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Save As MP3 and file size

 
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AvatarKory



Joined: 08 Nov 2013
Posts: 4

PostPosted: Wed Feb 15, 2017 10:56 pm    Post subject: Save As MP3 and file size Reply with quote

Hi,

Due to an oversight on our batch processing, we were loads large (>50MB) MP3 files, and without making any changes to the file, saving the audio again as an MP3 but with a different file name.

I was able to manually reproduce this effect:

-rw-r--r--@ 1 kory staff 57658895 Feb 15 13:22 TL.mp3
-rw-r--r--@ 1 kory staff 57658895 Feb 15 13:24 x1.mp3
-rw-r--r--@ 1 kory staff 57922335 Feb 15 13:26 x2.mp3
-rw-r--r--@ 1 kory staff 57793449 Feb 15 13:29 x3.mp3

So the original file we digitized from tape with Amadeus Pro 2.3.1 is TL.mp3. We then saved TL.mp3 as x1.mp3. We closed x1.mp3, re-opened it, and saved it as x2.mp3. We then closed x2.mp3, re-opened it and saved it as x3.mp3.

So this brings up some questions:

1. Why does the file size keep changing? First it grows (x1 -> x2), then it shrinks (x2 -> x3). I realize that MP3 is a lossy compression, but I would expect it to be more consistent.

2. Will I lose audio quality each time I open and then save an MP3 file? We have hundreds of very large audio files that we are processing. We are doing the processing a single step at a time across all of the files, then we do the next step. The reason we are doing it this way is that we are making adjustments to our process along the way. If I am losing audio quality every time I save the file as MP3, I wonder if I should be saving them as FLAC, for example, until all of the processing is done for each file.

Thank you very much for any help that you can provide!

Regards,
Kory
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Martin Hairer
Site Admin


Joined: 08 Nov 2006
Posts: 1605

PostPosted: Wed Feb 15, 2017 11:54 pm    Post subject: Save As MP3 and file size Reply with quote

Hi Kory,

Quote:
1. Why does the file size keep changing? First it grows (x1 -> x2), then it shrinks (x2 -> x3). I realize that MP3 is a lossy compression, but I would expect it to be more consistent.

Whenever you open an Mp3 file and save it to a new file, it gets reencoded. At this stage, if you use variable bitrate encoding (VBR or ABR) there's no reason the new file should be of the exact same size as the original, a fluctuation of half a percent or so is perfectly normal. If you use CBR you should get 100% consistent file sizes, but there's no reason to do this unless you have to.

Quote:
2. Will I lose audio quality each time I open and then save an MP3 file? We have hundreds of very large audio files that we are processing. We are doing the processing a single step at a time across all of the files, then we do the next step. The reason we are doing it this way is that we are making adjustments to our process along the way. If I am losing audio quality every time I save the file as MP3, I wonder if I should be saving them as FLAC, for example, until all of the processing is done for each file.

Yes, you should use a lossless format like AIFF, FLAC, or Amadeus's own format for intermediate copies as you will definitely lose quality every time you reencode an Mp3 file. Regards,

Martin

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http://www.hairersoft.com/
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AvatarKory



Joined: 08 Nov 2013
Posts: 4

PostPosted: Thu Feb 16, 2017 10:01 pm    Post subject: Reply with quote

Thank you, Martin. That was very insightful and helpful. I have one more quick question. I think I know the answer to this question, but I am hoping I am wrong:

Is there a way to save just the Amaeus session information (such as playback position, markers, selected sections, etc) to a file?

Some of these audio files are very long, and if we don't finish processing them in one day, we want to be able to pick up where we were the next time we are reviewing ang editing the audio files.

Thanks,
Kory
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Martin Hairer
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Joined: 08 Nov 2006
Posts: 1605

PostPosted: Thu Feb 16, 2017 10:10 pm    Post subject: Save As MP3 and file size Reply with quote

Dear Kory,

Quote:
Is there a way to save just the Amaeus session information (such as playback position, markers, selected sections, etc) to a file?

Markers are preserved by several formats (like FLAC, AIFF, Amadeus Pro), but I'm afraid that no format preserves playback position and selection. The format that preserves the most attributes and is the fastest to open / save is Amadeus Pro's own native file format, so this would be a natural choice for saving intermediate copies. Regards,

Martin

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HairerSoft
http://www.hairersoft.com/
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