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DUAL/STEREO COMPRESSOR/NOISE GATE CN-220
Finally, it is advisable to try different musical programs and to vary the mixer equalisation in
order to make a final touch in the output level control.
Once the compressor is adjusted to, your liking it is as well to put the plastic protection lead
and to seal it if necessary.
SELECTIVE SOUND PRESSURE LEVEL CONTROL
The sound transmission level through a body depends, among other things, on the frequency
(the low sounds are more transmitted than the high-pitched through the walls), and therefore there
are times when a selective sound pressure level control is necessary, in order to make possible to
increase the power later.
In order to do that, insert the equalised signal in the SIDE CHAIN input, as explained in section
INCREASING THE OUTPUT LEVEL OF A MIXING SIGNAL . The equaliser must be adjusted by imitating
the sound transference operation through the wall. Because of this, this transference operation has
to be measured (for instance; by using an spectrum analyser) in the room we want to "isolate" from
these frequencies. Of course, this measurement will be made in the usual pressure conditions of the
hall.
This procedure, extensible to any frequency band, can be a great resort for problems in the
transmission of structures, without having to reduce excessively the global level of the room because
of it.
TIME CONTROL
In many local legislations, the allowed sound pressure levels depend on the time of the day,
and because of it is very usual to operate the compressor/limiter only from a certain time. In order to
accomplish this, we will use an standard time switch and a relay with a 220 VAC. coil and with a
double reverse circuit, connected as explained in attached picture. The time switch will be protected
in a sealed box with legal purposes.
As can be seen in the block diagram, the signal controlled by the detector, and therefore the
compressor dynamic, pass through the SIDE CHAIN connector, in such a way that the compressor
will stop compressing if we interrupt it. With the relay activated (as showed in the picture), the
compressor will start operating. The signal cable must be short and screened, because the primary
circuit goes to the mains.
To avoid noises or mains isolations, it is better to put a transformer of 220 to 12V in the time
switch output, for instance, and use a relay of 12 V. of alternate. Another solution may be to use a 9
or 12 V. converter of DC and use a relay of DC of 9 or 12 V, being perhaps the most safe and
economic.
