Alto Professional ACOM2 - Manual (Page 6)

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Ratio Control
This control sets the ratio of input level to output level but only for the signals that exceed the threshold. The
scale of the ratio control on the front panel (calibrated in dB) indicates how much input level is required to
decrease the output level by 1 dB. If you have a ratio equal to 1:1 you will get the same level of input and
output signal: no level change.
If you have a ratio of 2:1 this means that for every 2 dB increase of the input level (above the threshold) you
will get an increase of output level of only 1 dB. Similarly, a ratio of 10:1 means that every 10 dB increase of
the input level above the threshold results in an output level increase of only 1 dB. Essentially, the greater the
ratio, the more compression is applied to the signal above the threshold. Higher ratio settings produce less
natural sounds, so use a ratio of 4:1 or lower if you want only a subtle effect on the dynamic range of a
source.
Attack control
The attack control represents the amount of time it takes before the compressor starts to lower the output
level when the signal is above the threshold point.
We recommend using a short attack time for very fast transients, such as drums, handclaps, etc. These
peaks are carefully regulated by the compressor. When setting the attack control, start with longer attack
times and gradually reduce it until you reach an optimal setting. The minimum attack control time is 1
millisecond; the maximum is 200 milliseconds.
Release control
The release control determines how much time the compressor needs to return to normal gain when the
audio signal falls below the set threshold. A release time that is too short will make the volume fluctuate,
resulting in a "pumping" effect. A release time that is too long will produce a "pumping" and breathing effect,
especially when you have a loud passage followed by a quiet passage. The minimum release time is .05
milliseconds; the maximum is 4 seconds.
Auto switch
This switch activates an intelligent program recognition circuit, which automatically sets the optimal attack
and release times while also avoiding distortion and pumping effects. When activated, this switch disables
the manual attack time and release time settings.
Output control
This control compensates for the loss of level generated by the gain reduction caused by compression and
limiting.
Effect switch
This switch turns off the corresponding channel, which is useful for comparing the processed and
unprocessed signal.
8
:1
Output
Input
Threshold
Gain 0 dB
Ratio 2:1
Ratio 4:1
Limiter