Manual

ALC2
Loudness Pilot English Manual (2014-10-07) 94
Limit page
Fig. 45.: Loudness Pilot Limit page
The Limiter uses true-peak detection exceeding
the oversampling requirements of BS.1770.
Loudness normalization based on “perceived
loudness” can lead to peaks that might overload.
That’s why Loudness Pilot employs True-Peak
limiting. Your signal gets upsampled so that even
inter-sample peaks are detected. True-Peak lim-
iting handles these transient peaks seamlessly,
keeping your audio at its finest.
Pre Limit Gain section
Gain Trim parameter
Range: -18 to +18dB (Default: 0 dB)
Use the Gain Trim parameter to gain trim for the
left and right channels. This parameter can be
used for true-peak protected level conversion.
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.