Low volume after authoring .m2v and .ac3, why?

[Josip1]

Everty time I compile .m2v and .ac3 files useing IfoEdit v.95 the audio is very low, roughly 40% lower that the original movie:angry:. When I compile .m2v and .dts audio track. The audio played back is the exact volume as the original.

I am stumbled:confused: to why this would be happening. I used DVD Decrypter to demux the main movie .m2v and the main audio track .ac3. Once that is done I use IfoEdit to author the dvd.

The only thing i can think of that is causing the problem is either DVD Decrypter is not demuxing the audio track properly or it has something to do with IfoEdit not entering the correct gain levels in the main ifo file.

Any advice or thoughts from a guru would be great? :)

Thanks

[TRILIGHT]

This is an IFOedit question so I am moving it to that forum. You may get a faster answer.

[REECYCUP]

this may not help but
if i take out the ac3 2 channel
and leave only the ac3 5.1________the volume is much lower(not 40%)
if this isnt what your doing i cant help because ifoedit nor dvddecrypter change the audio bitrate or volume
i could be wrong:)

[Josip1]

What do you mean by only taking out the 2 channel and leaving the 5.1 channel? I was a bit over the top when i said it was a 40% in volume drop. Its probably more like a 15% drop in volume.

The procedure i follow is by taking out the main .m2v and .ac3 (5.1 channel) with dvd decrypter and take out the chapters. Then I compile them using the author dvd function in Ifo Edit and it muxes the 2 files to create vob and ifo files.

Am i doing something wrong?:confused:

If there are other procedures of compiling a dvd movie with the just the main video and audio stream please pass them along. :D

[VidHack]

OK,
I am reading the original Post and asking myself some basic questions? Actually alot of questions.
quote:
"Everty time I compile .m2v and .ac3 files useing IfoEdit v.95 the audio is very low, roughly 40% lower that the original movie. When I compile .m2v and .dts audio track. The audio played back is the exact volume as the original."
You say the volume is low - are you controlling this test? Are you comparing the volume from a software player against a stand alone dvd player? Are the exact same audio filters/codecs being used to play back the original and then the copy? Did you examine the AC3 header for alterations? Did you rip the AC3 file back off the muxed copy and run a CRC check against it, to look for alterations of bits? Actually this question might be moved to the Audio_Encoding Forum, as its a AC3 question, which, if using BeSweet for AC3, there is known volume problem. There are many tests to find out whats happening, but we would need to do do alot of testing..to nail it.

VidHack

[Josip1]

Hopefully this will explain my process a lot clearer.
I demux the main .ac3 and .m2v from the vob files using dvd decrypter.
I mux them using the dvd author option in IfoEdit. once it has finished its job, i burn the vob's/ifo's using nero. I have compared my copied version to the original movie and the copied version is lower in volume. On my stand alone dvd player(Toshiba Sd-2500) I play the movie on my system at volume 27 and its very loud. To get the copied version to equal loudnes i have to put it to like 33.

Ive noticed that when i use .dts audio track the volume level for copied movie is the same as the original. If I can pin point the problem, then you could move this post/thread into another area of the Forum. Till then I am not sure if dvd decrypter/vobedit is extracting the audio track properly. My first guess would be that ifoedit isnt insurting the proper settings into the ifo file, such as audio gain....

[VidHack]

Originally Posted by DSPguru (in another forum)

this is 'how to'-(Change AC3 volume)
change dialnorm in the bsi (to -6db) on the headers of all ac3 frames in the extracted stream.

one of the BeSplit's versions (0.9b1 maybe?) had offered this feature..
this isn't offered anymore.

This post has been edited by DSPguru on Apr 18 2003 - 01:58 AM


VidHack

[VidHack]

Copied From:

http://www-mice.cs.ucl.ac.uk/multimedia/misc/avt/IETF47/internet-drafts/draft-gharai-ac3-00.txt

2. AC-3 Digital Audio

An AC-3 audio stream is constructed as a sequence of synchronization
frames also called the sync frame. Each frame is completely self
contained and is made up of:

o a synchronization information (SI) header, which includes:
- a sync word, used for acquiring and maintaining synchronization
- an indication of the sampling rate, 48kHz, 44.1kHz or 32kHz
- and the size of the sync frame
o a bit stream information (BSI) header which includes the sync
frames' timestamp,
o 6 audio blocks (AB), each block represents 256 new audio samples,
o an auxiliary data field (Aux),
o and finally, an error check field CRC.

-------------------------------------------------------------
| SI | BSI | AB0 | AB1 | AB2 | AB3 | AB4 | AB5 | Aux | CRC |
-------------------------------------------------------------
Figure 1. An AC-3 synchronization frame (not to scale).

All sync frames within a sequence are the same size. Frame sizes range
from 128bytes to 3840bytes. Table 5.13 in [1] lists all possible frame
sizes per bit rate and sampling frequency. At 48kHz each sync frame
represents 32ms of audio data (each audio block is 5.33ms).

Each sync frame is a complete independent data unit, it does not require
any other data to be decoded. A complete sync frame MUST be presented
to the decoder for decompression. An incomplete sync frame will not pass
the decoder's error detection test causing the decoder to mute. At 48kHz
this can cause a maximum of 64ms of muted audio (if decoder is unable to
synchronize with the immediate next sync word).


-----------------------------

OK,

You might have found a bug with the IFOedit AC3 muxing routine, so if you know how to use a HexEditor then examine the BSI packet and tell us what you get by comparing the original to the new muxed copy. This could be interesting, as I dont know of this bug being reported before. Good Luck

VidHack

[Josip1]

I d/l WinHex 10.75 and did a compare on the original .ac3 and the newly muxed copy that i extracted out of the vobs using vobedit.
They all were identical. I tested it on 3 of my movies to make sure, and all 3 of them were identical.

Another thing that i forgot to mention was that not all my movies with .ac3 audio stream are lower in volume compared to the original. They vary. Back to the Future 1,2 and 3 were all realy lowest in volume that i came across. I have also came acros some movies that are werent lower in volume.

Just curious is there any cofiguration settings inside the ifo files that overide gain levels? Thats the only thing i can think of that would be happening.

I was wondering if anyone else has had problems like i have?
Maybe people have been but havent posted anything or just havent noticed the change in volume level.

I am very confused:confused: and frustrated:angry: why this is happening. I know i am doing the procedure the right way cause they are very simple!

[mpucoder]

Take a look at the audio attributes of the original ifo and the one created by IfoEdit. That is the only area of an ifo that can affect audio, afaik. You can either post just the differences, or email both ifo files zipped, to me (mpucoder@attbi.com) and I'll look at them. But please don't post the files themselves.