Welcome to Doom9's Forum, THE in-place to be for everyone interested in DVD conversion.

Before you start posting please read the forum rules. By posting to this forum you agree to abide by the rules.

 

Go Back   Doom9's Forum > General > Audio encoding

Reply
 
Thread Tools Search this Thread Display Modes
Old 6th August 2013, 06:36   #1  |  Link
dansrfe
Registered User
 
Join Date: Jan 2009
Posts: 1,212
Fixing/regenerating clipped audio?

I recently bought a bluray for an old movie and nearly all of the 6 channels have been run through a low-pass filter, center channel especially so. Now, I realize that clipped audio cannot be restored however is there a way to algorithmically generate the clipped high frequencies to a certain degree to mitigate the effects of the audio sounding "covered up"?

Thanks in advance.

Last edited by dansrfe; 6th August 2013 at 06:38.
dansrfe is offline   Reply With Quote
Old 6th August 2013, 09:30   #2  |  Link
Ghitulescu
Registered User
 
Ghitulescu's Avatar
 
Join Date: Mar 2009
Location: Germany
Posts: 5,635
I assume the reason to do this was that the lower part of the spectrum contained hum, a common issue back then. Also the old movies did not have HD Audio , so adding something that wasn't there in the first place requires a bit of imagination.
Sometimes, the DVD issues of the same movie might help.
__________________
Born in the USB (not USA)
Ghitulescu is offline   Reply With Quote
Old 6th August 2013, 10:08   #3  |  Link
pandy
Registered User
 
Join Date: Mar 2006
Posts: 1,044
Quote:
Originally Posted by dansrfe View Post
I recently bought a bluray for an old movie and nearly all of the 6 channels have been run through a low-pass filter, center channel especially so. Now, I realize that clipped audio cannot be restored however is there a way to algorithmically generate the clipped high frequencies to a certain degree to mitigate the effects of the audio sounding "covered up"?

Thanks in advance.
I don't understand - clipped means level is cut (amplitude was to high), low pass filter (lack of high frequencies) is something else than clipped.

For really clipped audio not many things can be done, Audacity offer some limited processing with audio restoration tools.
For low pass audio technique so called Spectral Band Replication can be used to add artificially generated high frequencies that will improve perceived audio.
FFDshow is equipped with such filter (named "Crystality") - if your audio editor support direct show audio filters then ffdshow can be used however it can be unstable and will work more or less correctly only with one sampling frequency (44100) so sample rate conversion is recommended.
pandy is offline   Reply With Quote
Old 6th August 2013, 22:45   #4  |  Link
dansrfe
Registered User
 
Join Date: Jan 2009
Posts: 1,212
It's not a really old movie actually (2005). The thing is that the bluray is a remastered version of a film that was done by REM. It has two audio tracks, German and Hindi in dts-hd ma. Now, the German audio is perfect as well as the songs (which they kept intact in the hindi) however, the hindi track of the film sounds like it did with the original DVD release. Deep hum sound. Almost like I'm hearing it from another room. I'm not sure if that's clipping or something else.

Although it's not a topic of this thread, I'm quite interested to know how REM managed to work with the original hindi track and fix it to near pristine audio fidelity for use in the German track. Did they have a different source to work from altogether? My main goal here is to replace the German track's center channel with the Hindi track's center channel yet use all of the channels in the song portions of the German track.

Two issues with this:

1. If I cannot manage to get the Hindi center track to match the audible frequencies of the German track's side and back channels then the final mix will sound odd and the whole process will be moot.

2. I'll have to find the parts of the audio in which the dialog delivered has an echo effect which permeates through the side and back channels. In those parts I'll have to use the affected channels (probably all) from the hindi track and apply the same fix to those channels as done to the center channel.

It might be time to start learning German.

Last edited by dansrfe; 6th August 2013 at 23:13.
dansrfe is offline   Reply With Quote
Old 8th August 2013, 08:55   #5  |  Link
dansrfe
Registered User
 
Join Date: Jan 2009
Posts: 1,212
Quote:
Originally Posted by pandy View Post
I don't understand - clipped means level is cut (amplitude was to high), low pass filter (lack of high frequencies) is something else than clipped.

For really clipped audio not many things can be done, Audacity offer some limited processing with audio restoration tools.
For low pass audio technique so called Spectral Band Replication can be used to add artificially generated high frequencies that will improve perceived audio.
FFDshow is equipped with such filter (named "Crystality") - if your audio editor support direct show audio filters then ffdshow can be used however it can be unstable and will work more or less correctly only with one sampling frequency (44100) so sample rate conversion is recommended.
Yeah, I'm not really sure of the specific term to accurately describe the issue.

I was looking at trying Izotope RX 2. Would Spectral Repair, Declipper, or the Hum Remover be of use in this situation? Should I look into trying some other software? Will Audacity give provide optimal results in your opinion? To be honest, I'm not too sure where to begin with the software.

Also, would uploading a small cut of the dialog and/or song portion from both german and hindi tracks help identify the problem? With or without the echo parts?

Thanks.
dansrfe is offline   Reply With Quote
Old 8th August 2013, 10:40   #6  |  Link
Ghitulescu
Registered User
 
Ghitulescu's Avatar
 
Join Date: Mar 2009
Location: Germany
Posts: 5,635
German tracks are always reworked, so they sound better even than the originals (it includes Hollywood here, not only Bollywood).
__________________
Born in the USB (not USA)
Ghitulescu is offline   Reply With Quote
Old 8th August 2013, 12:01   #7  |  Link
dansrfe
Registered User
 
Join Date: Jan 2009
Posts: 1,212
By reworked do you mean that they start from a different source provided by the film studio altogether or they have specialized audio engineers that actually fix the audio from the original source?
dansrfe is offline   Reply With Quote
Old 8th August 2013, 14:45   #8  |  Link
Brazil2
Registered User
 
Join Date: Jul 2008
Posts: 479
Quote:
Originally Posted by pandy View Post
FFDshow is equipped with such filter (named "Crystality") - if your audio editor support direct show audio filters then ffdshow can be used however it can be unstable and will work more or less correctly only with one sampling frequency (44100) so sample rate conversion is recommended.
Still, ffdshow is a great piece of software, a jewel, and it's a pity no ones wants to take over its development
Brazil2 is offline   Reply With Quote
Old 8th August 2013, 23:38   #9  |  Link
dansrfe
Registered User
 
Join Date: Jan 2009
Posts: 1,212
Here's a 1min cut of the same time frame from the center channels of both language tracks: https://www.dropbox.com/s/lglh21tsa1...comparison.zip. Honestly, I'm not sure where to begin. The german audio sounds like it was recorded and mastered entirely differently.
dansrfe is offline   Reply With Quote
Old 9th August 2013, 03:22   #10  |  Link
raffriff42
Retried Guesser
 
raffriff42's Avatar
 
Join Date: Jun 2012
Posts: 1,376
It's got what sounds to me like moderate intermodulation distortion, spread across all frequencies. Probably a bad optical sound track. Can't filter that stuff out. Exiters only make it sound worse. Best result for me was with a 5kHz low pass, followed by a treble boost hinging at 1.5kHz.
raffriff42 is offline   Reply With Quote
Old 16th August 2013, 18:00   #11  |  Link
dansrfe
Registered User
 
Join Date: Jan 2009
Posts: 1,212
Hey raffriff42, which program did you use to run the audio through a low pass/treble boost? Audition or something else? Thanks!
dansrfe is offline   Reply With Quote
Old 16th August 2013, 18:45   #12  |  Link
raffriff42
Retried Guesser
 
raffriff42's Avatar
 
Join Date: Jun 2012
Posts: 1,376
Audacity IIRC, I did something like:
Low Pass, 5000 Hz, 24 dB/8ve, followed by
Equalizer, with all sliders flat up to 1 kHz, gradually increasing to about +8 dB at 5000 Hz (in hindsight, should have simply used Bass and Treble)
raffriff42 is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +1. The time now is 13:23.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2020, vBulletin Solutions Inc.