Threshold Offset
The analog audio level of the alpha compressor depends on the studio environment it is used in. In the ma-
jority of cases it depends on the D/A converter used, because the output stages of the converter determine
the analog level. As there is no binding norm for it, this level can be at +4 dB, +6 dB, +10 dBu, +12 dBu or
even +15 dBu. To make sure that the threshold controller actually covers its complete adjustment range it
can be adjusted to those different levels.
When is an adjustment necessary?
1. At low Ratio values (1:1.3), the threshold controller is al-
most completely turned clockwise and the gain reduction
is still too low
2. At higher Ratio values (1:2.5), the threshold controller is
turned completely counter-clockwise, but nevertheless gain
reduction already sets in
In order to adjust the internal threshold offset, the first thing
to do is to open the top cover with the adequate Torx screw-
driver. Before the adjustment can be done the unit has to be
powered up for at least 15 minutes to reach a stable working
temperature. Please make sure to disable the M/S and link
functions. Now send an audio signal into the compressor
and set the attack to approx. 24 and the release to 300 ms.
On the upper circuit board there is a blue trimmer labeled THRESHOLD OFFSET placed directly behind the
threshold potentiometer (yellow arrow in the figure). In the first case (too little gain reduction) the trimmer
has to be turned clockwise to raise the amount of gain reduction. In the second case (too much gain reduc-
tion) the trimmer has to be turned counter-clockwise. In order to reassure that the adjustment range now
really fits, it is recommended to repeat the above-mentioned test with the threshold controller in extreme
left/right position. The same procedure should also be applied to the right channel, of course.
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Threshold
The diagram shows different threshold settings in feedback mode. The threshold and the ratio are
always interdependent: On high ratios the threshold is usually set to lower values in order not to
produce too much gain reduction, and on lower ratio settings the threshold controller is turned
more to the right. The complete threshold range covers 33 dB which enables the user to make very
sensitive settings in reasonable steps at any time.
REFERENCE
