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MP3 problems, also mac vs PC compatibility issues

 
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Tom Test
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Joined: 23 Jan 2007
Posts: 629
Location: Chicago, IL

PostPosted: Thu Mar 05, 2009 1:50 pm    Post subject: MP3 problems, also mac vs PC compatibility issues Reply with quote

Hey there,

Have you been following the mock audition I've been staging in the Chat forum? Well I finally pieced all 34 submissions together and posted a link to download the master file. But I am crestfallen at the horrible audio quality I now have, and I don't know why it happened.

Question: when I open an MP3, add a bunch of other MP3s, the save and close that file - THEN repeat the process a few times - am I making a compresssion of a compression of a compression every time I add new files and save it again? That's the only explanation I can think of.

If you want, PM me and I'll send you a short snippet of the file in question to your e-mail address. It sounds very artifact-y and echo-y. Craptacular.

Also, I had some strange issues with a few files from people who recorded on Macs. For some of them, when I tried opening their MP3 and adding it to the master file of all auditions, I'd get an error message telling me that the files from Mac users had a different sample rate that the file I was trying to add it to. But...I'm not so sure they really DID have a different sample rate (I requested 44.1 MP3 @ 128kbps). My Sound Forge 9.0 told me I could resample the Mac-user file, but it didn't work - or maybe I just can't figure out how to do it).

I figured out a work-around. I opened the mac-user MP3 file, saved it as a wav file (when I tried, the dialog box said it was a 48 Hz file by the way), saving it to 44.1, THEN convert it to MP3 @ 128. No resampling was done directly by me. I expect the issue is some Mac-vs-PC problem, and I hope someone can help me figure it out so I can avoid jumping through hoops.

Thanks for your help! I've put a lot of time into this mock audition, and don't want to disappoint a lot of people.
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ccpetersen
With a Side of Awesome


Joined: 19 Sep 2007
Posts: 3708
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PostPosted: Thu Mar 05, 2009 2:01 pm    Post subject: Reply with quote

Can't speak to the Mac mp3 problem, but yes, you can get that artifacty sound when you keep re-mp3-ing files together over and over. A recent project I did had that very problem. I sent a clean .wav file (provided by the studio where I recorded it with a slight bit of compression) off to a person who was going to make it part of a larger project she was doing for a group of educators. The final project was awful sounding and not the fault of those of us who had contributed relatively "clean" files. She was aghast at what happened, but not being familiar with audio, had turned it over to an engineer friend of hers.

It turned out the engineer had glommed several mp3s together to make File X and then glommed two more mp3s onto File X, mp3-ed that to make File Z, and then did the same thing to File Z with yet another new file. The final result had tons of compression, made the music sound warbly and the voices sound like the speakers were talking inside a huge can. There were these strange "whistling" artifacts, almost as if someone had broadcast the file and then made an mp3 of the broadcast.

So yeah...
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Jeffrey Kafer
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Joined: 09 Dec 2006
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PostPosted: Thu Mar 05, 2009 2:03 pm    Post subject: Reply with quote

Ditto what CC said. Stay in the world of uncompressed wav or AIFF until you export the final thing in MP3.
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ccpetersen
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PostPosted: Thu Mar 05, 2009 2:22 pm    Post subject: Reply with quote

This compression thing is why I submitted my "try" at the audition project in uncompressed .wav format.
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Tom Test
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Joined: 23 Jan 2007
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Location: Chicago, IL

PostPosted: Thu Mar 05, 2009 2:26 pm    Post subject: Reply with quote

Thank you, thank you, THANK YOU CC and Jeff!!!

So now I'll have to trash what I did and start over. Pain is the best teacher, right? Look for the new master file Friday around noon.
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bobsouer
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Joined: 15 Jul 2006
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PostPosted: Thu Mar 05, 2009 2:43 pm    Post subject: Reply with quote

Tom,

An alternative possibility would be to take all of the MP3 files, convert them to WAV files, then assemble everything as one huge WAV file and finally convert that final WAV file to your ultimate MP3.
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georgethetech
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PostPosted: Fri Mar 06, 2009 12:23 am    Post subject: Reply with quote

Yes, work in WAV, export in MP3. Convert all incoming files to WAV before working. It starts to remind of you the way it sounds when you make a cassette dub of a dub of a dub...
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Tom Test
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Location: Chicago, IL

PostPosted: Fri Mar 06, 2009 11:31 am    Post subject: Reply with quote

I took your advice George, and converted all the MP3 into WAV, added to the master file, then saved as MP3 when finished. Not it sounds great, though it took my entire morning. Well worth the effort.

Thanks to all for your help on this!!
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