Section 32: Outputs Tab
T
ieline
Page 282
T E C H N O L O G Y
32.4.
Talk Back Level Adjustment
This setting allows the user to set the minimum headphone talkback level. This
means that even if a commentator turns down the headphone level pot
completely on the codec, talkback will still be heard in the headphones. This is a
great safety feature to ensure continuity of communications. (Related Topic:
Talkback)
32.5.
Automatic Gain Control
As a default setting, automatic gain control (AGC) is enabled on the outputs of
T
ieline
codecs. AGC is independent of Intelligent Gain Control (
IGC
).
AGC is triggered if audio signals ap20dBu (+16 vu). This is to avoid
distortion of audio, which occurs if signals go beyond the analog stage limit of
+21dBu.
ACG has a very fast reaction time and will decrease high audio levels by
approximately 1dB every 2 milliseconds, up to a maximum of 44 dB of
attenuation. AGC tries to return levels to normal once the output dips below
+15dBu (+11 vu). This will increase the levels by 1dB every 2 milliseconds.
Another way of expressing AGC in as follows:
Output = Mix x AGC.
•
If output > +16 vu (+20dBu), AGC decreases levels by 1dB to a maximum of
– 44dB.
•
If output < +11 vu (+15dBu), ACG increases levels by 1dB to a maximum
0dB.
32.6.
Relationship of IGC to AGC
T
ieline
recommends the use of both
IGC
and AGC in most situations.
IGC
is a
transparent level adjustment mechanism across each codec input that keeps
levels in check, without coloring audio content with unwanted additional
processing. It also allows each input to be adjusted individually, retaining the
levels of other inputs when one is adjusted. This is different to AGC which is
across the outputs, and for which any gain reduction affects the mix of all audio
inputs simultaneously.
These thresholds are complementary to the settings for
IGC,
which is across
codec inputs. If
IGC
is enabled in
T
ieline
codecs it is enabled at +14dBu.
Enabling
IGC
avoids hard clipping of signals, which occurs in the digital input
stages if signals are higher than +14dBu. With
IGC
,
an
input will remain at the
lower level until it is readjusted by an operator.
IGC Auto Level
reduces high input levels to within acceptable limits and returns
levels automatically to the original settings when levels have returned to normal.
