From Wikipedia:

The shortest delay time you can set with the DELAY control is 5ms. That gives a repeat rate of up to 200 repeats per second. Repeats from about 20 times per second are repeating at audible audio frequencies. This creates a type of effect called a comb filter.

[strong]Control Settings[/strong]

MODE: ECHO
FX LVL: Max Effect
DELAY: From Minimum to about 9:00
FEEDBACK: from about 3:00 to just shy of runaway feedback (About 4:00)

[strong]Playing Tips[/strong]

Start with the control settings as above. Now play some notes. Start [strong]slowly [/strong]turning the delay to the right while you’re playing some notes. Don’t go past about 9:00. You’ll hear the harmonic resonant frequencies of the delay time change while you sweep the knob between about 7:00 and 9:00.

The range for controlling this effect is very small. As the delay time increases beyond audio frequencies you start to distinguish individual repeats and this no longer creates a comb filter. Comb filters tend to have sweet spots that are in the harmonic series of the frequency of the repeats, so you usually have to poke around for them. Try playing scales up and down the neck to find the sweet spot. You can move that sweet spot by slowly sweeping the delay setting.

Because of the massive harmonics caused by the constructive and destructive interference, this is primary a monophonic effect, but try whatever you want to. You can decrease the intensity of the effect with the FX LVL setting, but you’ll get the most traditional comb filter effect by balancing the mix of dry to wet signal so that the dry can interfere with the wet.