Moog 500 Series User Manual download pdf (Page 15)

LFO AMOUNT: A setting of 0 volts or GROUND sets the LFO AMOUNT at

zero while a 5v setting sets the AMOUNT to maximum. To modify the LFO

AMOUNT from minimum to maximum via control voltage or expression

pedal, set the LFO AMOUNT control to the lowest setting via the editor or

MIDI message.

LFO SHAPE: A setting of 0 volts or GROUND sets LFO SHAPE to OFF

while a 5v setting sets SHAPE to Smooth S-H. To modify the LFO SHAPE

from minimum to maximum via control voltage or expression pedal, set the

LFO SHAPE control to the lowest setting via the editor or MIDI message

NOTE: An expression pedal used with the Analog Delay should contain a

50K Ohm linear taper potentiometer. Other values will work at either re-

duced range or increased noise.

ABOUT ANALOG DELAYS

A delay circuit produces a replica of an audio signal a short time after the

original signal is received. If you listen to the original (direct) signal and the

delayed signal together, the delayed signal will sound like an echo of the di-

rect. To make a whole series of echoes that die out gradually, you feed the

delayed output signal back to the input. You can determine how far apart

the echoes are by adjusting the delay time of the delay circuit, and you can

adjust how fast the echoes die out by adjusting the amount of feedback

from the delay. In addition, you can determine how loud the echoes are by

adjusting the mix between the direct signal and the delayed signal.

During the early 1970’s, large-scale semiconductor analog delay circuits

became available. These are called Bucket Brigade Delay (BBD) chips, be-

cause they function by passing the audio waveform down a chain of several

thousand circuit cells, in analogy to water being passed by a bucket bri-

gade to put out a ﬁre. Each cell in the chip introduces a tiny delay. The total

time delay depends on the number of cells and on how fast the waveform

is “clocked”, or moved from one cell to the next.

In the Analog Delay, the LFO creates a control voltage that is used to

modulate the time function of the delay. The BBDs in the Delay Line

contains 8192 “buckets”. With the time unmodulated the signal spends

the same amount of time in each bucket based on the selected delay time.

With the time modulated by the LFO, time is no longer a linear function

and audio signals already in the buckets get compressed or stretched. A

good analogy for picturing this is a clock with a sweep hand to show the

seconds. Imagine that you could hold the sweep hand and either slow it

down or speed it up. Yet, when you let it go the sweep hand instantly went

to the correct position on the clock face. In a sense, this is how the LFO

modulates the Delay Line.

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Moog 500 Series User Manual Page 15