BSS Audio DPR 522, User Manual

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This type of filter not only allows band-pass configurations, but also, by the
appropriate setting of the KEY FILTER and WIDTH controls, the conventional
low pass or high pass configurations can be easily realised. Experience will
show that this approach gives considerable operational advantages for the user
over the more simple separate low/high pass filter approach.
6.4 Key listen
When this switch is depressed, it connects the output of the key filter to the
output connector instead of the normal signal. This makes it very easy to
adjust the KEY FILTER and WIDTH controls to ‘home in’ on the signal that is
required to open the gate. To enable both hands to be used for adjusting the
key filter, this switch is latching, and may therefore be left engaged by
accident rendering the gate function inoperable - the switch illuminates red to
warn you of this.
6.5 Ext key
6.6 Threshold
The filtered key signal is passed to the THRESHOLD control. The numbers
around the THRESHOLD control indicate the approximate level in dBu that
will be required from the key filter in order to just cause the gate to open.
With the control fully clockwise in the ‘out’ position, the gate will be held
closed at all times. As the control is rotated anticlockwise, the threshold point
is progressively reduced, or becomes more sensitive. You will find that as you
set the WIDTH control narrower, it is generally required to reduce the
threshold level to compensate for the smaller amount of energy being passed
from the filter.
Control operations
Normally with this switch out (un-illuminated), the input to the key filter is
taken from the main input, allowing the main signal to gate itself. If it is
desired to use other audio signals as a trigger, these may be applied to the
rear panel KEY RETURN socket with the EXT KEY switch depressed. This
signal can be heard by depressing KEY LISTEN, and both the filter controls and
gate control will now work on this signal.