band set to zero delay passes through unchanged.
Resolution
The transform is a 46 ms window hopping a quarter of its length, Hann in and Hann out. A delay is a whole number of hops because that is the one case where delaying a bin is exactly delaying that band. The window also sets the frequency resolution: below about 100 Hz the bins are wide, so the curve’s lowest octave moves together.
In the audio workflow
The step declares its one window of latency and the dry path is held back to match, so chaining it before a reverb or a limiter keeps everything aligned.