This topic is rarely touched on…Of late, I did some experiments on the Dolby Audio Post Processing on my Anthem MRX 1140 and I have come a different perspective and conclusion. So here I am, sharing my thoughts. Mind you that I will be referencing alot to Anthem since I am currently using it. But before that, let’s talk a little about Dialnorm aka Dialog Offset values. Dialnorm is the brainchild of Dolby Inc. Dialnorm shouldn’t even exist if you asked me since its roots can be traced way back to the DVD roots when Dolby Digital 5.1 bed layers. Back then, the transition from one source content to the other can result in uneven sound levels - e.g. content authored in 2 channels (stereo) vs multi-channel (5.1 / 7.1). The solution by Dolby is the Dialnorm where the studio will set an offset, typically at -27dbFS to ensure the SPL levels for movies with 5.1 / 7.1 bed layers can be played back at a level that does not require home consumer to rush for the remote control to turn up/down the volume when the movie starts. This is all good and dandy except it isn’t anymore. Dolby Digital 5.1/7.1 codecs back then are all lossy codecs which has a limited bitrate of around 384kbps for Dolby Digital while DTS core has a bitrate of around 1,536kbps. These days, Dolby Digital Plus lossy codecs has an enhanced bitrate of 640kbps and now now some of the streaming services like Netflix and Disney Plus has enhanced the bitrate to 768kbps which definitely makes the overall sound better with more dynamics.
Then Dolby came up with this Dynamic Range Compression or DRC for short. Later they came up with a better version of DRC called Dolby Volume where the goal is the same (to make the quieter scene sound louder and make louder scene quieter and still maintain a reasonable listening level for the type of content one is watching or listening). Dolby Volume algorithm is the perception of of how human listen to different content at different volume and try to analyse it to give the most appropriate sound level. This is abit different from the way DRC works. DRC focused on the highest and lowest note within a spectrum. According to Dolby, both can work in tandem but to me, there are one and the same. Maybe Dolby Volume is slightly more sophisticated than DRC but the vestige of DRC lingers even when Dolby tries to repackage Dolby Volume as something new.
Now back to Dialnorm, it only exist in lossy audio codec, hence it does not work its magic on lossless audio codecs like Dolby TrueHD or Dolby Atmos. DTS audio codecs will not be affected by Dialnorm. Because of Dialnorm, Dolby Digital lossy codecs and occasionally Dolby Atmos tracks (if not authored correctly by the sound engineers) takes on a bad rap for being the more “inferior” vis-a-viz its DTS counterpart.
For Anthem users, you will see this option in the Web UI called, " Dolby Audio Post Processing". This is a DRC in its basic form. It comes with Movie, Music and Night mode. The moment you see “Night” mode, one will immediately associate it with DRC. In Denon and Marantz, I recalled there is this setting called Loudness Management. This is akin to Anthem’s Dolby Audio Post Processing as it engages in DRC sorcery in some form.
When a movie sound track encoded in Dolby - e.g. DD+ with Dolby Atmos track or just DD+ lacks the dynamics and the much needed sound level, it is almost certain that Dialnorm is the culprit. To defeat Dialnorm, one just need to use a mediaInfo app to see what is the dialog offset value (usually -27dbFS) and then apply the same level to compensate. For instance, at -27dbFS, one will need to increase the Master Volume by 4dB relative to the normal listening level. There is no way to predict what is the correct master volume level to listen to since sound is very subjective. Some prefer to listen at -25dB while others prefer -20dB or -15dB. Those are acceptable range as far as home theatre is concerned. We are not talking about 0db Reference level which is way too loud for any normal listening at home.
The best way is to defeat the Dialnorm if you can but there are only a handful of AVR and Pre-pro that can do that, mostly D&M Amps and AVRs. For Anthem and most other brands, no luck! One way is to re-author the movie (.mkv or .mp4) to remove the Dialnorm and reset it to -31dbFS (no offset). This can be easily done by using MKVMerge utiltity (freeware). Here’s an example of how to remove the Dialnorm.
Using MKVMerge utiltiy to remove the Dialnorm
If you are an Anthem owner and lazy to re-author the movie, then you can choose “Movie” as the content under Dolby Audio Post Processing. This will work nicely provided the Dialnorm is at -27dbFS. what this mean is that Dolby Audio Post Processing is able to compensate and negate the effects of Dialnorm - i.e. defeat Dialnorm so that the playback volume at a designated master volume of your choice remains largely the same as if you were playing other movie content with TrueHD with Dolby Atmos or DTS HD Master audio codecs.
However this is NOT a case where you can set once and forget…the Dolby Audio Post Processing is not as sophisticated. The Dialnorm is the issue here. Dialnorm is added in at the encoding stage, meaning user or AV equipment might not have the setting to turn it off. As mentioned earlier, you either have the Denon or Marantz Amp or Pre-pro to defeat it totally or re-author the movie file to remove the Dialnorm. Dialnorm can be a friend provided the sound engineer knows what he/she is doing.
One example where the sound engineer clearly knows what he/she is doing is the movie, Wolf Man (2024). The Dialnorm for this movie when authored in a E-AC3 + Dolby Atmos track, it has a huge differential in Dialnorm in the upwards of -18dbFS. This is almost 13dB of difference, meaning you would have expected the overally sound level to drop very drastically considering such a big attenuation.
However this is not true. In fact, if we re-authored the tracks and “normalize” the Dialnorm to -31dbFS, then the sound level at your normal listening level will be extremely loud. This is one rare caseload that only came to light after I have experimented it.
Here are some examples of Dialnorm in some of the recent movies encoded in E-AC3 + Dolby Atmos. Noticed not all are using the default Dialnorm of -27dBFS.
Then why some TrueHD Dolby Atmos track sounded weak if there is no Dialnorm exist? This comes down to the original sound track, some movie sound tracks just comes with a poor source, thanks for the sound engineers. So remember, DO NOT label your sound system as “bad” just simply because you are using one movie for testing. Test a few more movies before coming to the conclusion whether the issue lies with your AV sound system or just a case of a bad source.
So at the end of the day, is Dialnorm, a friend or a foe? There is no one size fits all answer or solution to this issue since it depends on the original source. If the Dialnorm undergoes a strict Dolby standards, then even a -18dbFS (huge difference) like the Wolf Man (2024) will not matter at the end of the day but if every studio choose the path of least resistance - i.e. using the default -27dbFS for all Dialnorm, then turning on Dolby Audio Post Processing to get back the much needed boost in overall sound levels and dynamics may not be such a bad idea. Alternatively, you can be diligent to perform a check using the mediaInfo app and re-author the sound track to remove the Dialnorm altogether to enjoy better quality sound.
If you asked me, I would say Dolby should just do away with the antiquated Dialnorm for DD+ tracks and come up with a new standard that does not need to fall back on old algorithm. Unlike DTS, Dolby’s dabbling into so many media content - e.g. AC-4 codecs for broadcast services, I can appreciate the need for a DRC-like or equivalent feature to keep the sound level at a homogenous level acceptable for home entertainment system.