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Discussion Starter · #1 ·
I am curious about a couple of details in the way Dolby has implemented dialnorm. I hope someone knows why two particular numbers were chosen.


First, why was -31dBfs chosen as the proper level for average dialog?


Second, why do Dolby encoders have -27dBfs as the default dialnorm value? It looks like most movies are encoded using the -27 default, meaning the decoder will attenuate the output by 4db.


DTS-HD uses dialnorm, too. But, DTS encoders default to -31, meaning no attenuation of the final output. So, the same soundtrack encoded both ways will usually playback 4db lower in TrueHD than it will in dts-MA. That seems odd to me.


I understand that the default values can be changed by the person doing the encoding. But, it doesn't look like that happens very often.
 

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I have never understood the premise of dialnorm. I have seen both -2 db or -4 db displayed on my Onkyo AVR when playing a True HD BD. It also seems that I usually end up INCREASING the playback level of a DTS HD-MA BD by about 2 db over what I listen to True HD for the same apparent listening level in my room. That contradicts what you just said.
 

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Discussion Starter · #3 ·

Quote:
Originally Posted by bluesky636 /forum/post/17035191


I have never understood the premise of dialnorm. I have seen both -2 db or -4 db displayed on my Onkyo AVR when playing a True HD BD. It also seems that I usually end up INCREASING the playback level of a DTS HD-MA BD by about 2 db over what I listen to True HD for the same apparent listening level in my room. That contradicts what you just said.

The primary goal of dialnorm is to adjust output loudness so that average dialog is at the same level for all programs (-31dB below full scale). Full scale is 105dB. So, a DN of -27 means average dialog will playback at 78dB. -31 = 74dB and -21 = 84dB. If the dialog on a TV show was encoded at -21dBFS, then the decoder would lower the overall output volume by 10db so that dialog is output at -31. (Dialnorm is also used to set the "zero point" for dynamic range control.)


The decoding device executes dialnorm adjustments. With most decoders, when you see a DN adjustment of -2, that means the material was encoded with a DN of -29 and the decoder has attenuated it by another 2dB so that the output is -31.


Decoders never increase volume based on DN. They can only lower it. However, according to some reviews, it looks like Onkyo AVRs may intervene after the decoder gets done, increasing the volume back up to -27. Your experience that TrueHD tracks play louder than dts-MA tracks runs counter to the usual encoding values that are used with those codecs and to what most other people report. Most people say dts-MA is louder than TrueHD.


Meanwhile - does no one know the answers to my questions about why Dolby chose -31 as the proper level for dialog but set the default value of the encoder at -27?
 

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Quote:
Originally Posted by BIslander /forum/post/17023228


I am curious about a couple of details in the way Dolby has implemented dialnorm. I hope someone knows why two particular numbers were chosen.


First, why was -31dBfs chosen as the “proper” level for average dialog?


Second, why do Dolby encoders have -27dBfs as the default dialnorm value? It looks like most movies are encoded using the -27 default, meaning the decoder will attenuate the output by 4db.


DTS-HD uses dialnorm, too. But, DTS encoders default to -31, meaning no attenuation of the final output. So, the same soundtrack encoded both ways will usually playback 4db lower in TrueHD than it will in dts-MA. That seems odd to me.


I understand that the default values can be changed by the person doing the encoding. But, it doesn’t look like that happens very often.

-31dbfs is "proper" only in that it is the level in which the original signal is broadcast with no interaction from the system.


-27 is suggested as the default broadcast level so that most material will be attenuated but a perceived 4db increase in volume is still possible by attenuating less in order to properly match a broadcast level of -27.


It is all odd because no standards have been adopted and specified so there has been no widespread implementation and standardization.
 

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Quote:
Originally Posted by BIslander /forum/post/17035485


The primary goal of dialnorm is to adjust output loudness so that average dialog is at the same level for all programs (-31dB below full scale). Full scale is 105dB. So, a DN of -27 means average dialog will playback at 78dB. -31 = 74dB and -21 = 84dB. If the dialog on a TV show was encoded at -21dBFS, then the decoder would lower the overall output volume by 10db so that dialog is output at -31. (Dialnorm is also used to set the "zero point" for dynamic range control.)


The decoding device executes dialnorm adjustments. With most decoders, when you see a DN adjustment of -2, that means the material was encoded with a DN of -29 and the decoder has attenuated it by another 2dB so that the output is -31.


Decoders never increase volume based on DN. They can only lower it. However, according to some reviews, it looks like Onkyo AVRs may intervene after the decoder gets done, increasing the volume back up to -27. Your experience that TrueHD tracks play louder than dts-MA tracks runs counter to the usual encoding values that are used with those codecs and to what most other people report. Most people say dts-MA is louder than TrueHD.


Meanwhile - does no one know the answers to my questions about why Dolby chose -31 as the proper level for dialog but set the default value of the encoder at -27?

Makes sense.


My comment about True HD sounding louder is not based on any sort of measurement or anything. Like I said, it is an "apparent" difference. I mostly listen to DTS HD-MA BDs at -16 or -15 db below reference. True HD seems to be as loud at, say -18 to -16 db. The proof of the pudding is that the wifes yells at me to turn down True HD soundtracks more often then she does HD-MA soundtracks.



No, I don't know the answer to your question. Have you looked at the Dolby website? They have quite a few whitepapers on various subjects available to read.
 

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Discussion Starter · #6 ·

Quote:
Originally Posted by bluesky636 /forum/post/17035888


Have you looked at the Dolby website? They have quite a few whitepapers on various subjects available to read.

I've read through lots of the Dolby material and I can't find any explanations.
 

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Discussion Starter · #7 ·
Thanks. Perhaps I just don't understand your responses, but I don't see the answers to my questions.

Quote:
Originally Posted by Harrypt /forum/post/17035545


-31dbfs is "proper" only in that it is the level in which the original signal is broadcast with no interaction from the system.

I believe that's the case only because Dolby set -31dBFS as the proper output value. If Dolby had set -27, then that's the level that would produce no interaction from the system. So, why -31?

Quote:
-27 is suggested as the default broadcast level so that most material will be attenuated but a perceived 4db increase in volume is still possible by attenuating less in order to properly match a broadcast level of -27.

Sorry, but this answer lost me completely. The content producer is supposed to enter an accurate dialnorm value, one that represents the actual level of average dialog. Why have a default of -27? dts-HD encoders default to -31, which matches the output loudness of the decoder. That makes some sense. The -27 number doesn't, at least not to me. But, I have to believe there's a reason behind the selection of that particular number.
 

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Quote:
Originally Posted by BIslander /forum/post/17036034


I believe that's the case only because Dolby set -31dBFS as the proper output value. If Dolby had set -27, then that's the level that would produce no interaction from the system. So, why -31?

I'm not sure how to explain better. Dolby didn't set any proper output value. They merely developed a system capable inserting an attenuation value into the digital stream so that your decoder knows how many db to lower the volume. -31 is because the system is capable of a 30db attenuation so -31 is unity.

Quote:
Originally Posted by BIslander /forum/post/17036034


Sorry, but this answer lost me completely. The content producer is supposed to enter an accurate dialnorm value, one that represents the actual level of average dialog. Why have a default of -27? dts-HD encoders default to -31, which matches the output loudness of the decoder. That makes some sense. The -27 number doesn't, at least not to me. But, I have to believe there's a reason behind the selection of that particular number.

As I said, -27 is so that they can raise the volume 4db. This isn't quite how it works but think of it this way... the system is incapable of raising volume. But, if you set the standard of -27 you are lowering everything by 4db. Then if for some material is quiet, you could set to -29 and it will sound louder to the end user in relation to the norm.


There is no good answer to your question of why different formats are different. The answer is because the system has not been adopted and standardized.
 

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Quote:
Originally Posted by BIslander /forum/post/17035485


Meanwhile - does no one know the answers to my questions about why Dolby chose -31 as the proper level for dialog but set the default value of the encoder at -27?

Dolby has NOT set a "proper" level for dialogue. In TV, producers are free to place dialogue at whatever level they want to. They set dialnorm to indicate what the level of dialogue really is in their mix.


In order to avoid chaos with all of these potential dialogue levels, the DD system includes a way to "normalize' dialogue to a common level. As someone mentioned, normalization can only turn the level down. If it turned it up, something might clip downstream. The level that Dolby chose to turn the dialogue down to is -31. (This is why there is a 1-31 range in dialnorm values.) The DD decoder looks at the dialnorm number in order to figure out how much it has to reduce the level to put dialogue at -31. This -31 level exists only deep inside the DD decoder. The audio is processed by the rest of the receiver and the viewer sets the final dialogue loudness with the volume control.


The default value of -27 was chosen because motion pictures, with their tightly defined mixing room monitoring loudness, end up with dialogue at -27. That does NOT mean that all dialogue must be mixed at -27. It only means that the indicated dialogue level (the dialnorm value) must equal the actual measured dialogue level. The DD system will handle it from there and ensure consisten dialogue reproduction loudness.
 

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Discussion Starter · #11 ·

Quote:
Originally Posted by hphase /forum/post/17036827


Dolby has NOT set a "proper" level for dialogue. In TV, producers are free to place dialogue at whatever level they want to. They set dialnorm to indicate what the level of dialogue really is in their mix.

Yes. But, the key is what happens next. Dolby manages the loudness of the output so that dialog of all programs encoded with accurate DN values is at the same level, at -31dBFS. That means Dolby systems do not playback dialog where the producer placed it. They play it back at the level Dolby decided was "proper" for dialog. I'm not objecting to anything about that. But, I believe you have mischaracterized what dialnorm is designed to do.
Quote:
The level that Dolby chose to turn the dialogue down to is -31. (This is why there is a 1-31 range in dialnorm values.) The DD decoder looks at the dialnorm number in order to figure out how much it has to reduce the level to put dialogue at -31. This -31 level exists only deep inside the DD decoder.

Back to my question: why -31?
Quote:
The default value of -27 was chosen because motion pictures, with their tightly defined mixing room monitoring loudness, end up with dialogue at -27.

I've seen that said before, but I've never seen it sourced. (Actually the link from bluesky636 mentions that movie dialog is generally recorded at a level corresponding to -27 during encoding.) So, do you have any sourcing to link the Dolby -27 encoder default to film industry recording standards or practices?
 

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Discussion Starter · #13 ·

Quote:
Originally Posted by Harrypt /forum/post/17036264


I'm not sure how to explain better. Dolby didn't set any proper output value. They merely developed a system capable inserting an attenuation value into the digital stream so that your decoder knows how many db to lower the volume. -31 is because the system is capable of a 30db attenuation so -31 is unity.

OK. Whose "system" is Dolby using? Is this a standard somewhere? Or, is it something Dolby devised itself? If the latter, why the 30dB attenuation limit?

Quote:
As I said, -27 is so that they can raise the volume 4db. This isn't quite how it works but think of it this way... the system is incapable of raising volume. But, if you set the standard of -27 you are lowering everything by 4db. Then if for some material is quiet, you could set to -29 and it will sound louder to the end user in relation to the norm.

You're talking about cooking the books there, and I doubt that's Dolby's reason for using a -27 value as a default. Sony, for example, has decided to encode TrueHD tracks at -31, meaning its titles will playback louder even though they haven't been recorded louder. That's also what usually happens with dts-MA, where the encoder defaults to -31. Movies that should be attenuated by 4db are not because inaccurate DN values are entered by the content producers.
 

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I'm either misreading or misunderstanding here. If memory serves me right, -31 is used in film (movies) whilst -27 was typically used in broadcast applications due to more limited bandwidth. Not entirely accurate because a broadcast of a movie would also be -27.
 

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Quote:
Originally Posted by BIslander /forum/post/17037414


a)Yes. But, the key is what happens next. Dolby manages the loudness of the output so that dialog of all programs encoded with accurate DN values is at the same level, at -31dBFS. That means Dolby systems do not playback dialog where the producer placed it. They play it back at the level Dolby decided was "proper" for dialog. I'm not objecting to anything about that. But, I believe you have mischaracterized what dialnorm is designed to do.


b)Back to my question: why -31?


c)I've seen that said before, but I've never seen it sourced. (Actually the link from bluesky636 mentions that movie dialog is generally recorded at a level corresponding to -27 during encoding.) So, do you have any sourcing to link the Dolby -27 encoder default to film industry recording standards or practices?

a) Good point. Anyway, as I said, ulimately the viewer/listener decides how loud dialogue gets played, not the producer. Normalizing the dialogue at least makes all dialogue play at the *same* level for each film, without changing the volume for different films. If TV producers and/or networks got on the ball, it would work for TV shows, too.


b) Because -31 was the lowest they level that they would usually find dialogue in a professionally mixed program. And they seem to be right, judging from the last quote at the bottom.


c)See below

Quote:
Originally Posted by BIslander /forum/post/17037435


Thanks. I'd read that before. It's good stuff. And, it says movies typically have a dialog level of 27dB LAeq below maximum level. So, perhaps that's why Dolby encoders set the dialnorm default to -27.

Bingo! You've found the answer!

Quote:
Originally Posted by BIslander /forum/post/17037456


OK. Whose "system" is Dolby using? Is this a standard somewhere? Or, is it something Dolby devised itself? If the latter, why the 30dB attenuation limit?

Dolby devised it themselves. See b) above.

Quote:
Originally Posted by Dennis Erskine /forum/post/17037778


I'm either misreading or misunderstanding here. If memory serves me right, -31 is used in film (movies) whilst -27 was typically used in broadcast applications due to more limited bandwidth. Not entirely accurate because a broadcast of a movie would also be -27.

Incorrect. Films are usually at -27. TV shows are usually louder, and measure around -24. -31 is what Dolby thought would be the lowest "regular" dialogue (not whispering, which doesn't last for the whole film.) "Films" on TV would be at -27 if they didn't change the original film mix.
 

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If you restrict the Dialnorm discussion to DVD playback, the only reason Dialnorm is required for DVD DD material is that DRC requires a properly calibrated dialog level in order for DRC to work properly. Nothing more to it than that!
 

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Discussion Starter · #17 ·

Quote:
Originally Posted by Dennis Erskine /forum/post/17037778


I'm either misreading or misunderstanding here. If memory serves me right, -31 is used in film (movies) whilst -27 was typically used in broadcast applications due to more limited bandwidth. Not entirely accurate because a broadcast of a movie would also be -27.

According to document linked above by bluesky636, Dolby says movies are typically at -27 while dialog in broadcast sources is usually louder, at -17. And, of course, specific programs may vary considerably from those averages, which is the primary point of dialnorm in the first place.
 

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Discussion Starter · #18 ·

Quote:
Originally Posted by J_Palmer_Cass /forum/post/17038271


If you restrict the Dialnorm discussion to DVD playback, the only reason Dialnorm is required for DVD DD material is that DRC requires a properly calibrated dialog level in order for DRC to work properly. Nothing more to it than that!

That's not what I am asking about in this particular thread, however.
 

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Quote:
Originally Posted by BIslander /forum/post/17038274


According to document linked above by bluesky636, Dolby says movies are typically at -27 while dialog in broadcast sources is usually louder, at -17. And, of course, specific programs may vary considerably from those averages, which is the primary point of dialnorm in the first place.




DD Dialnorm values for movies released on DVD are all over the place. War of the Worlds uses a DN value of -23. The Dark Knight uses a DN value of -31. A lot of movies use a DN value of -27.



The following article discusses Dialnorm in more detail than I am willing to go into. Note that DD equipment used in movie theaters do not use Dialnorm.


Feature-article-Dialog-Normalization-link here



"Before we address some of the concerns people have, lets look at a few technical detials. When we speak of how loud sounds are in a Dolby Digital soundtrack, we express the loudest level as "0 dB" and the quietest as "-105 dB". The Dialnorm value expresses the level of dialogue as how much lower it is then the peak (0 dB). So a value of "-31" indicates a point 31 dB below the peak and, incidentally, is the value at which no volume adjustment is performed by your consumer decoder. A Dialnorm value of -27 would indicate to your decoder that the dialogue is at a point 27dB below the peak, or 4dB higher than a program with a Dialnorm value of -31. Your decoder would then turn things down by 4 dB. A Dialnorm value of -25 would call for a 6 dB reduction and so on. The -27 setting "fits" movie soundtracks perfectly in that it yields a very natural level for talking and is likely the most common for movies. For decades this has been the standard level for dialogue in motion picture soundtracks."
 
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