Dialling down dialnorm
Despite your best efforts and intentions, default volume control will never be consistent. One of the main culprits according Anthony Girmani, is dialnorm.
It’s one of the most common annoyances people experience with a home cinema sound system: they cue up a movie, set the volume to their normal level, hit play and yikes! It’s too loud! Or it’s too soft. It’s nowhere near the volume they thought it was going to be. But aren’t all films supposed to be mixed at reference level? Don’t these sound mixers know what they’re doing?
If you’re like me, you promise clients improved consistency in their experience through thoughtful engineering, installation and tuning. One benefit of that is supposed to be no more riding-the-volume-control syndrome. Despite your best efforts, your clients may encounter that problem anyway. In fact, they may already be having it and they’re annoyed; they just haven’t told you… yet.
This particular problem can have multiple causes, but I’m going to focus on just one. In my experience, this culprit trips up more people than any other. They don’t even know it exists, and it can cause large, apparently inexplicable differences in playback volume level.
The culprit is DialNorm.
Wait. What is that?
DialNorm is a ‘feature’ that Dolby included with Dolby Digital when it was chosen as the codec for digital TV transmission in the US. The concept was admirable. DialNorm was supposed to offer broadcasters the ability to balance the level of dialogue in commercials with the level of their main programming. Movies
or high quality episodic TV shows soundtracks are mixed with a wide dynamic range, with a good difference between average dialogue levels and peaks in the action scenes. Advertisements are mixed with dialogue loud up against the peak levels. If you match all the peak levels, that makes commercials seem really loud by comparison. The DialNorm feature is designed to automatically adjust the volume control so that as to maintain the proper dialogue level while compressing loud effects. Good plan, right?
Unfortunately, DialNorm relies a bit too much on the middle man (in this case mastering houses and TV audio production). In order for DialNorm to work properly, everything encoded in a Dolby format must first be run through a long term loudness averaging meter that, to quote Dolby, quantifies “the long-term
A-weighted average level of dialogue within a presentation, Leq(A)”. This is stated as a numerical value, in dB, between -1 and -31 (with -1 being a 1dB difference between peak level and average dialogue level (that’s very compressed) and -31 being a 31dB difference between peak level and average dialogue level).
In DialNorm standards, the maximum dynamic range is 31dB, for no volume control attenuation That number is input into the encoder and lives as a flag in the bitstream metadata. A DialNorm of 31 results in no attenuation of the Volume control. A DialNorm of 21 results in 10dB attenuation since it was detected
that the average dialogue level was 21dB below peak level, and therefore 10dB louder than a high dynamic range movie. Adialogue of 1 would results in 30dB attenuation, which is huge!
Zoom! Was that the sound of the previous paragraph flying over your head? If so, you aren’t alone. Long story short, basically no-one does the whole “run the presentation through the loudness meter” part and instead sets the DialNorm flag to… well, whatever the #&$! they want. So to speak, not literally. (Maybe literally.)
Anyway, you’re saying, “OK, Anthony, this is a lot of random technical speak, but what does it have to do with the whole volume control thing?”
The practical effect of DialNorm is that it turns the volume down. Plain and simple. Let’s say you start a movie and set the volume to reference level (0dB on the master volume) like you’re supposed to do. Unbeknown to you, someone who encoded it set a DialNorm value of -25dB, which means that the average
dialogue is 25dB below the peaks. That means, in reality, your volume control for DialNorm25 will be set to -6dB, not 0dB. DialNorm is controlling your volume without your knowledge or consent, and there’s nothing you can do about it. You can’t turn it off , and Dolby won’t let manufacturers disable it. According
to Dolby, it’s “perhaps the single most important metadata parameter”.
This all-important metadata parameter is being set by people who, by and large, don’t know or don’t care what they’re doing. Wow, I know that sounds harsh. And it’s not literally true, but it needs to be heard for effect. You may ask what evidence I have. Experience. I have looked at the DialNorm values on hundreds
(maybe thousands by now) of Dolby bitstreams across multiple formats, titles and providers. The DialNorm values are obviously inconsistent and illogical just looking at them – no high-tech averaging meter needed.
I have a little homework for you. Pick a mainstream movie. Get it on disc and rent or purchase it from all the major streaming providers available in your region. Next, make a little chart that lists the providers (including ‘disc’) on rows and DialNorm values in a column. Play the title from each provider, check the DialNorm value and write it down. How do you do this, you may ask? Many surround processors and receivers have a page buried somewhere deep in the OSD that lists audio bitstream parameters – including DialNorm when the bitstream is Dolby.In the case of Denon/Marantz products, it’s under the Setup/General/Information/Audio menu. It’s essential that you do this using a source device that outputs native Dolby bitstream, not decoded PCM or a live mixed Dolby bitstream done live by the product. (Unfortunately, this precludes iTunes as a provider because there’s no way to get native bitstream out of any device that will play iTunes movies. At least, there’s no way I know of. Extra bonus points to you if you can find one.) What you’re going to see are different DialNorm values for the same title from different streaming providers, and those values will also differ from what’s on the disc. In some cases, I’ve seen variations of 9dB. That’s huge!
Here in the US, I also see large differences between the DialNorm on 5.1 encoders vs. Dolby Atmos from streaming providers like VUDU. I know you guys don’t have VUDU in Australia, but if you have the chance to check 5.1 vs. Atmos on the same title from the same provider, do that as well. You’ll be shocked. Same movie. Same (basic) mix. Huge difference in DialNorm!
So what can you do about it? Well, nobody who’s reading this column can fix the problem at the source (mastering/encoding). You can call and complain but unless there’s major social networking outrage you’re not going to have any effect. If Dolby can’t get people to understand and use DialNorm properly, what
chance do we have? (By all means, launch a DialNorm reform Twitter campaign. It might work. Who knows?)
Hopefully, most of your customers will fall into the category of a simple solution. Are you ready for this? Just adjust the volume to your preference. Yeah, I know reference level and those numbers on the master volume control are supposed to mean something, but if they don’t anymore because of random DialNorm values, then, you know, kind of set it wherever…
You should definitely make sure the client understands that the problem exists on the content provider’s side, not the end user side. There’s nothing he or she or you can really do about it.
That being said, if you get the rare client who wants to go deeper, to really understand how to ‘correct’ the inconsistency, try this out.
First, make sure the system is calibrated to reference level. I’m going to assume you know how to do this or can find out. Basically -30dBFS = 75dB SPL main channel, 85dB SPL LFE channel. If you understood the previous sentence, I need say no more.
Second, tell the client to play a movie. It doesn’t matter if it’s a disc or streaming, but you still must use a device that outputs native bitstream. This means no Apple TV 4Ks. Yes, that’s right. I’m sorry (not really).
Third, tell the client to set the master volume where he or she normally listens. Let’s say that’s 15dB down from reference, signified by ‘-15dB’ on the master volume. Oh, and make sure the volume control is on relative scale (-80dB to +18dB) not 0-100 or some such.
Fourth, have the client navigate to the bitstream information screen in the surround processor OSD and identify the DialNorm off set. It can be expressed different ways, but it’s most commonly going to be a negative number between 0 and -30 (if it’s 0, the line for it may be left blank). For the sake of our example, let’s say the off set is -6dB.
Fifth, exit out of the menu and raise the master volume by the absolute value of the DialNorm off set (remove the negative sign). In our example, you would have the client raise the master volume 6dB from -15dB to -9dB.
Congratulations, you have removed the effect of DialNorm. It is essential that your client understands that the master volume is not really at -9dB. Dolby and the mastering house are stealthily (and perhaps unwittingly) lowering the volume an additional 6dB, so the effective volume really is -15dB. Nope, not confusing at all.
Couple of additional notes. A lot of people think mix levels are all over the place for movies, with some being really loud and some being really quiet. That does happen. Rarely. In my experience, wild swings in volume are 90% or more DialNorm’s fault and 10% or less mix level. Mixers work really hard to put out a good, consistent product and they get pretty sensitive when you start accusing them of not knowing how to mix at the right level.
Also, DTS tracks don’t have DialNorm. Years back DTS tried to emulate Dolby and added it as an option, but it never became a thing with DTS and is almost always off (no off set). I can recall a grand total of one DTS track that showed an off set. It was that awful live action G.I. Joe movie from a few years ago. Don’t ask me why I remember that!
Side note. Back in the ‘90s, on DVD, almost all major movie releases used DialNorm -27dB. (Urban legend is that this was due to a sincere but somewhat ill-advised ‘helpful hint’ from Dolby that the typical DialNorm value for a movie was around -27dB. Naturally, rather than actually measuring mixes using the averaging meter, everyone just set the DialNorm flag to -27dB.) A lot of these same releases also included a DTS track, which didn’t use DialNorm. If you compared the two with the same master volume setting, DTS would be 4dB louder. A slight increase in volume is interpreted by most people as an increase
in quality, so everybody thought DTS sounded better. It may have (it didn’t), but you’d never know unless you took out the DialNorm off set in the Dolby track! Fast forward 20 years and I see the same people claiming that the audio from one streaming provider is better than another – usually because the bitrate is
higher and that must mean the quality is higher. Guess what? DialNorm’s still @#$%^ing with their comparisons.
Finally, we have a bit of a reprieve from on high when it comes to Dolby Atmos/TrueHD tracks on 4K Ultra HD Blu-ray (and maybe Blu-ray; I haven’t looked at a Blu-ray Disc in years). All the ones I’ve looked at so far have DialNorm turned off (DialNorm -31dB or 0 off set). Maybe they’re finally learning? That’s not to say an odd track won’t pop up that uses some off set; you should still check every one to be sure. Once you dip your toes into streaming, though, all hell breaks loose.
Hopefully, I’ve helped you out in some way instead of ruining your day or just totally confusing you. I’m sorry I don’t have a better ‘solution’ to the problem (just set the bloody volume where you want and be done with it). I’ll leave you with a bit more homework, which is totally optional. Now that you know about DialNorm, why don’t you see if you can come up with some creative way I haven’t thought of to remove it from the equation, as far as your clients are concerned? You know, some invisible automation process behind the scenes that reads the DialNorm off set and automatically trims out the value. (Wow, I just thought about all the folks at Dolby that I just made furious by suggesting that. My response: guys, I’ve asked you about this in the past and gotten either no response or a restatement of what the encoding manual says. If you want to w rite a counter to what I’m saying, to explain how this madness is actually a relevant, well ordered process, I’ll be first in line to read and re-Tweet.)
If you come up with a really good idea, let us know! There are already some alternatives that attempt automatic volume levelling similar to DialNorm, except that they don’t require a bitstream flag. I’m not going to get into whether or not those are a good idea. This has specifically been about DialNorm. Can you believe no one ever talks about it? How did such a good intention go so far awry…