Shorter file, but greater in size than original!

I have just removed extraneous music of up to 1.5minutes in length from 12 recordings, but the files have grown in size, one has gone from 17Mb to over 25Mb!

Can anyone tell me how I can ensure that future edited (shortened) files remain at their original or smaller size? I exported them with the pre-set options.

Baffled in France!


If you’re just cutting and shortening a show or production, you can use a “pure” MP3 editor which doesn’t have a size change. They won’t do much else, but simple cutting is good.

If you stick with Audacity, you have a problem. Audacity always makes a completely new MP3 when you export. That means you’re a total slave to the export settings completely divorced from the import settings. That’s why the file got larger. You would have to know the original file specifications before you start.

But that’s not recommended because every time you make a new MP3, the compression distortion and damage goes up. Your work may suddenly start to sound like singing into a wine glass. You can prevent the extra damage by making a much higher quality MP3…and a much larger file.

And this in one short post is why you never, ever do music or entertainment production or editing in MP3. Do everything in perfect quality WAV and convert to MP3 as a last step if you have to.


If you know the bitrate and you know that bitrate is kilobytes per second (kbps) or megabytes per second, and if you know there are 8 bits in a byte, you can calculate file size.*

File Size in bytes = (bitrate in kbps x 1000 x Playing Time in minutes x 60) / 8

Or with uncompressed files if you know the file-details -

File Size in bytes = Sample Rate in kHz x 1000 x (bit depth/8) x Number of Channels.

You can also calculate the bitrate for uncompressed files. For example “CD quality” WAV files are 16-bits, 44.1kHz, 2-channel stereo. That works-out to 1411kbps (about 10MB per minute).


  • The calculations are approximations. They don’t include file headers, tags (artist, album information, etc.), or embedded images (album artwork).

I am totally indebted to you both for not only taking the time to read and reply to my query, but to enlighten me with such detail. Whilst I would candidly suggest I’m not totally ignorant in most aspects of computing, I truly had no idea about the shortcomings of mp3 files with respect to exporting and its resulting loss of quality - somewhat akin to jpg files.

Thank you both sincerely.

That’s a good analogy.