DialNorm and audio levels

[André Engelhardt]

Interesting read, thanks for posting Sir!

—
Audio Engineer, Sound Designer
Video- and Photographer
http://www.andreengelhardt.net

[Jean-christophe Boulay]

On this same subject, the ATSC has just published a new version of its CALM recommended practices. Most of the document is the same but there are additional annexes relating to techniques to be used on non-AC3-coded signals, so bypassing the standard LM100-DialNorm workflow. Basically, we fall back to a broadcaster’s LKFS norms in that situation.

Of course, it’s rather dry and techy but important reading for anyone who’ll be producing broadcast audio in the next few years. Pass the word.

https://www.atsc.org/cms/standards/a_85-2011a.pdf

JC Boulay
Technical Director
Audio Z
Montreal, Canada
http://www.audioz.com

[Ty Ford]

JC,

Thanks, as always, for tossing in.

Can you expound on LKFS?

Regards,

Ty

Cow Audio Forum Leader
Want better production audio?: Ty Ford’s Audio Bootcamp Field Guide

[Jean-christophe Boulay]

Hi Ty,

LKFS is a newer level measurement measure. It’s “Loudness, K-Weighed, relative to Full Scale”. The process takes all the channels of your multichannel audio signal, dumps the LFE, applies a filter to all channels (the K-Filter, which mostly cuts some low end and boosts about 2dB above 4kHz), measures the average power (Leq) and sums the channels back up, with some weighing. The surrounds are boosted 1.5dB before summing, for example. All this process is done within the metering tool as long as it conforms to the ITU-R BS.1770 standard. The measure is in decibels, but is reported as LKFS alone, not dB LKFS. I know TC Electronics have updated their metering tools with this algorythm. I like AudioLeak for its simplicity (https://www.channld.com/audioleak/).

I haven’t seen a spec sheet with LKFS on it yet, but some contacts at local broadcasters say that shouldn’t be too long, especially in the US where this will become the law by december. We’ll probably have to specify Dialog Level when delivering broadcast audio, so the DialNorm can be set accordingly by the operator. Either that or we’ll receive precise Dialog Level specs to respect. Because of the dumping of the LFE and the filtering and weighing, LKFS is really hard to guess based on more traditional measurements. You really have to measure it, which probably means new tools. And we all know how exciting it is to invest in metering! Clients go crazy for that stuff.

IHTH,

JC Boulay
Technical Director
Audio Z
Montreal, Canada
http://www.audioz.com

[Ann Clark]

JC,

I just got a spec for commercial audio levels from DirecTV: “Average audio levels shall be -24LKFS +/- 2dB”.

Since I’m working with FCP7, I don’t have a meter that addresses LKFS. How would I determine if my audio levels will work? The peak on the commercial is around -6dB according to the FCP meters. This has worked well in the past. Shall I roll off a bunch of tapes and chance it, or has DirecTV gone off the deep end with a new standard?

Your quick thoughts would be very helpful.

MacPro 2 x 2.8 GHz Quad-Core Intel Xeon 14GB memory – OSX10.6.4 FCP7

[Ty Ford]

Hello Ann and welcome to the Cow Audio Forum.

Lets see what others say, but……. After I read an article that tried to explain the system, I was left with more questions than when I started. It was like the statisticians had escaped from the computer farm and accidentally ended up on the audio farm…and I’ve been doing this a while.

At the end, someone popped in and said, peaks no higher than -6 dB and don’t let it get too quiet either, so watch the peaks and use a little compression and/or limiting. Without the Dolby plugin or hardware, “knowing” is still debatable due to the convoluted method of their calculations.

I’d say do your best with the -6 dB peak, push up the low stuff a bit still making it sound good and send it in to see what they say. Oh, and then let us know what happened.

Regards,

Ty Ford

Cow Audio Forum Leader
Want better production audio?: Ty Ford’s Audio Bootcamp Field Guide

[Ann Clark]

Ty,

Thanks for the advice. I’ll be sure the peaks stay within the -6 range and slap a Compressor/Limiter on it. I only saw one peak that went over the -6dB mark, so maybe I’m okay once I add the C/L filter.

As for sending it in to see what they say, I have two choices — the audio is right, or it’s right. If it is not right, let the yelling begin. ;-o

In Space Race parlance, this is an “all-up-test” — because of media and shipping costs, I get just the one chance to make a Beta SP tape, ship it in, and hope DirecTV doesn’t have a problem with it. I also have to send another copy of the tape directly to the client at the same time, so if it’s wrong, it’s wrong twice. Yipes.

Often, if these things are wrong, the net tells the client before telling us here, and it’s just a big, messy blowout over some smallish technical details that would otherwise be easy to fix.

I’m just trying to keep the yelling down, as well as tape costs, by being proactive, here.

I’ll keep you in the loop as to how this goes.

🙂

MacPro 2 x 2.8 GHz Quad-Core Intel Xeon 14GB memory – OSX10.6.4 FCP7

[Ty Ford]

Back at you, Ann.

Thanks for your sense of humor.

There are more and more facilities who have purchased the Dolby LM100 for over $3000.
https://www.dolby.com/professional/solutions/broadcast/loudness.html

There’s also the Media Producer Suite for about $4k.
https://www.dolby.com/professional/products/pro-audio/mastering-dvd-hd/dolby-media-producer.html

If you could find such a facility near you or buy what you need, you can run the show and feel more secure in your deliverables. Otherwise, you’re sort of stuck with that uncertain feeling and the advice of someone who only has half a clue.

IMO, audio shouldn’t be this big of a problem, but then audio level disparities are at criminally wild levels because broadcasters haven’t, for years, wanted to hire audio techs to sit at master control and ride gain. In the end, this loudness issue is a personnel issue. Broadcasters have simply abandoned what used to be their responsibility.

Regards,

Ty Ford

Cow Audio Forum Leader
Want better production audio?: Ty Ford’s Audio Bootcamp Field Guide

[Ty Ford]

from a friend…

“A reliable workaround is included in every copy of Pro Tools. I have been using it successfully for 4 years. It is the LEQ A analyzer in PhaseScope. Mix for an average reading that is 3 dB softer than the LEQ A analyzer (because of a difference in meter ballistics between LM100 and PhaseScope. Put the PhaseScope analyzer on 2 second sampling while you are mixing and try to keep the reading predominantly at the desired dialnorm spec. On final playack of the completed mix, set sample time to infinite. You should get a reading that is 3 dB quieter than the LM100 spec. Your mix will pass QC. ”

Cow Audio Forum Leader
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[Ty Ford]

“Sorry, I meant to say mix for an LEQ A reading that is 3 dB softer than the LM 100 dialnorm spec. Darned chopsticks!”

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