Expander; A Stereo Expansion Algorithm - Kurzweil K2661 Musician’s Reference Manual

952 Expander

A stereo expansion algorithm

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This is a stereo expander algorithm. The algorithms expands the signal (reduced the signal's gain) when
the signal falls below the expansion threshold. The amount of expansion is based on the larger magnitude
of the left and right channels. 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.
Feedback/Feedforward
Switches
Sum
Magnitude
L Input
R Input
Figure 10-106 Expander
To determine how much to expand the signal, the expander must measure the signal level. Since musical
signal levels will change over time, the expansion amounts must change as well. You can control how fast
the expansion changes in response to changing signal levels with the attack and release time controls.
The attack time is defined as the time for the expansion to turn off when the signal rises above the
threshold. This time should be very short for most applications. The expander release time is the time for
the signal to expand down after the signal drops below threshold. The expander release time may be set
quite long. An expander may be used to suppress background noise in the absence of signal, thus typical
expander settings use a fast attack (to avoid losing real signal), slow release (to gradually fade out the
Expander
Computation
Delay
Delay
Sum
Magnitude
Expander
Expander
KDFX Reference
KDFX Algorithm Specifications
L Output
Out Gain
R Output
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