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KDFX Reference
KDFX Algorithm Specifications
954 Compress/Expand
955 Comp/Exp + EQ
A stereo soft-knee compression and expansion algorithm with and without equalization
PAUs: 2 for Compress/Expand
3 for Cmp/Exp + EQ
These are a 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.
Compression is expressed as a ratio: the inverse of the slope of the compressor input/output characteristic.
A compression ratio of 1:1 has no effect on the signal. An inÞnite ratio compresses all signal levels above
the threshold level to the threshold level (zero slope). For ratios between inÞnite and 1:1, increasing the
input will increase the output, but by less than it would without compression. The compressor is a soft-
knee compressor, so the transition from compressed to linear is 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.
Figure 10-80 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
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