User Guide

FXAlg #954: Compress/Expand ¥ FXAlg #955: Comp/Exp + EQ
Algorithm Reference-147
FXAlg #954: Compress/Expand ¥
FXAlg #955: Comp/Exp + EQ
A stereo soft-knee compression and expansion algorithm
with and without equalization
Allocation Units: 2 for Compress/Expand; 3 for Cmp/Exp + EQ
These are stereo compressor and expander algorithms. One version is followed by equalization and the other is not.
The algorithms compress the signal level when the signal exceeds a compression threshold and expands the signal
when the signal falls below the expansion threshold. The amount of compression and/or expansion is based on the
larger magnitude of the left and right channels.
The amount of compression is expressed as a ratio. The compression ratio is the inverse of the slope of the
compressor input/output characteristic. A compression ratio of 1:1 will have no effect on the signal. An infinite
ratio, will compress all signal levels above the threshold level to the threshold level (zero slope). For ratios in
between infinite and 1:1, increasing the input will increase the output, but by less than it would if there was no
compression. The compressor is a soft-knee compressor, so the transition from compressed to linear is quite
gradual.
The amount of expansion is expressed as an expansion ratio. Expanding a signal reduces its level below the
threshold. The expansion ratio is the inverse of the slope of the expander input/output characteristic. An expansion
ratio of 1:1 will have no effect on the signal. A zero ratio (1:¥), will expand all signal levels below the threshold level
to the null or zero level. (This expander expands to 1:17 at most.) Thresholds are expressed as a decibel level relative
to digital full-scale (dBFS) where 0 dBFS is digital full-scale and all other available values are negative.
Compressor/Expander (optional EQ not shown)
R Input
L Input
Maximum
Magnitude
Expander
Computation
Compress/
Expand
Compress/
Expand
Compress/
Expand
Compress/
Expand
Magnitude
Maximum
Delay
Delay
Computation
Compressor
Feedback/Feedforward
Switches
L Output
R Output
Out Gain