AC3 audio having different volume on different TVs?

[Ty Ford]

Hello Chris and welcome to the Cow Audio Forum.

Are the TVs hooked up to the same source?

Does you normal audio sound the same on both TVs?

Regards,

Ty Ford
Audio Forum Leader

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[Chris Heuer]

Hi! The TVs are all connected by the same model Digital cable box, but not the SAME box. I have checked this on several different tube and flat screen tvs.

Many flat screen owners say the ads are “blaring”. I have an older tv in my room an the audio sounds spot on perfect. I am trying to get a flat screen model to try in my room.

C

Chris Heuer
Freefall FX, LLC

[Jordan Wolf]

Hi Chris,

First, a question: when viewing program material (not commercials), is there still a disparity in levels between the two tv sets? If so, then you’re got a few more places to check.

Here are some options to explore:

1.Most set top boxes allow the user to select fixed volume (used when there’s a central receiver unit) or variable volume control (when the TV is already set). Take a look into the settings to see which is selected for each box.

2. All the “modern” televisions I know of allow for some adjustment of the volume and rudimentary EQ adjustment. Make sure these aren’t set to one extreme or the other. Also, realize that sometimes these settings are source-dependent and are independent of each other.

3. Try hooking up the CRT TV’s cable box to the “modern” TV and then vice-versa for that TV’s box (but only test them one at a time). If the issue transfers with the box, you know where the problem is. If it doesn’t, then you know it’s the TV.

One other point to consider is what connections are being used and how the signal gets into the TV, is processed, and gets to the speakers.

A number of things, I know, but I figured I would try to put them all on the table for you. Anyone else think of anything I missed?

Wolf
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[Chris Heuer]

Thanks Wolf. I am working on getting a flat screen in my room so I can test multiple monitors on one box. The loudness reports are coming from customers and some employees who are seeing the ads at home. I have visited a few and heard the problem. As well as searched their TV menus to see if there were any audio settings that may fix the issue.

The frustrating thing is, the relative volume of our inserted ads compared to the programming (cable shows) on the networks is different.

In my office, the ads are exactly the same level.
At the customer’s home, the ads on the same network are much louder.

There are, as you listed, a LOT of factors between the head end and that TV. I wondered if the reason the same ad on the same network having two different output levels might be because the file that is airing has more audio information/channels than some TVs (mine) can output.

Does that make any sense? Might Dolby files have that ability?

Thanks again for any input/wisdom!

Chris Heuer
Freefall FX, LLC

[Jean-christophe Boulay]

I think all the troubles are related to the Dialog Normalization (DialNorm) data point of the AC-3 mixes.

We’re in a bit of a transitional period with regards to broadcast digital audio right now with the imminent implementation of the CALM Act in the US. Broadcasters, set-top box manufacturers and TV manufacturers are all at a slightly different step of this process and the results can be quite unpredictable, as you’re learning. All the theory is laid out in this year’s most gripping thriller read, ATSC a/85 (https://www.atsc.org/cms/standards/a_85-2011a.pdf). It’s a boring but important read.

As Wikipedia will tell you, Dialnorm is the meta-data parameter that controls playback gain within an AC3 stream. Originally, you’re supposed to set it to the average dialog level of the encoded program, as read in dBFS. For commercials, that doesn’t work so the overall level in dB LKFS is the level used to set it. That is laid out in section 5 of ATSC a/85. At some point, you’ll need a metering solution to measure LKFS so might as well sort that now. The DialNorm value of the AC3 stream for a commercial should be the positive integer of its LKFS reading, as set out in section 4. If you do that, you should be good.

That doesn’t mean the whole chain will be good, not by a longshot. If the stream goes through broadcasters, they could have their servers and encoders set any number of ways depending on where they’re at in their infrastructure switch to digital. If the stream passes that step unharmed, it arrives at the set-top box. If that box will decode the AC3, its internal settings like Loudness, Late-Night Mode and Dynamics come into play. If the set-top box passes the AC3 to the TV, that could be decoding and applying its settings. Then again, maybe the TV passes the encoded stream to the main audio receiver or amplifier’s decoder, which would apply its settings.

So you never know what the broadcast chain is doing to your level, and there is any number of things the consumer’s system could be doing to the level, all based on that little metadata point that is DialNorm. You can’t make any relations between an AC3 stream that’s gone through broadcast and a consumer’s system and your original export in your room.

Right now, some broadcasters ask that you specify your DialNorm level during the ingest process, some require it to be a certain value, so you have to mix to that level from the get-go. The vast majority don’t even mention it and that’s where the problems start. If there is any way of providing straight PCM audio, that would probably be the most reliable now as the encoding and its effects are on the broadcaster or distribution service and you can wash your hands of it as long as you mixed to broadcast levels, which you are since older TVs that disregard metadata get the correct level.

So I’m quite sure DialNorm is what you need to look at, though the Channel Mode meta-data point could also affect level, so you should check that too. Read the boring technical papers ATSC A/85 and maybe ATSC A/53, measure your levels in LKFS, set the DialNorm accordingly and it’s out of your hands after that.

IHTH,

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

[Chris Heuer]

That sounds like the problem… just way more complicated than I was hoping for! I will read the link. Thanks so much!

Chris

Chris Heuer
Freefall FX, LLC

[Jean-christophe Boulay]

I may be making it sound more complicated than it is in practice with my usual focus on details. Once you grasp the concepts, the application is rather straightforward.

Good luck!

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

[Chris Heuer]

Yeah, I am outputting from Adobe Premiere without using the Surcode plug in. I’m not sure I have any way to control the DialNorm.

Chris

Chris Heuer
Freefall FX, LLC

[Chris Conlee]

[Chris Heuer] “I’m not sure I have any way to control the DialNorm.”

Do you have access to a Mac with Compressor? You can use that to encode your AC3s with proper DialNorm. However, as Jean-Christophe mentioned, you need to actually mix to the DialNorm, in order for it to work properly, then you need to hope that the rest of the chain is properly handling your stream.

Chris

[Chris Heuer]

Yeah. I am a Mac guy but have been migrating away from the entire Final Cut suite. I may have to use Compressor hearing that.

Dumb question (probably really dumb!). Wait, first a dumb statement! I am not sure how to mix to the DialNorm. I did download OrbanLoudnessMeter 2.0.3 to monitor my audio. Now for the dumb question.

Is simply dropping my master audio volume until it plays back at -24 LKFS the same as setting your audio to -24 LKFS when compressing it?

I am guessing NOT! 😉

C

Chris Heuer
Freefall FX, LLC