Dolby Encoding & Room Calibration

[Enos]

Hi guys!
I've just been reading all related posts regarding these subjects but can't find decent answers.I am primarily a sound designer/editor but time and again find myself dubbing (mixing) my material as well and encoding to AC3 for screening and so on. So here go the two questions:

1) Regarding room calibration, I understand the basic process and usually calibrate my room to reference level (-20dBFS) = 85 dBSPL for theatrical stuff and a bit lower (79-82dBSPL) than that if I'm mixing for TV or web release. However, I calibrate EACH channel (or speaker) to this level, as opposed to calibrating all speakers to the same level and then having the TOTAL output of all speakers calibrated to reference = 85dBSPL. So my question is, when calibrating, am I calibrating each channel/speaker to 85dBSPL (or whatever level I am calirbating to) or do I calibrate to that level with ALL channels on?



2) Now, regarding encoding your final mix to an AC3 file for DVD delivery. I keep getting my mixes a LOT quieter when encoded compared to my original levels in the room when mixing. I am setting dialnorm to -20 which is pretty much what I am mixing my normal level dialogue to and then setting my compression to Film Light Compression. So if I am mixing dialogue average levels to -20dBFS and set dialnorm to -20, the decoder will be lowering my mix by 11dB right? So what can be done or what should I be changing to get the levels louder on DVD?

[postprosound]

Yes, calibrate each channel to the reverence level. and just a note, don't forget that panning law thing, and make sure you are using mono tracks to a single output. I'm sure you know this; i just seem to forget this all the time. Also, i'd only use 85 if your room is rather large, like a dub stage. For smaller rooms, I'd lean more toward 82ish for film material.

2. Research a bit on dialnorm. Dialnorm does not refer to the number that you referenced to. (in your case, -20db) It's a number that is more of an average that is extrapolated by either the Dolby LM100 box, or the Dolby plugin. Simply, it measures the dialog only, nothing else, and then gives you a number that is the overall average of your dialog. Numbers in the -31 to -24 are often reported or asked for.
You are correct in saying that it will lower the overall volume of your material. This is because when you set a given number as a metadata flag in compressor or other program, you are in effect telling the DVD player, 'this is how loud my material is, please raise or lower the output when you play so that it is something the listener will expect.' in your case, saying that your material -20 is telling the DVD player it is very loud, and that it must lower the volume. So, if you mixed for TV material, try -27 when you encode, and -31 for film.

[Enos]

Thanks for those answers. Here is my additional quuestions/clarifications on what you mentioned:

Yes, calibrate each channel to the reverence level. and just a note, don't forget that panning law thing, and make sure you are using mono tracks to a single output. I'm sure you know this; i just seem to forget this all the time. Also, i'd only use 85 if your room is rather large, like a dub stage. For smaller rooms, I'd lean more toward 82ish for film material.

Ok great, I've been calibrating each channel (as opposed to total output of all) but had a friend recently say he thought it was too loud when calibrated like that and said he calibrated for the total output which left me unsure (as I did agree mixing to that reference was loud). However, your statement regarding calirbating a bit lower for smaller rooms makes sense and could explain that. I will calibrate to 82dBSPL or so. Thanks for that. I always run a mono track routed to one channel at a time. Regarding the panning law, how would I take that into account. Shouldn't I just be calibrating each speaker equally so that each speakers of the 5.1 setup outputs at the same level when measuring from the mixing position?

Dialnorm does not refer to the number that you referenced to. (in your case, -20db) It's a number that is more of an average that is extrapolated by either the Dolby LM100 box, or the Dolby plugin. Simply, it measures the dialog only, nothing else, and then gives you a number that is the overall average of your dialog. Numbers in the -31 to -24 are often reported or asked for.

Yes, I understand that, I have calibrated the room at -20dBFS = 85dBSPL but also happen to be mixing dialogue average to -20dBFS (might have casued a bit of confusion).

You are correct in saying that it will lower the overall volume of your material. This is because when you set a given number as a metadata flag in compressor or other program, you are in effect telling the DVD player, 'this is how loud my material is, please raise or lower the output when you play so that it is something the listener will expect.' in your case, saying that your material -20 is telling the DVD player it is very loud, and that it must lower the volume. So, if you mixed for TV material, try -27 when you encode, and -31 for film.

So if I want the DVD ac3 version to be as loud as possible, should I be setting dialnorm to -31 or -27 even if the dialogue is mixed louder at -20? I thought one couldn't fool the decoder like that? So does the decoder rely 100% on the dialnorm setting to calibrate its output? Also, what about the DRC settings...I am using film light compression...should I be going for something else and how exactly does this work then relatively to the dialnorm setting affecting DRC?

[hummer]

Originally Posted by Enos

Yes, I understand that, I have calibrated the room at -20dBFS = 85dBSPL but also happen to be mixing dialogue average to -20dBFS (might have casued a bit of confusion).

So if I want the DVD ac3 version to be as loud as possible, should I be setting dialnorm to -31 or -27 even if the dialogue is mixed louder at -20? I thought one couldn't fool the decoder like that? So does the decoder rely 100% on the dialnorm setting to calibrate its output? Also, what about the DRC settings...I am using film light compression...should I be going for something else and how exactly does this work then relatively to the dialnorm setting affecting DRC?

Nope, nope, you're still not getting it. No offense, but you need to do some reading and researching. RTFM, as they say.

In a long-winded nutshell, the dialnorm number that you set on the encoder reflects a SPECIAL sort of loudness measurement, which is based on an algorithm that measures loudness over X amount of time, and is also weighted in different ways, sometimes proprietary, as is the case for Dolby Dialogue Intelligence, etc. As of now, this algorithm used is ITU.1770, and is found in a select few metering products from Dolby, T.C. Electronic, and some others. The unit of measurement is LKFS. It is an updated version of the LEQ(m) algorithm, which is still found in a whole lot of Dolby LM100s, and is still acceptable. You can APPROXIMATE this measurement using the Digidesign Phase Scope by looking at the LEQ(a) meter with 10sec (?) integration time, IIRC. It's not gospel, but it will give you an idea of just how different this number can be from your -20 dBFS average.

Note: This has absolutely nothing to do with the loudness calibration of your room.

Now, when you encode your AC-3 for DVD, you'll report to the encoder (select from menu) the dialnorm number that you measured with the Dolby meter while mixing.

Here's what happens... The idea behind dialnorm is to produce uniform loudness in the final product/broadcast, even with mixes coming in at various loudness levels. Dialnorm is a scale factor, which aims for -31. So if you set the encoder to -31, no attenuation will occur. If you're following spec, this means that your dialogue levels were reading -31 on the LM100 while mixing, which is relatively quiet.

If you set dialnorm = -20 on the encoder (which I have never encountered, it's too loud) then your dialogue levels would need to be reading -20 on the LM100, again, if following Dolby spec. What happens then, is that the metadata accompanying the AC-3 will instruct the decoder to attenuate by 11 dB, bringing the level back down to the target of -31. Which is why your AC-3s were coming back quiet. Well, that and the fact that you enabled "Film Light" compression (most people don't), which is also going to change the dynamics of your mix. If you mixed with compression that you're happy with, why would you enable the Dolby compression?

There are no strict rules, such as -27 for TV, -31 for film. All situation are different. PBS requests -24, NBC wants -23, and a popular DVD authoring house that I've worked for wants -27.

Oh, and try 79 dB(C) SPL for near-field monitors.

[TVPostSound]

Yes, I understand that, I have calibrated the room at -20dBFS = 85dBSPL but also happen to be mixing dialogue average to -20dBFS (might have casued a bit of confusion).

How do you know you are mixing your dialog at -20 dialnorm??
Are you using a Dolby Media Meter Plug or LM100 to read the dialnorm??

Or are you mixing your dialogue "peaks" to -20 dBFS??? Which means you are probably around -30 dialnorm, and your encoding is compressing 10 dB.

If you are indeed mixing at -20 dialnorm, at 85 dBVU in your room, how does anyone stand to stay while you are mixing??
That is WAAAAYYY too loud.






.

[Enos]

The dialnorm number that you set on the encoder reflects a SPECIAL sort of loudness measurement, which is based on an algorithm that measures loudness over X amount of time, and is also weighted in different ways, sometimes proprietary, as is the case for Dolby Dialogue Intelligence, etc.

Note: This has absolutely nothing to do with the loudness calibration of your room.

Ok, I know that when calibrating the room you have to be using a special sort of loudness measurement sending pink noise to each speaker and aiming for 85dBSPL, C weighted, slow (according to Dolby instructions).

What I WAS getting wrong is finding the dialnorm level. I was simply using a rough dBFS value as the dialnorm level which was about -20 dBFS. I would need a decent Dolby metering plugin or something but will try using the Phasescope for now.

However, regarding the way dolby decoders react to the dialnorm metadata, is it possible to fool it? If my average dialogue is mixed to say -25 and I told the encoding process that dialnorm was -31, would it fool it and apply no level reduction resulting in a louder mix?

Well, that and the fact that you enabled "Film Light" compression (most people don't), which is also going to change the dynamics of your mix. If you mixed with compression that you're happy with, why would you enable the Dolby compression?

Film Light Compression relates to settings for DRC right? So if it is not active , which ideally it wouldn't, no compression would be applied to the mix. However, if it IS activated, at least the decoder will roughly know what kind of program material it has and can therefore apply a reasonable compression without overdoing it too much. I thought that is what those settings were all about.

If you are indeed mixing at -20 dialnorm, at 85 dBVU in your room, how does anyone stand to stay while you are mixing??
That is WAAAAYYY too loud.

Yep, I was not calculating the dialnorm correctly. I was simply setting dialnorm to whatever my dBFS was, in this case, average dialogue was between -24 to -20 with peaks as high as -6. So I will go and calculate the correct level with phase scope and try and get my hand on a dolby media meter plugin. Do the Neyrink plugins offer such level monitoring btw?

[Enos]

Ok, just gone and measured the level with Surroundscope (same as Phasescope basically) with LEQ(a) with 10seconds setting and the resulting value was bang on -31

So hopefully all I was doing wrong was setting the dialnorm level. I am bouncing a new version of the mix and will go and encode it into AC3 and test it out.

Thanks for the advice. Would still like to know your advice on my question in my post right above this one regarding DRC and settings for it (film light compression,etc...)

Thanks for all your help guys! This is why I usually recommend clients to get it mixed by mixers and not sound editors :p But thanks for helping out and hopefully I can get better results now!

[Enos]

Just finished monitoring my latest trial DVD after finding the "real" dialnorm using Surroundscope (which was spot on -31). Encoded that into an ac3 with dialnorm set at -31 and no compression and it sounds great. Nice, loud, dynamic and clean! Thanks a lot guys, I think I've got it now!

By the way, for a film going to DVD, we are burning to DVD Video which on the Compressor software I use limits the audio bitrate to 448 and only allows me to go higher than that if I select the setup as generic AC3. Does that mean that if I'm encoding sound with picture I can only go up to 448 and can only go higher if I'm burning say a Audio DVD?


Thanks for everything btw

[hummer]

Some may disagree with me, but I never, ever, use the Dolby compression.

I'm pretty sure 448 kbps is the max for the DVD spec.

Actually, for stereo, 192 kbps is the recommended data rate, but I always go with 384 if I can. Typically, the data rate of the audio is determined by the bandwidth needs of the video.

And yes, you can "fool" (/lie to) the encoder by selecting -31. It won't adjust the levels.

[Enos]

Thanks Hummer! I thought it was important to choose a Dolby compression preset for whenever the audience chose to activate DRC, the decoder could treat the program material as respectfully as possible, depending on the type of mix and dynamic range involved. But I will stick to choosing no compression if that is not really the case.

Regarding bandwidth, 448kbps seems the only one allowed when burning to DVD Video, but I will make some tests and see if a slightly higher bitrate is allowed whenever there is space. Anyone got an answer tot his? Is it possible to encode an AC3 file at a higher bitrate than 448 when going to DVD Video?

[Mr_Dress_Up]

Originally Posted by Enos

Is it possible to encode an AC3 file at a higher bitrate than 448 when going to DVD Video?

No, DVD specs allow for a maximum bitrate of 448 with Dolby Digital. Blu-Ray allows more than that (640 I believe).