8.2.7 Module:
Expander
In practice, expanders are mostly used for suppressing interferences (background noise, tape noise)
in modulation pauses.
Signals whose level is higher than the value set with
Threshold
are not influenced. These are the
signal portions you want to keep.
If the signal level is below the
Threshold
value, it will be attenuated. These are the signal portions (e.g.
background noise) that you want to remove.
The
Threshold
setting is therefore most important. The use of an expander requires an exact
knowledge of the technical context since parts of the useful signal are possibly “suppressed” if it is set
improperly.
If you are not sure whether or not to activate this function, switch off this module.
Functions and settings in detail:
Ratio
The ratio parameter defines the expansion ratio of the module. A ratio setting
of 1:2 means that if a signal level is 1 dB below Threshold level, it will be
attenuated by 2 dB. The higher the set value, the more the signal will be
attenuated by the expander. The ratio setting range is 1:1 to 1:3.0.
Threshold
This parameter controls the threshold of the expander. Above the level value
defined by Threshold the expander will operate as a 1:1 gain stage. Below the
threshold the expansion ratio set with the Ratio parameter is applied to the
signals. The threshold setting range is –60 dB to 0 dB.
Output Gain
This controller can be used to increase the output gain of the expander
independently of the input level. The gain setting range is 0 dB to +20 dB.
Attack
This controller controls the response time of the expander. The smaller the
time constant set here, the faster the expander will respond to a signal
overriding the threshold (“Opening-time”). For the slow position of the
controller (left stop) the attack side is approximately 12 ms; for the fast
position (right stop) it is approximately 0.4 ms. These are guide values, they
vary depending on the dynamic and spectral characteristic of the input signal.
Release
This controller controls the closing time of the expander. The higher the time
constant set here, the slower will be the attenuation of the signal after falling
below the threshold. For the slow position of the controller (left stop) the
release time is approximately 2.048 ms; for the fast position (right stop) it is
approximately 16 ms. These are guide values, they vary depending on the
dynamic and spectral characteristic of the input signal. Short release times are
critical. If you are not yet familiar with the handling of an expander, use
medium to extended times first.
Note: The expander is a dynamic tool with the reverse effect of a
Compressor
. Its application is
especially recommended if a compressor is used at the same time.
A
Compressor
(or the
AGC function
) may often emphasize parasitic noise in signal intervals.
To avoid this, arrange an expander before the compressor (and/or
AGC Module
) in the signal path.
Adjust the threshold to a value higher than the parasitic noise and lower than the useful signals.
VIP
digital
Manual 4.0 Yellowtec 2004 Rev. 26.07.2004
Page 47
