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Sound
> Control > Automatic Gain Control
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Imagine
a scene in a cabin with a person talking
and rain pounding down on the roof.
If you set the audio levels manually,
the result will be something like
the top chart. That is, the voice
will be much louder than the rain.
However, if the automatic gain control
is ON, then it will boost the sound
of the rain when the person pauses--because
automatic gain control always wants
something to be full volume.
The result will be something like
the chart below.
Play the demo above to hear
the "cabin" scene with automatic
gain control ON. Notice how
the rain sound is in the background--until
the person pauses. Then the automatic
gain control "hunts" and
brings the rain up full. It's pretty
annoying!
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Most
camcorders have an automatic setting that theoretically
gives you perfect audio levels with no fuss and no muss.
Sometimes,
these work fine. But this feature, called "automatic
gain control" has a dark side. You see, automatic
gain control will always try to ensure "pointing
straight up" audio levels. That's fine while your
subject is speaking. But what if he takes a long pause?
In that quiet moment, the automatic gain control will
hunt for whatever sound it can find--say the humming
air conditioner--and bring up that sound to "healthy"
levels. This is bad because you don't want to
increase the volume of the air conditioner during the
pause. You want it quiet during the pause.
As
a result, professionals NEVER use the automatic gain
control. Nonetheless, 90 percent of the time, it works
just fine on most camcorders.
Can
you tell I am somewhat conflicted on this topic? Here's
why: On one hand, pros never use automatic gain--for
the reasons described above. On the other hand, automatic
gain works quite well on most modern camcorders. Typically,
the first time students "go manual," they
do more harm than good! The bottom line is that it is
OK to use automatic gain when you are learning--with
the understanding that at some point, you'll need to
give it up and learn to control levels manually.
If
you want to experiment with manual control, the best
place to start is with an interview.
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