Upcon Algorithm - Limit Page - TC Electronic UpCon Manual

UpCon algorithm – Limit page
Fig. 40.: UpCon algorithm – Limit page
The Limiter uses true-peak detection exceeding
the oversampling requirements of BS.1770.
UpCon English Manual (2014-10-07)
True-Peak Limit section
Threshold parameter
Threshold
Use the Threshold parameter to set the true-
peak Limit Threshold for all limiters.
True-peak detection makes overload of down-
stream devices, such as data reduction codecs,
sample rate converters and DA converters, less
likely. Though digital samples may go to full
scale, it is recommended to use a conservative
Limit Threshold, even in digital transmission. Re-
serve the top of the digital scale for occasional
peaks in wide range material (feature films, clas-
sical music), so don't go above -6 dBFS in HDTV
for normal broadcast programming. This way,
down-mixing or bass management at the con-
sumer will also not generate unexpected distor-
tion.
The distance between the Target Level of the
ALC section and the Limit Threshold is an impor-
tant audio quality defining factor – the so-called
headroom. Analog TV only had around 10 dB of
headroom, but DTV should have at least 15-16
dB of headroom for a chance of conveying audio
of a decent quality.
Raising the headroom can be accomplished by
moving down the Target Level and/or raising
the Limit Threshold. The headroom in BS.1770-
based standards is typically 22 dB – significantly
more than broadcast ever had before.
The UpCon algorithm
Link parameter
The Link parameter defines how limiters work
together.
C, LR, LFE setting
►
If the threshold is exceeded in the Center
channel, only that channel is limited.
►
If the threshold is exceeded in one of the oth-
er Main channels, all Main channels excluding
Center are limited.
►
If the threshold is exceeded on the LFE chan-
nel, only that channel is limited.
LCR, LFE setting
►
If a threshold is exceeded in one of the Main
channels, all Main channels are limited.
►
If the threshold is exceeded on the LFE chan-
nel, LFE is limited independently.
All setting
► If a threshold is exceeded in any channel, all
channels are limited.
Profile parameter
Use the Profile parameter to optimize the adap-
tive true-peak limiter based on content, or based
on the output platform.
The available settings are:
94