Lexicon LXP-15-II Owner's Manual page 41

Vibrato is the effect produced by small, regular variations in a sound's pitch;
guitar vibrato, for example, is created by alternately stretching and relaxing the
strings. The LXP-15 II can create automatic regular vibrato for a single instru-
ment, or mix of sounds, by means of sine wave modulation (LFO) of Glide Delay
or Pitch fine. Personal control of the rate of vibrato can be created by patching
an external foot pedal to the LFO.
Short delays (5ms) should be used with no feedback, and 100% delayed sound
fed to the output. Moderate depth is more natural sounding, especially with
realistic rate settings. (Both depend on the instrument and the music.)
True doubling is done by having a performer overdub a performance on a
different track of a multitrack recorder. When the "takes" are synchronized, the
normal variations in each performance provide enhancement — the effect is to
"thicken" vocal tracks. Synthetic doubling combines the original sound with a
delayed version (30ms) in order to make a single performer sound like two or
more. The illusion of double tracking can be greatly improved by introducing a
small amount of pitch vibrato (modulation of Glide Delay or Pitch fine), particu-
larly if some envelope follower modulation (InLvl) is combined with sine wave
modulation (LFO). This makes the pitch variations seem more random, more like
what actually happens when a performer dubs in a second part.
Chorusing is closely related to the doubling effect, but is more suggestive of a
rotary speaker. The delay times used are usually somewhat shorter (20ms), the
LFO modulation may be a little more exaggerated and, very often, feedback is
introduced to increase the intensity of the effect. There are many possible
variations of the chorusing effect; some shade into flanging, or doubling, or even
echo. The LXP-15 II provides a Chorus Delay algorithm which allows all of these
variations.
Originally, flanging effects were created by simultaneously playing two identical
programs on two tape recorders. By using hand pressure against the flange of
the tape reels, one machine was slowed down slightly, then the other. The result
was a series of changing phase cancellations and reinforcements, providing a
"comb filter" and a characteristic swishing tunneling and fading sound.
Flanging with a delay is much simpler; two tape recorders need not be kept in
relative sync. In fact, no tape machine is necessary — flanging can be done as
a live effect. A short delay (5-10ms), modulated by an LFO, is mixed with the
original signal, causing cancellation (nulling) at a frequency whose period (the
time for one cycle) corresponds to twice the delay time. Cancellation also occurs
on odd harmonics of that frequency. The depth of cancellation depends on the
level balance of direct and delayed sounds; maximum cancellation occurs at a
50-50 mix.
The flanging effect can be further altered by recirculating the delay with the
feedback control. Larger amounts of feedback cause exaggerated "deep"
flanges. Use of the envelope follower produces an interesting "talking flange";
where a sweep is produced for each attack of the input. Envelope and sine wave
modulation can be mixed for a complex sweep which is really quite pleasing.
Creating Sounds and Effects
Vibrato
Doubling
Chorusing
Flanging
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