Repair ac3 because of dialog norm changing ?

[Music Fan]

Hi,
I recorded a show on HDTV with 5.1 sound (ac3 @ 384 k) and the level of Dialog Normalization brutally changes (in the middle of the show) from -6 to -16 db for a few seconds and comes again to -6 db.
I see this figure on my receiver, and I hear it of course.
I often have this problem on this TV channel and never on others, so I guess they have problems with their ac3 encoder.
I copied the sound on my pc by the Spdif output, I put the ac3 file in an avi container, and when I play it on my dvd player, this problem is still there (it makes sense).
I'd like to repair it if possible.
Is it a kind of "header" problem in the ac3 file that could be solved without re-encoding ?
If no, I guess I should cut this part, decode to PCM, increase its level to the same than the rest of the file, encode it again in ac3 and join the parts. Not very simple.
Any other ideas ?

[Ghitulescu]

Any commercials?
Have you checked the raw/original file for transmission errors?

[Kurtnoise]

use eac3to to decode your entire file to wav and transcode it with aften using -dnorm switch...

[Music Fan]

I'd like to avoid to re-encode all the file. Anyway, even if I do that, what will happen with the -16db part ? I'd like to understand this problem.

Any commercials?

No of course, I wouldn't have asked this question in this case. This problem lasts 3 seconds in the middle of the show and happens sometimes several times by minute.

Have you checked the raw/original file for transmission errors?

Of course (again), I explained it above. I have it on my set top box and also with the sound played from my pc.

[Shirtfull]

Originally Posted by Music Fan

Of course (again), I explained it above. I have it on my set top box and also with the sound played from my pc.

you have only checked the output from your settop box and not the raw file for TX errors

[Music Fan]

My set top box is crypted, I can't transfer its content to an external drive, so, the Spdif output is the only way to copy the 5.1 sound.
I don't know what is TX error but how do you explain that this error is still in the ac3 file played from my dvd player ?

[TinTime]

eac3to will remove dialnorm without transcoding:

eac3to.exe input.ac3 output.ac3

[Music Fan]

Thanks, it worked , but not directly.
I first had this message :

The format of the source file could not be detected.

Thus, as advised in the FAQ, I tried Delay Cut ;
http://en.wikibooks.org/wiki/Eac3to/...be_detected.22

In Delay Cut, I ticked "Fix" under CRC errors.

Then the file was accepted by eac3to and the dialog norm problem is not there anymore !
Weird detail : eac3to detected a -25db level for dialog norm and not - 6 as I expected.

I also tried the file created by Delay Cut before using again eac3to, but the dialog norm problem was still there, so I need both programs.

Question : is the dialog normalization really useful ?


edit : I read the debut of this article ;
http://en.wikipedia.org/wiki/Dialnorm
and I believe I understand why the level was 25 (and not - 25) : the maximum value of dialog normalization is 31 (= 0 db), so 25 equals -6 for the receiver.

[TinTime]

Originally Posted by Music Fan

Question : is the dialog normalization really useful ?

I think it would be useful if it was used universally. But it isn't

Originally Posted by Music Fan

edit : I read the debut of this article ;
http://en.wikipedia.org/wiki/Dialnorm
and I believe I understand why the level was 25 (and not - 25) : the maximum value of dialog normalization is 31 (= 0 db), so 25 equals -6 for the receiver.

Yes, that's right.

[Music Fan]

Originally Posted by Music Fan

I also tried the file created by Delay Cut before using again eac3to, but the dialog norm problem was still there, so I need both programs.

Not always actually.
This test was made with a short part of the ac3 file cut and extracted with Virtual Dub (I had previously put the ac3 file with a video in an avi container with Virtual Dub Mod).
But I tried eac3to with the entire ac3 file, and it was accepted without having to fix problems with Delay Cut.
And the dialog norm problem has well been removed.

I guess it means that Virtual Dub can't cut and/or extract correctly ac3 from avi, unless the problem comes from the mux done before with Virtual Dub Mod.