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AC3 settings

seciors

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I'm trying to create the 5.1 AC3 file for my SW Episode 1 edit and I'm finding it a bit overwhelming.

I have Apple's Compressor application which gives me access to most of the settings one would use when creating an AC3 file. I went with the defaults, which are:


AUDIO
Enable Low Frequency Effects (checked)
Dialog Normalization: -24dbFS
BITSTREAM
Center Downmix: -3dB
Surround Downmix: -3dB
PREPROCESSING
Compression Preset: Film Standard
General: Digital Deemphasis (NOT checked)
LFE Channel: Low Pass Filter (checked)
Full Bandwidth Chan. Low Pass Filter (checked)
Full Bandwidth Chan. DC Filter (checked)
Surround Channels: 90 degree phase shift (checked)
Surround Channels: 3dB Attenuation (NOT checked)

But I'm not sure if these are the best settings to use. When I listen to the resulting file on my surround system (which isn't the best, but I'm not listening for each channel...see below), I need to turn the general volume up as compared to non surround sound source material. Like...way up.

My speaker uses negative db numbers to indicate volume. I don't really get it, but that's the way it works. Normally, material we watch usually is loud enough in the -40db to -45db range (sometimes up to -50db).

With the above settings, I need to go down to -25db to really feel like the sound is at a good level.

(as another point of reference, if I let Handbrake create the AC3 file [it gives me no DRC options at all], I set the volume to around -30db - -35db.

So I guess I'm trying to find out if I need to change any of the above settings, or how I can possibly figure out what the settings should be? I know it depends a lot on the source material, but lots of people have made edits using Episode 1, so I'm hoping there might be some people out there who have already gone through this process and can give me some guidance on this.

Thanks for any help anyone can provide.
 

seciors

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So here's an old thread where I asked this same question 2+ years ago for my original ROTS release (ahh, the irony!).

http://www.fanedit.org/forums/showthread.php?4989-5.1-surround-sound-dialog-normalization

geminigod provided tons of valuable info. I'm wondering though, since in the last post on the thread says he decided to forgo using dialog normalization (and any DRC pre-processing), if that is still his opinion on the matter.

I also find it interesting that Apple's Compressor changed its default setting from -27 to -24.

Either way, I'm beginning to suspect that I should redo my AC3 file with either a higher dialog normalization (e.g., -27), or just take the route of no DRC at all.

Any opinions on the matter, gem, or anyone else?

Thanks!

PS - can someone tell me what the difference is between DTS and AC3? DTS apparently does't use DRC...is it possible to create a DTS file as a fan editor? Or are we pretty much stuck with AC3?
 

seciors

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Quick update:

First, I was wrong about Compressor changing the default setting - I used the generic AC3 preset instead of the one meant for disc authoring (which still has -27db as the default. doh!)

Second, I know I should have thought of this earlier, but I made a comparison with the TPM BD. On my system it plays using DTS.

I used the opening "failed negotiations" scene for comparison, as it has normal dialog (Obi-Wan and Qui-Gon waiting to be met) as well as a loud explosion (ship being destroyed) and a battle scene with light sabers, a force push, and varying music levels.

I set the sound level on my speaker to -31dB, which seemed to be an acceptable level, where I could appreciate the full range of sounds. The sound from the BD was very good at this level, and all the different types of sounds came through clearly and effectively. Personally I would normally set the volume a bit higher, but that's probably because my hearing isn't like it used to be (and I like to have movies be slightly louder anyway). But the -31db level worked very well for the BD.

Then I put my AVCHD in, changing absolutely nothing about the setup.

The dialog sounded slightly quieter, but wouldn't be a huge problem. However, the full dynamic range (explosion, battle, force push) felt compressed and not as full ranged as the BD. The subwoofer was definitely less noticeable. I'd have to raise the speaker volume to achieve a comparable experience to the BD most probably.

Based on this, I'm thinking I need to try some tests with new settings (I'd just use this single sequence, as it seems to be a good representation of dynamic range). I'm thinking of trying the following settings (anything not mentioned remains the same as previously described):

1. Dialog Norm = -27dbFS (which IS the real true default setting after all!)
2. Dialog Norm = -27dbFS; Compression preset = NONE
3. Dialog Norm = -27dbFS; LFE low pass filter OFF

4. Dialog Norm = -31dbFS;
5. Dialog Norm = -31dbFS; Compression preset = NONE
6. Dialog Norm = -31dbFS; LFE low pass filter OFF
 

seciors

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LOL. Man, my brain is frazzled! (fixed.)
 

Captain Khajiit

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seciors said:
PS - can someone tell me what the difference is between DTS and AC3? DTS apparently does't use DRC...

The difference is that they are different codecs. They both compress audio. As you point out, the main difference is that DTS does not use DRC. For AC-3, setting DRC to none and dialnorm to -31 is the equivalent of not having DRC at all, which explains why you felt that you appreciated the full range of sounds with these settings.

Many people believe that dialnorm is obsolete because players and amps tend to have their own dynamic compression settings these days e.g. my media player has a night mode that does its job well. This is why Eac3to has no option to set DRC when encoding AC-3. Despite all this, I tend to use DRC and set dialnorm when using AC-3.

is it possible to create a DTS file as a fan editor?

Yes. Have a look at this thread. I have never shared the enthusiasm for DTS though. DTS tracks tend to be recorded at a higher volume level, and this (combined with the absence of DRC) is the reason that so many people claim to prefer DTS audio. In my opinion, DTS is a waste of space, at least on a DVD.
 

seciors

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Thanks for that info about DTS. The thread (by geminigod) hasn't been updated in a while, and warns that Mac users are not supported anyway. I'm fine with AC3, as long as I can get it to work right. ;-)

My speaker, AND blu ray player both have settings that seem to affect DRC. I don't know if having DRC inside the file as well as using settings in the player is a bad thing. Hopefully they complement each other.

Can I ask why you still set dialnorm even though it seems obsolete? What do you usually set it at?
PS - do you also usually set a compression preset, and is it Film Standard?
 

Captain Khajiit

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seciors said:
Can I ask why you still set dialnorm even though it seems obsolete?

I tend to set dialnorm because I do not feel that it conflicts with the DRC settings of other devices (which can always be switched off if necessary). Moreover, the dynamic range on BD audio tracks these days is usually far too high for my taste and rarely suits the average home environment, so every little helps.

EDIT: Furthermore, for fanedit releases, it does not hurt to err on the side of caution with such things, as people often comment on high dynamic range (usually without realizing that it is present in the source).

What do you usually set it at? PS - do you also usually set a compression preset, and is it Film Standard?

If my source audio was AC-3 and had a dialnorm value, I use that value upon recompression (with Film Standard) unless I have made extensive alteration to the audio in terms of levels. Otherwise, I simply use a dialnorm of -27 with Film Standard, which almost always works well enough, in my experience.
 

seciors

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Thanks for all the information and help Captain!
 

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Ok, so I did my testing, and here are the results.

First, moving to -27db for dialnorm definitely improved things. It still wasn't quite up to the same level as the TPM DTS sound, but that kind of makes sense given that DTS has no DRC.

-31db increased the overall volume even more (as is to be expected). I think it sounded even slightly louder than the TPM DTS. Not 100% sure why, but it must have to do with either my blu ray player or speaker/amp doing something to the DTS levels that is akin to DRC. The difference wasn't huge, but I think noticeable.

While -31db certainly allowed me to lower my volume level on my speaker, I tend to think the Captain has a point about "assisting" people with dynamic range, and people can always turn up the volume if they feel it is not loud enough.

Film Standard compression seems to provide a pretty wide dynamic range,and thus using it seems like it is not detrimental.

Based on this, I think the best route is to go with -27db and Film Standard, and keep all other settings the same.

Regarding the LFE low pass filter, I'm really not sure I could tell a difference when it was on or off. That's probably because it did nothing.

Here's what the documentation says about this setting (from Apple's Compressor online manual, which is the software I'm using):
Apply Low-Pass Filter: Select this checkbox to apply a 120 Hz low-pass filter to the Low Frequency Effects (LFE) channel. Turn off this filter if the digital signal fed to the LFE’s input does not contain information above 120 Hz.

Thus, I see no need to turn this off, since it is safer to prevent any LFE info above 120Hz to go to the subwoofer anyway (I think), and I see no harm in keeping it checked. Please correct me if I'm wrong.

If anyone has any final suggestions on what I should use for dial norm or any other setting, please feel free to chime in. Otherwise, I appreciate the help I've received, and hope this thread may someday help someone else!
 

seciors

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Now I'm having second thoughts. I'm thinking about not applying any DRC. (-31db, no compression)
Just found out that this is what A9 does, and though geminigod hasn't weighed in on this thread, from what I read last, he was considering not using it either. Finally, the two reasons that also support this decision are that DTS doesn't use it, and almost all speakers/players/receivers have the ability to apply DRC and usually it is a default.

Can someone talk me out of doing this? Is it really a big deal? What danger is there in not using DRC, other than requiring the listener to lower the volume in the beginning. And correct me if I'm wrong, but none of this affects the stereo downmix.
 

Captain Khajiit

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seciors said:
Is it really a big deal?

No. Eac3to and some other audio tools do not even have the option to set DRC, so feel free not to do so.
 

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Ok, thanks once again! I am probably going to do one more test with a larger sample where I can try to get some quiet dialog and an action scene that is loud., I also want to try out -29db dialnorm since it is halfway between the two.

Thanks again so for helping me Captain!
 

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Sorry, been out of town. seciors, sounds like you are good to go. I need to go back and re-look at that old thread of mine you mentioned. I seem to recall that what I wrote is more useful for original audio work vs. the already finished tracks we are manipulating. The original intended use of these Dolby settings that I was trying to describe have long since been defeated by modern digital technology and the studio's quest to make everything as loud as possible. Most of the studio AC3 tracks that you are pulling as source audio are probably packaged as film standard with DN set at -29 or -27. You probably want to create your AC3 with similar settings.

Most importantly make sure there isn't any clipping going on in your edit's audio (there probably is after unpacking the audio in order to import and edit it). This can be manually adjusted for or re-packaged with the above settings to compensate.
 

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seciors said:
So here's an old thread where I asked this same question 2+ years ago for my original ROTS release (ahh, the irony!).

http://www.fanedit.org/forums/showthread.php?4989-5.1-surround-sound-dialog-normalization

geminigod provided tons of valuable info. I'm wondering though, since in the last post on the thread says he decided to forgo using dialog normalization (and any DRC pre-processing), if that is still his opinion on the matter.

Oh, to answer this. Yeah, so I gave up entirely on the dolby DRC settings a while back, but that doesn't mean you can't use the settings described in the previous post or ignore all of this completely for that matter. Now I manually adjust the balance, range, and levels, which is preferable IMO, but it is more complicated and time consuming for marginal improvement in overall sound quality compared to doing nothing. The same can be said of screwing around with DTS over Dolby Digital (DTS supports higher bitrates and subjectively better overall sound quality). It is a bit like fanediting in general. Either you do it because you like to fuck around with it or you don't. There is a good chance the audience won't notice the difference or might even complain if they do.

Quite honestly people are more likely to complain when there is a wide dynamic range or they have to turn their volume way up than they ever will from it being "too loud" or "too compressed" or from some miniscule audio clipping. This is exactly why sound studios have changed how they engineer sound over the past few decades. What the majority consumer wants, the majority consumer gets.

EDIT: Additional questions in this thread: 1) low pass filter doesn't matter either way for fanedits. More useful for original audio recordings. 2) It doesn't hurt to include the dolby digital DRC settings because it is just metadata. As CK mentioned, most modern programs can ignore it or apply their own settings. It is more of a convenience thing and backwards compatibility thing for viewers.
 

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Hi gem, welcome back, and thanks for taking the time to provide your valuable feedback to this thread!

one of the things I do as a final task for my edit is to examine the audio levels, and key frame places where the levels are getting high. fCPX has a nice feature that auto-colors your waveform in the timeline to warn you of audio that goes over -6db (yellow) or hits 0db (red).

so I go through my final edit and address these areas if they exist. In this edit, I probably had two places that briefly hit 0db, not enough to sound like clipping, but could end up as a problem in a stereo downmix (or just because of the large dynamic range). So I key framed those down a bit. I also had many places that were yellow. Again, I key framed those specific places so they either were just out of the yellow zone, or barely touched yellow (sometimes I allowed them to be in the yellow if I felt it was warranted based on the individual situation). I did all this first for individual sound channels, and again looking at the final downmix. So I believe the edit is safe from being too loud.

i think as a goal, it is reasonable to aim at a sound level close to the blu ray sound level, with regards to what people should expect in terms of having to turn up/down their volume. These levels on my system are very different than other sources I listen to, which are (sadly) mostly TV shows my kids watch via Netflix and iTunes, which require the volume to normally be set much higher. I think this i evidence of your comments regarding the increased loudness many modern programs use these days. We are always telling the kids to turn the volume down, LOL.

But I figure if I provide sound levels close to the original source, people shouldn't complain too much.

Finally, I think both you and CK have excellent points about modern equipment already doing their own DRC. And people listening to a downmix should be protected by the key framing I already mentioned (and the -3db attenuation done by AC3 which is regardless of the dial norm and compression settings, at least I believe that is the case!)

now I just need to get 3+ hours of time with my TV/surround system to do the testing, and not get complaints which is not easy! :p

Thanks again to both you and CK for this invaluable advice and help!
 

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Ok, I've listened, compared, and soul searched. I've decided on going with -29db and DRC. I think it is better to have people turn up their volume than have to turn it down, and the difference is really not that huge. But I feel more comfortable having the DRC available.
 
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