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marc148
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Declicker shortens audio file

May 18, 2012 8:17 AM

Tags: #cs5.5 #audition #declicker

I have several (mp3) audio files and when I use declicker repair (it usually finds about +1000 clicks) the audio file is shortened. I understand that clicks are removed instead of silenced and that leads to shortening my audio files with seconds. Is there a way to declick in a better way and keep the audio length the same as before the declicking process?

 

Marc

 
Replies
  • Currently Being Moderated
    May 18, 2012 9:44 AM   in reply to marc148

    Hi Marc,

     

    I don't think the DeClicker should be changing the duration of your files in any way.  How much of a change in duration are you seeing?  Any chance you can post a screenshot of your Diagnostics panel settings and perhaps a before and after shot of the Properties panel for a file?  If you wish, you may send it to audbugs@adobe.com instead of posting to the forums.

     

    Thanks,

    Durin

     
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  • Currently Being Moderated
    May 18, 2012 3:22 PM   in reply to marc148

    I do quite a lot of declicking and I've never seen anything like this.

     

    Can you give some more details?

     
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  • Currently Being Moderated
    May 18, 2012 4:52 PM   in reply to marc148

    I notice the duration displayed in the Fles panel remains the same.  I'm not sure why you see a discrepancy in the properties panel.  I'll need to look into that more.  Are you certain, apart from the change in displayed duration, that the actual file length is reduced? 

     
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  • SteveG(AudioMasters)
    5,615 posts
    Oct 26, 2006
    Currently Being Moderated
    May 30, 2012 10:05 AM   in reply to marc148

    marc148 wrote:

     

    So today I played some more with Audition and what I've noticed is that when I open an mp3 file and I immediately

    save it (mp3 128kb cbr) it will also reduce the file with several seconds (as reported by Windows explorer) and in Audition itself by milliseconds.


    I find it very confusing that Windows reports a different audio length. Not sure what to make of it.

    If you'd said that it increased the length of the file, I might have believed you...

     

    Opening an MP3 in Audition will decode it into an uncompressed wav file. Resaving it as another MP3 will re-encode it, and probably add silence at the start. Also, because its a re-encode, the quality will be lower. MP3 is a distribution format, not a production one, and as such isn't intended to be manipulated like that under normal circumstances. I'm assuming that the time addition is still there, although I haven't checked recently - it was done like that previously because some players notoriously cut off the start of MP3 files before playing them.

     
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  • Currently Being Moderated
    May 30, 2012 10:26 AM   in reply to SteveG(AudioMasters)

    Ack.  I meant to reply to this over the weekend but got sidetracked cooking burgers.

     

    MP3 and other compressed formats can be difficult to accurately determine the duration of without scanning the entire file.  You'll notice that when you open an MP3, the duration may change after the conforming process has completed.  We make an estimate based off the file size and bitrate, but until Audition has generated an uncompressed version, the exact length remains approximate.  Depending on the compression level and the original encoder, this can sometimes be off by a lot.

     

    Your screenshots had me confused, but I've just been able to reproduce an issue where the Properties panel duration isn't updated when the file is conformed.  That would explain the discrepancy between Files panel duration and that in the Properties panel.

     

    In essence, I don't THINK DeClicker is actually changing the length of your files.  If you hear missing bits during playback, let's keep talking.  However, I suspect it's simply the fuzzy duration estimation combined with a small update bug.  (The Properties duration field is updated properly when switching back and forth between files.)

     
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  • SteveG(AudioMasters)
    5,615 posts
    Oct 26, 2006
    Currently Being Moderated
    Jun 5, 2012 6:14 AM   in reply to marc148

    marc148 wrote:

     

    Also in the properties panel I see the acronym OFL behind the mp3 settings. What does that mean?

     

    Ah, now we might be getting somewhere! This stands... wait for it... for Original File Length. At this point, you need to read AES paper 5830 really, but the gist of it is that when you encode MP3 files, the results aren't expected to be accurately time-aligned with the original file, due to all sorts of things to do with the need for look-ahead, data block structuring, etc. What Fraunhofer have done with the present encoder is to find a way of compensating for this, and supposedly getting the original timed length of the file back.

     

    Now without investigating this a lot more, I can't tell you how successful or otherwise this actually is. The decoding process itself can also (apparently) make a difference to the outcome, and what gets reported by some software isn't necessarily the same as what gets reported by others.

     

    As I said earlier, MP3 is supposed to be a distribution format, not a production one, so in essence these timing issues would not be deemed important normally.

     
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