CALM act for non AC-3 decoders???

[adru]

Okay... I've been snooping around the CALM act, BS1770, ATSC a/85 etc, and from what i've understood:

In ac-3 systems it is mandatory that

1. we include the dialnorm parameter
2. the dialnorm parameter truly represents the loudness of the material and is not some random value
3. at the decoder at the consumer appliance, suitable attenuation is done so that the final dialogue is produced at -31LKFS

I have a few questions:
1) How exactly is dialnorm measured? Do we measure the clip using the BS 1770 algorithm and just set the dialnorm value as the integrated loudness?
2) How do we rectify the problem for systems not using the AC-3 encoder-decoder set-up?
3) Is the following right?: In case of AC-3 systems, we measure the actual loudness, and in case there is a disparity between the measured loudness and the obtained metadata(for dialnorm), we set the actual(measured) loudness as the metadata for all transmission downstream?

Thanks guys.
Adru

[cananball]

In the US , ac3 is the standard for digital television audio distribution. Every set top box has an ac3 decoder in it to decode the ac3 and folddown to the stereo output. If you want to output 5.1 you need to use your own decoder via spdif.


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[nucelar]

Hi
To get an understanding on how the broadcast chain works, and how loudness and metadata fit in, I recommend reading EBU tech Doc 3344.http://tech.ebu.ch/docs/tech/tech3344.pdf
which goes into great detail. Some things may be EU centric, but most of it is generic.

Trying to answer your questions:
1. Dialnorm should be measured with an A/85 or R-128 compliant meter (they are both based on ITU-R BS.1770-2). The integrated Loudness is your dialnorm. 'Dialnorm' in this context is really a misnomer because dolby took dialogue as the anchor for the measurement but this is not the case for BS.1770., but the term reamins, as it is part of dolby ac3 nomenclature.
2. Non-ac-3 content. this is difficult. A current set top box can virtually play back any codec or lossless format. Loudness therefore is uncontrollable. In the broadcast environment though , it is recommended (hopefully mandated) that the source audio is normalized to -23 LUFS.
3. How the metadata is managed downstream, I have no idea, and it scares me. The EBU system is based on a normalized loudness at the source level. If the metadata is correct, it's a bonus, but the system can not rely on metadata.
Cheers

[adru]

Thanks guys