TC Electronic DB4 MKII - Manual (Page 72)

ALC 5.1
68 DB4 / DB8 MKII Algorithms
Trim parameters are the perfect place to change
the Target Level for broadcast platforms that re-
quire a higher average than in the -24 to -22 LFS
range.
Limit Threshold
Sets the Limit Threshold for all limiters. The
limiters in ALC5.1 use true-peak detection as
per ITU-R BS.1770. True-peak detection makes
overload of downstream 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 always use a conservative
Limit Threshold, even in digital transmission. Re-
serve the top of the digital scale for occasional
peaks in wide dynamic range material (feature
films, wide dynamic range music), so don’t go
above -6 dBFS in HDTV for normal broadcast
programming. This way, down-mixing or bass
management at the consumer will also not gen-
erate unexpected distortion. See Fig 6, 9, 10 and
11.
The distance between the Target Level of the
ALC section and the Limit Threshold is an im-
portant audio quality defining factor. Though
you may be typically working with a distance of
10 dB in analog TV, consider widening this to
maybe 14 to 16 dB in DTV, see Fig 1. Widening
can be accomplished by moving down the Tar-
get Level and/or raising the Limit Threshold.
For instance, a Target Level of -20 LFS or -22
LFS with a Limit Threshold of -6 dBFS would
widen the dynamic range of DTV, while a Limit
Threshold of -9 or -10 dBFS could be kept on
the analog feed.
Limiter Link
The Limit Link settings define which limiters work
together.
– ALL: If a threshold is exceeded in any channel,
all channels are limited.
– LCR, LFE: If a threshold is exceeded in one of
the Main channels, all Main channels are lim-
ited. If the threshold is exceeded on the LFE
channel, LFE is limited independently.
– C, LR, LFE: If the threshold is exceeded in the
Center channel, only that channel is limited. If
the threshold is exceeded in one of the other
Main channels, all Main channels excluding
Center are limited. If the threshold is exceeded
on the LFE channel, only that channel is lim-
ited.
Fig 11
Loudness control allowing Boost.
In this illustration,
Target Level = -20 LFS,
Limit Threshold = -6 dBFS,
Max Boost = 6 dB
Freeze Level = -46 LFS (Target -26 dB)
Fig 10
Loudness control allowing both Boost and At-
tenuation. In this illustration,
Target Level = -20 LFS,
Limit Threshold = -6 dBFS,
Max Boost = 6 dB
Max Attenuation = 2 dB
Freeze Level = -46 LFS (Target -26 dB)