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Bad Audio after transcoding

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PRgraphist
Bad Audio after transcoding
on Sep 30, 2006 at 3:02:00 am

I have a couple os videos that I edit on premiere and export to .AVI file. All looks fine, the avi files, the premiere and encore timelines, but when i transcode to an DVD-R the audio are bad, sounds like the audio channels are duplicated ant put out of Sync. Imagine the premiere timeline with two audio tracks with the same songs and one of the tracks are a little "rewinded" in relation to the other. I think this is a transcode issue, but anybody had a idea or tips about the best transcode settings..

I use premiere 1.5 and ecore 1.5 with the update allready installed


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Neil Wilkes
Re: Bad Audio after transcoding
on Sep 30, 2006 at 10:51:30 am

The Dolby DIgital transcoding in Encore has no user settings available, so any problems lie in the source material.
There are a couple of things that spring to mind here, depending on what the original source material was.
If it was originally MPEG audio, or MP3, then the problem is recompressing material that has already been heavily compressed & this will always result in quality loss. The lower the bitrate of the MP3.MPEG audio, the worse the quality will be.
Option 2 is if your source was 16/48 PCM WAV in Premiere, again - what was the original source?
Did you possibly use any form of processing on the Audio?

Can you please be a lot more specific about your transcode setting (Dolby Digital? MPEG?) and the source of your audio files?



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PRgraphist
Re: Bad Audio after transcoding
on Sep 30, 2006 at 5:34:00 pm

One of the videos had the original audio from the camera, so the audio is the default setting of NTSC DV. And for other editon I take a MP3 file to make a "kolash" with the original source videos. I use the default transcode settings of Ecore, so the audio is dolby digital... OK another question, the recompression issue that you say, is on Premiere or in Encore, because the .AVI files sound fine. another abservation... the sound problem is only when I play the DVD in my DVD player (APEX AD-1225, very cheap thing), but when play the same disc on my PC the audio are fine... It posible that the DVD player are damage or something, because before I made exactly the same proccess of editng and DVD authoring and this DVD player work great.


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Neil Wilkes
Re: Bad Audio after transcoding
on Oct 1, 2006 at 2:51:08 pm

Using an MP3 file in any DVD production is always going to be a risk.
MP3 has already "thrown away" 11/12 of the original audio, and what remains is all there is left to work with.
When this gets imported into Encore, it will first turn it into a 16/48 PCM file by "Filling in the gaps" with zeroes. It can never replace what the original MP3 compression threw away - that information is gone forever.
When this gets recompressed to Dolby Digital, another 10/12 gets thrown away again.
With most audio, the quality loss is appalling and very noticeable.
Occasionally, if the audio is not complex or detailed, you may get away with it, but sooner or later - usually sooner - what you describe is going to happen.

Another possible source of trouble could be the settings on your camcorder.
Unless these have been set - by you - to 16/48, the defaults will be 12 bit at 32 KHz.
Again,. this is losing top end detail as the highest possible frequency will be a mere 16KHz.
and 12 bit audio is 256 times lower in resolution compared to 16 bit.

Double check your camera settings and make certain you are filming at 16/48.
And avoid using MP3 - it is a dreadful sounding format at the best of times, and completely unsuitable for DVD.




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PRgraphist
Re: Bad Audio after transcoding
on Oct 1, 2006 at 8:12:58 pm

OK... I understand that you say, but ir apply when i use MP3 in premiere and render the movie to an avi file?. Why the problem do not appear when I play the dvd on my PC?. And here is other observation, I notice this problem when a play the DVD on a MONO TV (not Stereo), but I play on other TV (Stereo, This time) and work FINE. The problem is the TV?.


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Neil Wilkes
Re: Bad Audio after transcoding
on Oct 2, 2006 at 8:58:08 am

If the mono compatibility of the Audio is not correct - and this has not been mentioned before - then the problem can come from not only the use of MP3 > WAV > Dolby Digital recompression, but also from the original encoding of the MP3 itself.
For example, in some MP3 encoders, there are different options for stereo, or dual mono, or even some form of "enhanced" stereo.
Did you ever check the mono compatibility of your audio?
If there are phase variances between your left & right channels, then cancellation will do the rest.
My money is still on the MP3 file though.



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PRgraphist
Re: Bad Audio after transcoding
on Oct 2, 2006 at 2:21:52 pm

ermmm... How I can check the mono capabilities of the Audio?


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Neil Wilkes
Re: Bad Audio after transcoding
on Oct 2, 2006 at 2:30:33 pm

Drop the stereo file into an audio editor, Audition, WaveLab, Premiere, whatever you have, and run a plugin that will check the mono compatibility for you.
There is a free one at http://www.kellyindustries.com/stereo_tools.html
Just insert it into the master output buss and press the mono button.



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