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.

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. :confused:

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. :confused: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?

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.

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. :D

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.

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.

Thanks. Perhaps I just don't understand your responses, but I don't see the answers to my questions.

-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?

-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.

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.

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.

BIslander:

Take a look at this document:

http://www.dolby.com/uploadedFiles/zz-_Shared_Assets/English_PDFs/Professional/32_JRiedmiller_NCTA2001.pdf

Particularly pages 1 through 6.

A search on "dialog normalization" on the Dolby site came up with 18 documents. This was the first.

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.

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.
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?
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?

Take a look at this document:

http://www.dolby.com/uploadedFiles/zz-_Shared_Assets/English_PDFs/Professional/32_JRiedmiller_NCTA2001.pdf
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.

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?

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.

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.

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

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!

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.

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.

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!

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.

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.

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 (http://www.hometheaterhifi.com/volume_7_2/feature-article-dialog-normalization-6-2000.html)


"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."

Thanks, BI...I have a 3" ring binder full of Dolby tech papers ... I will go back and read them again. Hate getting older...memory fades. :)

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.One would expect DN values to vary because the loudness of dialog varies from program to program.

The following article discusses Dialnorm in more detail than I am willing to go into.I am familiar with that article. But, it does not answer the two questions I have asked. I hope we can keep this thread focused on those specific dialnorm issues.

The article says -27 is often an appropriate input value for movies since that's how they tend to be mixed. But, is that why Dolby encoders default to -27?

Bingo! You've found the answer!
Maybe. Maybe not. That answer makes sense. But, I am hoping to hear from someone with actual knowledge here, not just a logical inference.

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.
Back to my question: why -31?
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?

Dialnorm does not and cannot change the level of dialog in the movie so that it is at -31dBFS. What it can do is to set the overall program level so that the average dialog is the same volume as the average dialog in a movie where the dialog averages -31dB. Why that number? Well, if you are going to normalize the dialog levels to some number, you have to have a number to use. I don't think Dolby has described in any great detail the reasons for its choices, but it seems in gneneral pretty obvious that Dolby thinks that dialog is normally at about -27dBFS, and that it needed to allow at least a little room to deal with movies that are even quieter.

So it creates confusion and/or complication if you want to play your movies at "real" reference levels. But that would happen with any system that attempted to do what Dialnorm attempts to do. Whether Dolby was wise to try is clearly open to debate. But if you are going to do it, you have to use hard numbers, and you would pick numbers that seemed to work for at least the vast majority of commercial releases. I think that's all they did, but I doubt you'll find an explicit statment one way or the other of an exact reason why DOlby chose -31 as the "quietest" dialog level.

Dialnorm does not and cannot change the level of dialog in the movie so that it is at -31dBFS. What it can do is to set the overall program level so that the average dialog is the same volume as the average dialog in a movie where the dialog averages -31dB.Yes, yes, yes. Dialnorm adjusts overall loudness, not any specific channel. The level of average dialog entered by the person doing the encoding is used as the reference point for making the adjustments.

Why that number? Well, if you are going to normalize the dialog levels to some number, you have to have a number to use. I don't think Dolby has described in any great detail the reasons for its choices, but it seems in gneneral pretty obvious that Dolby thinks that dialog is normally at about -27dBFS, and that it needed to allow at least a little room to deal with movies that are even quieter. Yes again. All quite logical and it could well be the answer to the question.

I doubt you'll find an explicit statment one way or the other of an exact reason why DOlby chose -31 as the "quietest" dialog level.So far that is certainly the case.

By way of providing some context to my questions, there's been extensive discussion of dialnorm in the forum at blu-ray.com. I offered the opinion that's been expressed here - that the Dolby -27 default probably comes from the level that dialog is usually recorded on films. Here's the exchange with Sir Terrence, a film industry "insider" who posts on that site:

The mastering process is not really related to the encoding process that tight. Dialog levels should be -12 average before the mastering process. That is for proper playback. That has nothing to do with the encoder/decoder values that are entered during the encoding process. Two separate processes

I am asking if anyone knows why Dolby chose -27 as the default. It could have been -31 or -25 or any other number between -1 and -31. Does -27 correspond to the level at which average dialog is normally recorded. In other words, was it chosen because it's a good default number? Or, is it just a number?


Personally I believe that -27 default is just a random position as to keep the audio consistent over all Dolby encoded signals.

I think Sir Terrence is a professional audio mixer. No one else at blu-ray.com stepped up with additional technical information on the subject. So, I decided to post my questions here at AVS.

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!
The DD system used in DVDs is identical to the DD ssytem used in digital broadcasting.

Your generalization borders on reckless and dangerous.

The article says -27 is often an appropriate input value for movies since that's how they tend to be mixed. But, is that why Dolby encoders default to -27?
Yes, yes, a thousand time, YES!

Maybe. Maybe not. That answer makes sense. But, I am hoping to hear from someone with actual knowledge here, not just a logical inference.
Do you need to hear it from Ray Dolby himself? If that is what Dolby says in their white papers, that's good enough for me.

I think that's all they did, but I doubt you'll find an explicit statment one way or the other of an exact reason why DOlby chose -31 as the "quietest" dialog level.
Per the ATSC documents, Dialnorm is an unsigned 5-bit number. 5 bits = 32 possible values. These values are 1 to 31, the value zero is reserved (and is not allowed to be used in encoders.)

I think Sir Terrence is a professional audio mixer. No one else at blu-ray.com stepped up with additional technical information on the subject. So, I decided to post my questions here at AVS.
If Sir Terrence is an audio mixer, he does not have to be well versed in the encoding process. (Judging from his post, that seems to be the case, and that's not a knock on the mixer.) Mastering a disc involves many processes, including taking the encoded audio and video and creating a complete file structure for creating a Blu-ray disc.

True, they are different processes, but the audio must be encoded properly, and mixers don't usually need to be aware of these things. The video encoding may make use of a "compressionist," but the Director of Photography doesn't usuall get involed in this.

Do you need to hear it from Ray Dolby himself? If that is what Dolby says in their white papers, that's good enough for me.And what exactly does Dolby say in its white papers? Perhaps you can point to the passages where someone at Dolby explains (A) why -31 is the level for decoder output and (B) why -27 is the default level for the encoder.

Sorry, but I am looking for something more substantial than you have provided so far.

The DD system used in DVDs is identical to the DD ssytem used in digital broadcasting.

Your generalization borders on reckless and dangerous.



What "reckless and dangerous" generalization? Obviously the DD system used in broadcasting uses a dialnorm value. So what? I clearly restricted my comment to the audio track in a DD DVD.

The simple fact is Dialnorm is not needed in any DVD other than to provide the reference audio level that is required by DD Dynamic Range Control.

Note that DTS DVDs do not use Dialnorm and they sound just fine.

And what exactly does Dolby say in its white papers? Perhaps you can point to the passages where someone at Dolby explains (A) why -31 is the level for decoder output and (B) why -27 is the default level for the encoder.

Sorry, but I am looking for something more substantial than you have provided so far.




What is the problem? The use of the word "default"? My receiver defaults to a volume level of minus infinity when I do a system reset. I simply set the volume to the correct level when I use it. Do you need to have an engineer from Sony produce a design study for you on how they came up with a default master volume level of minus infinity?

Someone had to select a default value in the encoder when they designed the unit, and they simply chose to start with the dialnorm value that will most likely be used in the encoding process. The end user of the encoder still has to select the correct dialnorm value for the content in question, so the default value will more times than not be the correct DN value.

What is the problem? The use of the word "default"? My receiver defaults to a volume level of minus infinity when I do a system reset. I simply set the volume to the correct level when I use it. Do you need to have an engineer from Sony produce a design study for you on how they came up with a default master volume level of minus infinity?

Someone had to select a default value in the encoder when they designed the unit, and they simply chose to start with the dialnorm value that will most likely be used in the encoding process. The end user of the encoder still has to select the correct dialnorm value for the content in question, so the default value will more times than not be the correct DN value.
Dolby gets trashed by a vocal minority because of dialnorm. Most of that criticism is tied to the 4db attenuation associated with the mismatch between the decoder's -31dB output and the encoder's -27dB default input. And, it's not just end users. Sony Pictures has started entering -31 during encoding to prevent output attenuation, even though the loudness of average dialog on its films has not changed to a quieter level.

That's the problem, which I mentioned at the end of my first post. While the person doing the encoding should enter a proper DN value, many merely accept the default. As a result, the same movie will often playback 4dB quieter using TrueHD than it will using PCM or dts-MA.

As for the statement I bolded above in your post, is that just your supposition or can you source it? btw, -27 is the most likely level for movies. But, what about TV shows, where the typical level of dialog is -17dBFS? And, of course, DTS made a different design decision, putting its encoder default at -31.

The simple fact is Dialnorm is not needed in any DVD other than to provide the reference audio level that is required by DD Dynamic Range Control.What gives that idea? There's no difference with how Dolby uses dialnorm on DVD, BD, or broadcast. In all cases, the DN value is used to adjust both output loudness and to set the proper compression point for dynamic range control. Loudness control over all program sources, including DVD, is the primary goal of dialog normalization.

Note that DTS DVDs do not use Dialnorm and they sound just fine.dts-HD encoders use dialnorm now and dts-HD decoders are set to attenuate dialog loudness to -31dBFS, just like Dolby.

What gives that idea? There's no difference with how Dolby uses dialnorm on DVD, BD, or broadcast. In all cases, the DN value is used to adjust both output loudness and to set the proper compression point for dynamic range control. Loudness control over all program sources, including DVD, is the primary goal of dialog normalization.




In a broadcast situation, there are hundreds and hundreds of different content providers used per day. Dialnorm (if properly applied) will allow the end user to listen to all progarm material at one master volume setting.


With a DVD, there is only one program. Do you need dialnorm to set the volume for different programs? No. Set the master volume once and you are done.






dts-HD encoders use dialnorm now and dts-HD decoders are set to attenuate dialog loudness to -31dBFS, just like Dolby.





DTS has always had Dialnorm and DRC in the DTS specification. They decided not to use it for DVD production. As far as "dts-HD decoders are set to attenuate dialog loudness to -31dBFS", that shows you do not understand what you are talking about.

Simply put, dialog can be recorded at any random dB FS level. That is up to the sound mixer. The encoder and decoder work together in that a -31 dB FS level that was encoded at -31 dB FS will be decoded at a -31 dB FS level. Dialnorm changes none of that.

What Dialnorm does is decrease the volume level of the entire output by the difference between the standard -31 Dialnorm value and the chosen Dialnorm value. Nothing is attenuated if a dialnorm value of -31 is used.

Perhaps DTS does now use Dialnorm, but does any specific DTS-HD content use a Dialnorm value other than -31 (AKA no volume reduction)?

In a broadcast situation, there are hundreds and hundreds of different content providers used per day. Dialnorm (if properly applied) will allow the end user to listen to all progarm material at one master volume setting.


With a DVD, there is only one program. Do you need dialnorm to set the volume for different programs? No. Set the master volume once and you are done.Most people use the same sound equipment for TV and disc playback. When properly implemented, dialnorm allows us to watch all such sources without needing to ride audio levels. But, since you apparently only have one DVD that you ever watch, I guess this doesn't apply to you. :)

DTS has always had Dialnorm and DRC in the DTS specification. They decided not to use it for DVD production. As far as "dts-HD decoders are set to attenuate dialog loudness to -31dBFS", that shows you do not understand what you are talking about.Really? You have such a pleasant way of putting things.

Simply put, dialog can be recorded at any random dB FS level. That is up to the sound mixer. The encoder and decoder work together in that a -31 dB FS level that was encoded at -31 dB FS will be decoded at a -31 dB FS level. Dialnorm changes none of that.

What Dialnorm does is decrease the volume level of the entire output by the difference between the standard -31 Dialnorm value and the chosen Dialnorm value. Nothing is attenuated if a dialnorm value of -31 is used. That's correct. In fact, that's what I said - dts-HD decoders work the same as Dolby decoders - they attenuate the output so that a DN value > -31 is output at -31.

Perhaps DTS does now use Dialnorm, but does any specific DTS-HD content use a Dialnorm value other than -31 (AKA no volume reduction)?A few. Watchmen, for example.

Is there some reason you want to meader off into irrelevancies here? If you have any actual answers to the two rather simple questions I asked, please provide them. Otherwise, thanks for your contributions and please move on.

Most people use the same sound equipment for TV and disc playback. When properly implemented, dialnorm allows us to watch all such sources without needing to ride audio levels. But, since you apparently only have one DVD that you ever watch, I guess this doesn't apply to you. :)




Who rides audio levels? There is not one specific volume setting that works well for each and every DVD. That's why you have a master volume control.







Really? You have such a pleasant way of putting things.





I have been known to say worse!







That's correct. In fact. that's what I said - dts-HD decoders work the same as Dolby decoders - they attenuate the output so that a DN value > -31 is output at -31.




There you go again. You don't understnd what you are talking about. The word attenuation does not apply to a DN value of -31.

"Reference Level" is -31 dB FS!





A few. Watchmen, for example.




Watchman uses a specific dialnorm value of what in each format?






Is there some reason you want to meader off into irrelevancies here? If you have any actual answers to the two rather simple questions I asked, please provide them. Otherwise, thanks for your contributions and please move on.



Clearly repeat your two simple questions. One sentence for each question!

There you go again. You don't understnd what you are talking about. The word attenuation does not apply to a DN value of -31.

"Reference Level" is -31 dB FS!Let me translate for you. > is a math symbol that means "greater than". I wrote "a DN value greater than -31 is output at -31". That means attenuation occurs when a dialnorm value greater than -31 is entered in the metadata during encoding. No attenuation occurs when a value of -31 is entered because -31 is not greater than -31. -31 is equal to -31. Got it?

As for the rest of your post, it speaks for itself.

Great, it appears that you can not reduce your two simple questions into two simple sentences.


You seem to wonder why people do not set Dialnorm values to "the correct value" and wonder why they tend to use "the Dolby Digital encoder default value".

You have not established the fact that any particular Dialnorm value is invalid for any specific content, so the bottom line you are assuming that people do not measure dialog levels and just use the default DD DN setting of -27?

That must mean that you assume that people are incompetent, they are are fat, lazy, and stupid, or maybe they are just a bunch of pot heads?

Hey, why does the sun come up in the East and set in the West? What is the logic behind that decision? Can you provide any authoritative reason why this happens?

Boy, this gets tiresome. Thanks for dropping the silliness about my lack of knowledge about dialnorm. An apology would seem appropriate here, though.

Here's the initial post in this thread, the one you did not bother to ever read, it would appear. I have bolded the two questions:

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.
I don't wonder why people don't set proper dialnorm values. I don't think they are fat or lazy or stupid or a bunch of potheads. (Where do you come up with that stuff?)

I am curious about why Dolby chose -31dBFS as the output level for its decoder and why it chose -27 as the default input value for its encoder. (HINT: Those are my two questions.)

I suspect "because they wanted to" would be an insufficient answer. :D

There is no one ... at least to my knowledge ... participating on this forum who was an active partcipant in that decision at Dolby Labs. Therefore, in the absence of published documentation (either in the ASA, AES, or Dolby Libraries), you're not going to get an acceptable answer here. I'd suggest a lot of grief and time would be saved by directing those two questions directly to Dolby Labs.

You could PM Roger Dressler and seek his input on this.

I suspect "because they wanted to" would be an insufficient answer. :D

There is no one ... at least to my knowledge ... participating on this forum who was an active partcipant in that decision at Dolby Labs. Therefore, in the absence of published documentation (either in the ASA, AES, or Dolby Libraries), you're not going to get an acceptable answer here. I'd suggest a lot of grief and time would be saved by directing those two questions directly to Dolby Labs.

You could PM Roger Dressler and seek his input on this.

+1

Not sure why Bislander is pursuing this question. If it's purely a theoretical concern, I think everybody on this thread has demonstrated that we don't KNOW exactly how Dolby would explain its choices.

The way the questions are presented seems to suggest some concern that the decisions are bad, or potentially bad, when, as far as I can tell, the whole system is ultimately relatively neutral.

But I don't see how we get this for the first question: "First, why was -31dBfs chosen as the “proper” level for average dialog?"

It seems perfectly plain that DOlby identified (not chose) -27 dBFS as the commonest average diatlog level in movies, so to suggest Dolby has said -31 is proper seems to fly in the face of the system Dolby identified.

In essence -31 dBFS is the quietest dialog level that Dialnorm can deal with. If your movie's average dialog level is -35 dB, Dialnorm cannot "normalize" its dialog to the levels of dialog in other movies, because you've run outside Dialnorm's range. But that just doesn't appear in any way to suggest that -31 is the "proper" level for dialog. And as many on this thread have said, the Dialnorm system is not intended or designed as a system to set the "proper" dialog level in any movie, but as a way to make the dialog levels seem the same between movies without having to change your volume control.

unless there's some other burning issue underlying the inquiry, we've probably beaten this horse plenty.

I'd suggest a lot of grief and time would be saved by directing those two questions directly to Dolby Labs.I have already done that and have yet to receive an answer.

You could PM Roger Dressler and seek his input on this.I was hoping Roger would participate in this thread. Or, that one of the other people with considerable professional experience and knowledge in this area would weigh in. I guess I'll try the PM route.

Not sure why Bislander is pursuing this question. If it's purely a theoretical concern, I think everybody on this thread has demonstrated that we don't KNOW exactly how Dolby would explain its choices.

The way the questions are presented seems to suggest some concern that the decisions are bad, or potentially bad, when, as far as I can tell, the whole system is ultimately relatively neutral.
I am pursuing it for the reasons I provided earlier. Dolby gets bashed because of the way it implemented dialnorm, primarily because of the 4dB difference between -31 and -27. I have been unable to find an explanation for that gap and I thought I'd ask if someone knows the answer.

Silence or a simple "no knowledge" are perfectly fine responses.

I granted from the outset that the -27 default is likely associated with the film industry practice of recording dialog at that level. But, that's just a logical inference, and when a professional sound editor insists there's no relationship there, I thought I'd ask other professionals.

Unfortunately, there have been many responses in this thread from people who don't seem to understand dialnorm very well or who think logical inference is plenty good enough. It may be for them. But, it's not for me, which is why I asked the questions.

But I don't see how we get this for the first question: "First, why was -31dBfs chosen as the “proper” level for average dialog?"

It seems perfectly plain that DOlby identified (not chose) -27 dBFS as the commonest average diatlog level in movies, so to suggest Dolby has said -31 is proper seems to fly in the face of the system Dolby identified.But, the decoders take that movie, with dialog recorded at -27dBFS, and output it 4dB quieter, so that the dialog is now -31dBFS. Every program where the dialnorm value in the metadata is greater than -31 gets attenuated to -31 on playback. The entire system is built on the notion that average dialog should be output at -31dBFS, not -27 or any other number. Doesn't that sound like Dolby has said the "proper" level for dialog is -31dBFS?

In essence -31 dBFS is the quietest dialog level that Dialnorm can deal with. If your movie's average dialog level is -35 dB, Dialnorm cannot "normalize" its dialog to the levels of dialog in other movies, because you've run outside Dialnorm's range.OK. But, why is "-31dBFS the quietest dialog level that Dialnorm can deal with"? Why -31? Why not -35 or -27? Where did the -31 number come from? That's all I am asking.

It's possible that Dolby determined the usual range of current program content and found that -31 was a reasonable bottom end. Or, maybe there's an industry standard/practice I'm not aware of that sets -31 as minimum acceptable level for average dialog.

But that just doesn't appear in any way to suggest that -31 is the "proper" level for dialog. And as many on this thread have said, the Dialnorm system is not intended or designed as a system to set the "proper" dialog level in any movie, but as a way to make the dialog levels seem the same between movies without having to change your volume control.Yes, but the end result is that the loudness of any program where average dialog is mastered at a level higher than -31 is attenuated on playback to -31. Perhaps I should not have used the word "proper". But, the practical effect is that a TrueHD encode will often play back quieter than a PCM or dts-MA version taken from the same master.

unless there's some other burning issue underlying the inquiry, we've probably beaten this horse plenty.I'll try to PM Roger Dressler, as suggested.

Bis you are going to say you are not saying this, but you are. Here is what you said:

But, the decoders take that movie, with dialog recorded at -27dBFS, and output it 4dB quieter, so that the dialog is now -31dBFS.

This is not what happens. The dialog in a movie that is a -27dBFS remains at -27dBFS, with or without Dialnorm. Period. Dialnorm does not change the level of the dialog in the movie. It does not change anything about the mix. It just turns the whole thing down, or not. Exactly, precisely, the same thing you can do with your volume control and nothing more or different.

Dialnorm does not change the level of the dialog in the movie.

Yes, if you have 2 soundtracks on the same disk and one uses a dialnorm setting other than -31 and the other doesn't they will sound at different levels if you switch between them. The "fix" is simply to turn one up or the other down. Then the playing field is leveled. Once you adjost YOUR volume control for the dialnorm offset, the two tracks should be identical, if they are the same mix. If they are not the same mix, then all bets are off.

It just feels like something is bothering you that you are not stating. There are lots of people who complain about lots of things, from airline food to modern architecture. It seems to me that the reason you are pursuing this issue so strongly is because it concerns you in some way that may remain unstated, not just because other people raise concerns about it.

Like I said before, if it's just out of interest, that's entirely cool with me. I get stuff stuck in my craw and pursue it as hard as I can, too. But honestly, if that's what you're about, you've demonstrated the ignorance of the participants here as much as you are likely to. If actual experts are reading this and not answering, I would frankly assume that they have a business reason not to explain their research, analysis or other work product in any more detail than you can find out on the net. I mean, I could go somewhere and holler about wanting Coke's formula, or the Colonel's 11 secret herbs and spices, but they are not going to tell me, no matter how I phrase the question.

To the extent the answer to your question contains or points to information that the creators consider valuable they rationally may choose not to share that information.

Now, who's beating that horse?
Bis you are going to say you are not saying this, but you are. Here is what you said:

But, the decoders take that movie, with dialog recorded at -27dBFS, and output it 4dB quieter, so that the dialog is now -31dBFS.Guess what? That's what happens! The overall volume is attenuated by 4dB, which brings everything down, including the dialog. How far does it come down? Exactly the amount needed so that average dialog is output at -31dBFS.

This is not what happens. The dialog in a movie that is a -27dBFS remains at -27dBFS, with or without Dialnorm. Period. Dialnorm does not change the level of the dialog in the movie. It does not change anything about the mix. It just turns the whole thing down, or not. Exactly, precisely, the same thing you can do with your volume control and nothing more or different.

Dialnorm does not change the level of the dialog in the movie. Correct. The changes occur on the output side so that the dialog of all programs will play at -31dBFS. Dynamic range is not affected. Where do you get the idea that I think the mix is changed? It's not. I never said it was. In fact, I said it wasn't in response to previous post of yours. But, if you somehow got the wrong impression, allow me to correct it. Dialnorm only attenuates overall volume and does not affect the mix, dynamic range, individual channels, or anything else about the soundtrack.

Yes, if you have 2 soundtracks on the same disk and one uses a dialnorm setting other than -31 and the other doesn't they will sound at different levels if you switch between them. The "fix" is simply to turn one up or the other down. Then the playing field is leveled. Once you adjost YOUR volume control for the dialnorm offset, the two tracks should be identical, if they are the same mix. If they are not the same mix, then all bets are off.Of course. I have no problem with dialnorm and I am on good terms with the volume knob on my receiver. I am not complaining about this. I am merely asking why Dolby set it up the way it did.

It just feels like something is bothering you that you are not stating.Nope. I am simply curious about something and asked a question because I couldn't find the answer. Then, we have people like you who want to do everything except answer the question. What's that about?

There are lots of people who complain about lots of things, from airline food to modern architecture. It seems to me that the reason you are pursuing this issue so strongly is because it concerns you in some way that may remain unstated, not just because other people raise concerns about it.

Like I said before, if it's just out of interest, that's entirely cool with me. I get stuff stuck in my craw and pursue it as hard as I can, too. But honestly, if that's what you're about, you've demonstrated the ignorance of the participants here as much as you are likely to. If actual experts are reading this and not answering, I would frankly assume that they have a business reason not to explain their research, analysis or other work product in any more detail than you can find out on the net. I mean, I could go somewhere and holler about wanting Coke's formula, or the Colonel's 11 secret herbs and spices, but they are not going to tell me, no matter how I phrase the question.Well, I really don't know what to say about something like that.

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? In surveying many film mixes, it was found that the dialogue levels measured were 27 dB below full scale (0dBFS). In order to allow for some possible variation, the Dialnorm mechanism needs to accommodate more than a 27 dB range. The parameter is carried in binary data, so it was necessary to choose the smallest bitfield that would meet the requirements. For example, 4-bits = 16 values; 5-bits = 32 values; 6-bits = 64 values. It was decided to use 5-bits for the parameter, which allowed sufficient range, 0 to –31, so –31 was set as the target and “unity gain” Dialnorm value.

Second, why do Dolby encoders have -27dBfs as the default dialnorm value? 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. Exactly!

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. In order to maintain the “DTS is louder than Dolby” paradigm, they implemented it differently. Not sure how they technically justify it, or how they handle signals that have more extreme (lower) dialog levels.

Originally Posted by Sir Terrence
Personally I believe that -27 default is just a random position as to keep the audio consistent over all Dolby encoded signals.

Based on the above, we can see that this belief is incorrect.

There you go! Thanks Roger (again).

Thanks, Roger. I'd have never guessed where the -31 came from.

Thanks, Roger. I'd have never guessed where the -31 came from.

Me either, although you'd think with all the reasonably bright (I like to think) folks around here somebody would have suggested this explanation . . . . Makes perfect and simple sense once you know.

Me either, although you'd think with all the reasonably bright (I like to think) folks around here somebody would have suggested this explanation . . . . Makes perfect and simple sense once you know.
Someone did, actually.
Per the ATSC documents, Dialnorm is an unsigned 5-bit number. 5 bits = 32 possible values. These values are 1 to 31, the value zero is reserved (and is not allowed to be used in encoders.)

I missed it!! Thanks.

Someone did, actually.
Ah, sweet vindication! ;)

And thanks, Roger, for providing something "more substantial" than my musings...

Ah, sweet vindication!
Ha! Cherish the moment. Around here it's very fleeting. :D
What's shorter than a picosecond? Vindication. .... lol

But why did they pick -1db as an average level within the range? Oh yeah, modern CDs. Maybe they should have included 0db.

But why did they pick -1db as an average level within the range? Oh yeah, modern CDs. Maybe they should have included 0db.
Very funny (if it wasn't so true...) Actually, the range is 1-31, with zero being "reserved." Dialnorm is an unsigned 5-bit integer, with 32 possible values.

Yeah I realize that. Those 32 values could have been assigned to any range. 0db to -30db could have been another possibility. Conversely -5db to -35db could have also been used. I suppose one could arbitrarily use whatever scale they wish to keep audio loudness matched with the consequence on being overall softer. OK there are those FCC rules for broadcasting, but when it comes to enforcing regulations aren't they mainly responding to complaint letters from the PTC?

Yeah I realize that. Those 32 values could have been assigned to any range. 0db to -30db could have been another possibility. Conversely -5db to -35db could have also been used. I suppose one could arbitrarily use whatever scale they wish to keep audio loudness matched with the consequence on being overall softer. OK there are those FCC rules for broadcasting, but when it comes to enforcing regulations aren't they mainly responding to complaint letters from the PTC?
PTC? Let's hope not.

Yes, there are rules on the books for TV loudness, but there is no one at the FCC bothering to enforce them. Congress seems to think they can do a better job, so they've floated a few ideas that they are sure will become law. I'm not trying to be political here, but congress doesn't understand the first thing about TV and audio. Of course, I've never met a lawyer or congresscritter that didn't think they could change the course of mighty rivers, bend steel with their bare hands, etc.