Auto Level Control - RME Audio ADI-96 PRO User Manual

9.82 ALC
The ALC operates with two different attack times. Headroom 1 to 6 dB uses an attack time of 3
ms, Headroom 7 to 12 dB of 6 ms. The picture printed below shows the internal operation of
the ALC. The left channel (top) is amplified by the defined Gain (in this case 10 dB), as the
defined average level (0 dBFS minus Headroom) isn't reached. The right channel (bottom)
shows the unprocessed signal.
A higher input level at this gain
setting will either exceed the av-
erage level (0 dBFS minus Head-
room) or even the maximum level
of 0 dBFS. Then the ALC imme-
diately begins to reduce the am-
plification to avoid overloads.
After 3 ms (or earlier) the signal
level is back to a correct state.
Exceeding the maximum level in
this short time will cause precise
clipping. Because of the short
time this clipping occures there will normally be no noticeable side effects. In case the input
level drops the ALC will begin to raise the level, with a speed according to the time set under
Rise. This technology results in an extraordinary digital Compressor. The precise and controlled
clipping leads to an analog behaviour and 'punchy' sound characteristic.
A level control without any clipping can be achieved by using the ALC in Look Ahead mode. As
with the Expander activating the Delay and setting a sufficient delay time will avoid any clipping
and lead to an extreme clean processing. Usual settings between 5 and 10 dB Gain need only
4 ms to prevent clipping. Very high Gain settings (up to 24 dB) require greater preview times.
25 ms is enough for secure operation at any possible setting.
The sound difference between Look Ahead and normal operation can easily be checked in
realtime by simply switching the Delay on and off.
G
The usage of Look Ahead leads to a delay of the digitized signal, which might be a serious
problem in recording situations where realtime behaviour is required. Please note that the
function ALC was optimized to give excellent results even without Look Ahead.
The preview time of Look Ahead is internally limited to 25 ms. Higher delay times will not result
in a longer preview time. This guarantees a correct correlation between audio and control sig-
nal.
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User's Guide ADI-96 PRO © RME