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EFFECTS MENU 567
Signal flow and steps
1) Phase reverse, Pad, Highpass
2) Optical compressor
The compressor of am-phibia is one of
the most gentle compressors available
on the market and is ideal for difficult
signals such as vocals. The fundamental
circuit is an emulation of a classic opto-
coupling design with a so-called
feedback circuit.
For this principle a light source (LED, light bulb or electro-luminescent panel) is fed with the
output signal. The emitted light is beamed onto a light-dependent resistor and the changes
to the resistance result in a change in the amplification factor of the entire circuit
(controllable voltage divider). The light source is fed from the output instead of the input
due to historical, practical reasons: the circuit gently oscillates to the signal and is very
stable without additional settings, and operates very musically so that, in hardware reality,
such a device can be built with a minimum amount of required components (to the benefit
of the sound quality). Due to the overall lag of the opto-coupling system, optical
compressors have a relatively sluggish release reaction. This is accompanied by the so-
called memory effect of the opto-coupler. A longer exposure to light also means longer
return times. Due to the feedback control, the control times and compression ratio also
highly depend on the control times, and the compression ratio strongly depends on the
input signal.
You can specify whether you want to tap the feedback signal after the gain stage or the
second filter. In combination with the pre-filter stage you can achieve a frequency-
dependent compression.