Audacity Forum

I have some files about 45 minutes long in mp3 format which I would like to reduce the size of. The original files are 44100 sampling rate, 32-bit, and stereo. When I open one of these mp3 files in Audacity and change the file to mono, 22050, and 16-bit and write out the edited file, the file size is the same as the original. Please correct me if I am wrong, but I would expect that changing those three things would dramatically reduce the file size.

To change the file size, I changed the project rate in the bottom left corner.
To change the bit rate, I clicked on Mix button (the one with the downward-facing arrow) and selected Set Sample Format > 16-bit.
To change from stereo to mono, I again clicked on the Mix button and selected Split Stereo Track, closed one of the new mono tracks, and in the mono track that was left I clicked on Mix > Mono.
To write out the file, I selected the entire sound, and then clicked File > Export Selection as MP3.

I have LAME installed. I am using Audacity 1.2.6.

What am I doing wrong? How can I reduce the size of the file?

Thanks, Isaac

<<<To write out the file, I selected the entire sound, and then clicked File > Export Selection as MP3.>>>

Had you exported your show as WAV, the filesize would have gotten smaller--or changed.

Audacity isn't good with converting between standards, and you may not want to.

Most compressors including MP3 work by trying as much as possible to preserve the quality of the original. If you present a fuzzy, muffled, reduced bit rate original, lame will try to preserve the fuzzy and muffled. It will not necessarily result in a smaller MP3 show. The only way you can help is create mono ahead of a mono MP3, and I wouldn't be shocked to learn that you can do that at the MP3 creation step.

There is another item for consideration. Not everybody can play MP3 files created from 32-bit floating originals. A voice performer got into trouble a while back and I dug her out by resampling her 32-bit MP3 demonstrations so they originated from 16-bit masters. Suddenly all the clients could play them and she got the job.

We forum helpers are very nearly unanimous that most people should drop Audacity 1.2 as a hot rock and start using 1.3. I may have been the last holdout. Audacity 1.3 lets you manage the MP3 character at the export step, not in some buried preference panel like 1.2 does. As you found out, MP3 export file size depends first on its settings, not the size of the original.

Koz

[wrote the following before seeing Koz's response:] My understanding of this is rough, but I think bit depth and sampling rate don't really apply to MP3. MP3 has its own settings ("bit rate") that determine how big the MP3 file will be. And unfortunately, Audacity 1.2 only gives you limited control over this. To exert what control you can, see the bottom of the "File Formats" tab under preferences, and lower your bit rate. Audacity 1.3 gives you more control, including variable bit rate, which gives you higher quality with smaller file sizes.

That said, everyone agrees (I haven't tried it myself) that decoding and re-encoding MP3 files, or any other lossy compressed format, hurts quality a lot and should be avoided whenever possible. Use the original, uncompressed files if there's any way you can get access to them. --Allen

This is a little late in coming, but thanks for your replies. They were very helpful!