Download A/85:2013

ATSC A/85:2013
Establishing and Maintaining Audio Loudness, Annex H
12 March 2013
Annex H: Quick Reference Guide for Station and MVPD Engineers
Audio Loudness Management
H.1 INTRODUCTION
Note: This Quick Reference Guide is based on the ATSC Recommended Practice: “Techniques
for Establishing and Maintaining Audio Loudness for Digital Television,” A/85 (the “RP”), and
its full text is found as Annex H of the RP.
This Quick Reference Guide summarizes the recommendations in the RP and provides
guidance to broadcasters and other video program distributors on controlling and maintaining
consistent audio loudness of their TV stations and channels.
H.2 SCOPE
This Quick Reference Guide is not intended to replace the complete RP. Its scope is limited to a
‘how to’ guide for television station operators and MVPDs. Readers of this document are
encouraged to review the complete RP for more detailed information and the background to this
Guide. In the event of a conflict between the Guide and the RP, the RP takes priority over this
Quick Reference Guide.
This Quick Reference Guide is based on the use of a fixed metadata system10 (see Section 7.3
in the RP).
H.3 DEFINITIONS
Anchor Element – The perceptual loudness reference point or element around which other
elements are balanced in producing the final mix of the content, or that a reasonable viewer
would focus on when setting the volume control.
BS.1770 – Shorthand for ITU-R BS.1770 [3]. This specifies an algorithm that provides a numerical
value indicative of the perceived loudness of the content that is measured. Loudness meters
and measurement tools which have implemented the BS.1770 algorithm will report loudness
in units of “LKFS”.
Dialog Level – The loudness, in LKFS units, of the Anchor Element11.
dialnorm – An AC-3 metadata parameter, defined in A/52 [4], that is carried in the AC-3 bit stream.
This is used to indicate how far the average Dialog Level is below 0 LKFS. Valid values are 1
to 31. Loudness values outside this range cannot be expressed by dialnorm. The value of dialnorm
is numerically equal to the absolute value of the Dialog Level. The value of 0 is reserved.
LKFS – loudness, K-weighted, relative to full scale, measured with equipment that implements
the algorithm specified by BS.1770 [3]. A unit of LKFS is equivalent to a decibel.
Target Loudness – A specified value for the Anchor Element (i.e., Dialog Level), established to
facilitate content exchange from a supplier to an operator.
10
11
Agile metadata is an alternative to using the fixed metadata system approach. See Section 7.5
of the RP for details concerning the agile metadata approach.
The term “Dialog Level” is based on dialog’s widespread use as the anchor for mixing of
content and historically, it was felt that for most programs, dialog would be the Anchor
Element.
62