15
Gated AGC
AGC, or Automatic Gain Control, is a slow gain riding function of
the 261, analogous to a conscientious board operator closely watch-
ing the level meter and regulating the audio level very gradually.
AGC is sometimes also called leveling, and is useful in erasing the
long-term
audio level variations that are a normal result of operator
inattention, inconsistency between music cuts, or even the response
or interpretation of volume-indicating meters. AGC should have
negligible audible effect, serving instead to deliver a more constant
level to subsequent limiting and compressions stages so that they
might provide more consistent results.
AGC Response
The actual
response
of the AGC circuit to program material is quasi-
peak-responding, with an integration characteristic similar to that
of a European PPM. The
correction rate
, on the other hand, is slow
and unobtrusive.
AGC is enabled by scrolling with the
q
button to the next screen.
With the
w
cursor positioned as shown above,
t
and
u
may be used
to toggle the AGC among its three modes:
OFF
,
NORMAL
and
FAST
.
Gating Defined
and the
GATE Indicators
An AGC or other processing function is said to be
gated
when gain is
held, or locked, during brief pauses in the program. This prevents
background sounds from increasing to unnatural proportions; think
of crickets in the background of a movie dialog track.
When Model 261 AGC is enabled, a gate indicator box appears
above the
0dB
mark. The box is empty when the gate is closed;
that is, during pauses in speech or when no program is present. The
box becomes a solid block when the gate is open and the AGC is op-
erating.
The AGC has a resting value at the
0dB
point on the
AGC GAIN
scale. A proper adjustment of Model 261 input gain causes the AGC
to hover around the
0dB
mark most of the time that the AGC is op-
erating. When the gate closes, AGC gain will slowly return to the
0dB
resting point.
