16
The previous illustration introduces a couple of other AGC options:
AGC Rate
(Speed)
The
NORMAL
setting for the AGC is the best choice for most process-
ing situations. The
NORMAL
correction rate of the AGC is very slow
and unobtrusive. Very tight pop-music formats, on the other hand,
may well benefit from more rapid AGC action offered in the
FAST
mode. The primary risk in using a faster AGC is the danger of gain-
riding action becoming audible under some circumstances. In an
interview situation, for instance, it may be more apparent that the
gain is being ramped up and down when the
FAST
mode is selected.
Classical and jazz music may suffer this risk as well.
The
FAST
AGC setting is always useful when setting up the 261, al-
lowing
INPUT GAIN:
to be set more quickly. AGC should probably be
reset to
NORMAL
once gain has been adjusted.
Maximum
AGC Gain
Typically, the AGC works
symmetrically
around a nominal 0dB
gain. When the level drops, AGC gain increases; when the level
rises, AGC gain goes into the negative region. The normal AGC
cap-
ture range
is ±15dB.
Some situations are better served with non-symmetrical AGC action.
Sportscasting and classical music are two examples. In both in-
stances, low-level events such as crowd noises and
pianissimo
pas-
sages are legitimate parts of the program. These may well be of a
sufficient level to open the AGC gate, but they do not want to be
brought slowly to full modulation by the AGC.
For this reason, a cap, or ceiling value, may be placed on the AGC
gain. Scrolling the
w
cursor down to
MAX AGC GAIN
allows the opera-
tor to set the maximum AGC gain at any value between
+15
d
B
and
0
d
B
. With
0
d
B
selected, AGC can bring
down
the level of loud pro-
gram material, but will not bring background sounds or low-level
music
up
to full level.
AGC
Range Alarm
The AGC has a stated capture range of ±15dB. This range should
be more than adequate for all situations, and the need for additional
long-term control indicates a problem elsewhere in the audio pro-
gram chain, suggesting a possible violation of signal headroom con-
straints as well.
Whenever AGC gain gets to the end of its ±15dB range limit, the
261 initiates an alarm. The flashing front-panel
AGC OUT OF RANGE
indication is shown on the next page. This is accompanied by a rear-
panel
AGC RANGE LIMIT
closure to ground for a remote indication.
