All analog delays have two essential ingredients: the bucket brigade device and the clock
The BBD is made up of hundreds or thousands of tiny mosfet transistors (called steps) that delay the input signal via capacitive charging (each step may also be
referred to as a clock cycle). The more steps in the device the longer the signal can be delayed. This delay is measured in milliseconds.
The clock outputs a continuous square wave at a specific frequency. This frequency instructs the BBD as to the rate at which its steps “catch and release” the
signal. The clock (which actually outputs two frequencies 180° out of phase) can also be altered over a range to change the rate at which the BBD processes the
signal. It is this range that changes the delay signal from short to long.
This type of design has two major caveats: the clock generally operates on a frequency that is within the human range of hearing and the signal processing of the
delay degrades the input signal continuously. The lower the clock frequency, the more delay you get, but the further it creeps into the audio range.
Analog delays attempt to optimize the balance between signal degradation and clock bleed by a series of additional signal processing chains. These are
compression, filtering and expansion. The compressor portion “beefs up” the incoming signal to minimize its degradation while traversing the BBD. The filtering
removes some of the high end content so that the clock does not bleed into it (which would create a high pitch whine). Finally the expandor portion “de-
compresses” the processed signal and gets it ready for the output mixer.
This entire process is also responsible for creating the “magic” and “mojo” of the analog delay. That magic is warmth. The continuous filtering of the guitar signal
removes more and more high end frequencies with each repeat which the ear perceives as warmth in the resulting guitar signal. This is why people like analog
delays so much---they create a very pleasing “bed of sound” that is neither too piercing nor distracting. Each analog repeat fits neatly under the preceding one to
create a very natural and musical sound.
Summary of Contents for ABDX
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