How to make your loudness comply
Jan 1, 2010 12:00 PM, Tim Carroll
With or without additional government regulations, ATSC standards published back in the mid-1990s and adopted as the law by the FCC mandate that loudness be correct. If you didn't know that, you are not alone. There is no practical guidance as to how to make this happen. However, a new ATSC recommended practice attempts to distill a lot of information into one reference.
ATSC A/85 “Techniques for establishing and maintaining audio loudness for DTV” lays out a comprehensive plan for managing loudness from production to transmission. Essentially, it boils down to measuring content using an ITU-R BS.1770-compliant loudness meter to ensure that all audio either matches a loudness reference (-24 LKFS +/-2 ) or that the audio and corresponding metadata match. In either case, content that does not match can be rejected or adjusted, or metadata can be reauthored.
Guidance on both permanent and reversible dynamic range control is presented to help broadcasters understand the choices, and practical advice is given for setting monitor levels properly in production and post production so that an appropriate dynamic range will result during mixing and not be relegated to arbitrary adjustment later. A useful quick start guide is included to point readers directly to areas of interest.
What does a broadcaster need from the station side? At a minimum, you need a copy of A/85 and at least one real-time ITU-R BS.1770-compliant loudness meter to act as the station's DTV audio “mod monitor.” It may be wise to invest in more than one to allow monitoring of incoming content and to keep live productions in check. There's no need for mixers to worry; loudness meters work alongside the existing devices they are comfortable with.
Since the overwhelming passage of A/85 in November, broadcasters now have a reference to point to in their own delivery specifications and can send a clear and united message to program and commercial providers that they require loudness consistency in order to preserve audio quality, maintain legal compliance and most importantly satisfy viewers.
ATSC A/85 can be downloaded online at www.atsc.org/standards/practices.php.
Tim Carroll is the president and founder of Linear Acoustic.
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