Stereo Flanger - ESI ESI2000 Operation Manual

Chorus
The function of a chorus device is to thicken the sound or to make one
voice sound like many. This effect is achieved is by mixing one or more
delayed versions of the signal in with the original. The delay times used
are too short to be perceived as a an echo, but long enough so that comb
filtering does not occur. In addition, the delay time is varied via a low
frequency oscillator to simulate the random differences that occur when
multiple instruments are playing together. A slight amount of feedback
improves the effect by creating multiple images of the sound as it
recirculates again and again.
All the choruses are true stereo using two separate delay lines controlled
by a single set of controls. The delay times are slightly different for each
channel and the LFO phase is inverted on one channel to help contrib-
ute to the overall chorus effect. The LFO Rate and Depth settings are
critical to achieving a realistic effect with faster LFO rates generally
requiring less LFO amount and vice-versa.
Doubling
When a copy of a sound, delayed by about 26 milliseconds, is added
back with the original, two audio images can be perceived by the brain.
When the delayed image is slightly varied or modulated, the illusion of
two voices is created.
Slapback
Slapback is a single short echo in the range of 50-60 milliseconds. A
sound delayed by this length of time is perceived as a discrete and
separate image which is useful for a thickening effect or as a pre-delay
for reverb simulating a hard, reflective surface such a gymnasium wall.

Stereo Flanger

A flanger consists of a short audio delay line whose output is mixed
together with the original signal. Mixing the delayed and original signals
results in multiple frequency cancellations called a comb filter. Since the
flanger is a type of filter, it works best with harmonically rich sounds.
FREQUENCY (log)
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ESI Operation Manual