Algorithm Manual Revision 4
Table Of Contents
ALC 6
English Manual – Updated 2018-02-28 167
ALC 6
ALC6 is an automatic loudness adjustment pro-
cessor for mono, stereo, LtRt and 5.1 formats.
It is a further refinement of the predecessor,
ALC5.1, and available free of charge to users of
DB4, DB8, DB4 MKII and DB8 MKII.
ALC6 is primarily designed for broadcast ingest,
linking and transmission, but it may be used as
a safety belt in production and in live production
as well.
Introduction
More than a decade of research and standard-
ization work on loudness and true-peak level
has led TC to design high resolution, low latency
loudness processors such as ALC6.
ALC6 is part of a new transparent audio loop
spanning from production over transmission to
the consumer. With production rooted in loud-
ness-based metering, less processing is needed
at later stages of the distribution chain.
Furthermore, previous stages of the chain can
be reviewed and optimized by utilizing the same
loudness measure for logging purposes: A
closed loop based on open standards, all rooted
in ITU-R BS.1770.
Welcome to a new world of leveling, where dis-
torted and annoyingly loud audio belongs to the
past, and where programs of different genres
may be broadcast back to back without abrupt
level changes.
Automatic Loudness Correction
for Mono, Stereo and 5.1
ALC6 offers processing complementary to ITU-
R BS.1770, including derived standards used in
Brazil, China, Europe, Japan and United States.
ALC6 may fully or partly correct level jumps
within broadcast programs and at transitions
between them. The resolution is sufficiently high
to allow for cascades of more than one hundred
processors without degradation of sound qual-
ity.
ALC6 can be used to control level and improve
sound, not only in MPEG AAC or Dolby® AC3
based transmission and linking, but also on oth-
er broadcast platforms, such as analog TV, mo-
bile TV and IPTV.
ALC6 even makes life with AC3 easier for the
broadcaster by
1. limiting the amount of work and equipment
put into metadata handling,
2. enabling fixed Dialnorm transmission,
thereby also making the end-listener expe-
rience more predictable,
3. improving the overall DTV sound quality by
protecting the codec from downmix clip-
ping, and
4. reducing audio delay in the end-to-end sys-
tem.
Features
►
Low latency, high resolution audio processor
for mono, stereo and 5.1 formats
►
Loudness and True-peak adjustment adhering
to ITU-R BS.1770
►
Novel downmix Target processing for opti-
mized delivery to mono and stereo listeners
►
Novel Stridency Reduction parameter
►
Novel Normalized/Not Normalized parameter
to signal condition of input program
►
Novel True-peak limiter Profile for optimized
AC3 delivery
ALC6 Presets
ALC6 presets are found in the “Loudness, Multi-
channel” Engine Factory Bank.
►
Presets that have “Limit” in their name per-
form only negative loudness and peak level
correction.
►
Presets that have “Correction” in their name
are able to perform both positive and negative
gain correction.
Two ALC6 processors may be loaded in DB4,
while DB8 accommodates up to four processors.
The basic latency of ALC6 AES/EBU I/O is 0.8
ms, and processing is performed at 48 bit reso-
lution.