API The BOX Operator's Manual page 54

API "The BOX"
Compressor Circuit Topologies
The 527 compressors can be set to operate in two circuit topologies:
OLD: Feed-back: The RMS detector receives the signal from after the VCA
•
NEW: Feed-forward: The RMS detector receives the signal from before the VCA
•
OLD: Feed-Back Compression
In a feed-back compressor, the RMS detector gets its signal from the output of the
gain reduction device (VCA). This is how older API 525, 1176 type, and 660 type
compressors work. This yields a smoother, softer, more transparent sound.
NEW: Feed-Forward Compression
In a feed-forward compressor, the RMS detector normally gets its signal from a split of
the input signal. (The detector path can alternately get its signal from a Side Chain
Input.) With this method, the RMS detector sends a signal to the VCA that is an exact
ratio of the desired compression set by the RATIO control. This is how many new VCA
based compressors work. This can yield more aggressive compression and a harder,
more affected sound.
TYPE (NEW-OLD): Toggles between feed-back and feed-forward
compressor topologies
OLD feed-back is selected when not engaged
•
NEW feed-forward is selected when engaged
•
Illuminates when engaged
•
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Operator's Manual