File size became bigger

Special Interest Groups Audio Processing
1

Hi,

I used Audacity tu shorten an MP3 file from 3 hrs to 1 hr but I’m surprised that the file size for the 3 hrs is smaller than the 1 hr file. why is this happening?

2

You didn’t really shorten up a three-hour show.

You opened the show up in Audacity which converted it to an uncompressed WAV file (internally) for editing. Then, when you were finished, Audacity converted the show back to MP3. The conversion back to MP3 follows the rules in the lame encoder and they can compress to any value you want. In Audacity 1.3, you can do it at the export step, in 1.2 you have to do it in Audacity Preferences.

We warn people that MP3 damages the sound and the damage is cumulative and permanent. You will find that the new, smaller show sounds funny and bubbly compared to the old one. And that show sounds funny compared to the original production master at the studio. The damage is worse the smaller the file size.

Higher than about 300, most people can’t hear the damage. Around 64 for a stereo show, almost everybody can hear some problems. Below 32 is voicemail quality.

Koz

3

There are programs out there that can directly edit an MP3 file without recompression. I don’t know if they can resample after editing without damage.

Google time.

Koz

4

Dear koz,

Can you explain how to compress when u said “in 1.2 you have to do it in Audacity Preferences”. I don’t know how to do it.

I tried a few editing programs but I find that Audacity is simpler to use.

5

If all you want to do is shorten an MP3 file, try “MP3Split” http://mp3splt.sourceforge.net/

6

hi Steve,

I’m not splitting the file into smaller peices. I need to delete portions in the file that I don’t want to listen.

7

Assuming you’re on a PC (you didn’t say)…

Edit > Preferences > File Formats > MP3 Export Setup > (Pick your encoding number) > OK.

I would restart Audacity to make sure the change sticks.

Try several several numbers and listen to the show on a good sound system or good headphones. There’s no absolute rule about how good it’s going to sound – especially since you’re starting life with a damaged master. All these tools works very, very well if you start with a perfect capture file – like you personally sang into a microphone and captured it. They work a good deal less well if you have a fuzzy show to start with.

You still should find an MP3 cutter program that doesn’t need to recompress.

Koz

8

Thanks Koz.

By the way I’m using a PC.