Ensemble Designs 9670 Audio Automatic Gain and Loudness Control and 9690 Audio Compliance and Monitoring Software - Manual (Page 22)

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Avenue 9670 - page 22
LevelTrack™ Audio Loudness Control AGC Software Option
In the real world, content provided to a broadcaster doesn’t always contain a valid dialnorm value.
Much of the commercial content received at the local level contains none whatsoever. In such cases,
the target loudness value should be -24 LKFS (+/- 2dB). This equates to a dialnorm value of 24.
Broadcasters should be using a BS.1770 metering system to determine proper LKFS values, and all
content received needs to have the dialnorm embedded prior to AC-3 encoding.
Until the “ideal world” becomes a reality, it may be necessary to have a device that maintains audio
levels at a particular dialnorm value, particularly when using a fixed dialnorm metadata AC-3 encoder.
Enter the Ensemble Designs 9670 LevelTrack software key for the Avenue 9600, 9550, 7660 and 7555.
This software uses the BS.1770 loudness algorithm to set a specific LKFS value to be maintained by the
audio stream. As mentioned earlier, this translates directly to a dialnorm value.
Station output audio that is run through one of the Ensemble Designs products with the 9670
software key enabled, can be preset to a specific LKFS value before hitting the fixed dialnorm
metadata EC-3 encoder. As an example, if the encoder has been set for a fixed dialnorm of 24, the
9670 software would be set to -24 LKFS – in effect feeding the encoder an audio loudness dialnorm
equivalent of 24. This allows the broadcaster to use a lower cost encoder and still maintain consistent
loudness levels required by the Calm Act.
The FCC mentions that enforcement of the Calm Act will be complaint driven. If stations show a
consistent pattern of complaints related to audio level disparity, the FCC will investigate. This is
where the Ensemble Designs 9690 Audio Compliance and Monitoring software along with any of the
products mentioned earlier will provide a record of LKFS levels of up to four devices. This record can be
used to prove compliance.
By installing and properly setting up a 7555, 7660, 9550 or 9600 with 9670 software key for LKFS
AGC, and 9690 software key for compliance recording, broadcasters can rest assured that they are in
compliance with the Calm Act, and limit audio loudness complaints by their viewers. That’s a winwin.
Calm Act Update – NAB 2012: The word around NAB this year is that the ATSC A/85 committee will
reconvene shortly to make modifications to the A/85 Recommended Practice for Maintaining Audio
Loudness upon which the Calm Act is based.
Specifically, the committee is meeting to discuss standards for the use of “gating” in LKFS averaging.
This process removes audio below a certain threshold, from the LKFS averaging equation. They will be
meeting to determine exactly where and how the threshold will be implemented.
The problem with the existing spec is that silence is included in the LKFS averaging to determine
dialnorm. This means that if a broadcaster were to air a 30 second spot that is silent – (has no audio),
they are in effect, non-compliant with the CALM Act (+/- 2 dB from average). In addition, the silence
will effect the averaging after audio resumes causing a louder than normal perceived loudness until
proper averaging returns things to normal.
The committee will address these issues. It has an implication to broadcasters and manufacturers alike.
LKFS metering will have to take into account the threshold of the gating before determining overall
LKFS average. File based dialnorm solutions will have to rework their algorithms. Broadcasters of
course, will still have to be in compliance with the Calm Act. All of this has to be done by the December
of this year. Ensemble Designs will be keeping a close eye on these proceedings and will be looking to
make enhancements to our AGC and Compliance software to reflect changes to the spec. Stay tuned.