Shrink MP3 file

Can I shrink a MP3 file in Audacity?

If yes,what would the steps be?

The file size of any compressed file* is directly related to the bitrate and playing time. The bitrate kbps is kilo_bits_ per second, so if you know that there are 8 bits in a byte:

File size in kilobytes = (Playing Time in Seconds x Bitrate in kbps) / 8

For smaller files, when you export to MP3 use a lower CBR bitrate, or choose a lower quality VBR (variable bitrate) setting. Note that VBR 0 is the “best” (highest variable bitrate) and VBR 9 is the most-compressed (lowest variable bitrate).

If you haven’t done so already, you’ll need to install the optional LAME MP3 encoder.

If you are just re-encoding the MP3 without editing, try [u]TAudioConverter[/u]. Once you set-up the output format and the output file location, you can just drag your files into TAudioConverter and click “Start”.

Shrink MP3 file

If you have the original uncompressed file, start with that. Since MP3 is lossy compression, it’s best to compress to MP3 once if possible.


  • It’s true for uncompressed files too, but uncompressed files are not normally specified by bitrate… Usually, we talk about the sample rate, bit-depth, and number of channels. From that, you can calculate the bitrate if you wish.

Yes, but you may not want to. You take a quality hit no matter what you do. Audacity has to make a new MP3 with normal quality damage, so even if all you did was pull an MP3 in and Export it immediately at the same quality, it will be half as good.

The best way to get half the filesizes is transform from stereo to mono. Instant half size files.

If you want to do it in MP3 quality settings, File > Export: MP3, Options, Quality. Pick a quality setting lower than what you had. Audcity has no Clip INFO tool, so you have to know ahead of time what you had.

Fuzzy rules are 32 for a mono show and 64 for stereo. That’s only starting with perfect WAV or CD work, not another MP3. If you start with an MP3, the actual sound quality will be a combination of the old and new quality.


The best way to get half the filesizes is transform from stereo to mono. Instant half size files.

Not with MP3… A 128 kbps stereo MP3 is the same size as a 128 kbps mono MP3.

The mono file of the same bitrate may have slightly better quality.

The default Joint Stereo option compresses the common left & right (L+R = M) information only once and the difference (L - R = S) once. The S channel can often use a lower bitrate so you can get equal quality with a file that’s bigger than a mono file, but smaller than an equal-quality separately-encoded stereo file.

I misspoke. Starting from the same perfect WAV quality, a 32-bit mono MP3 will sound the same as a 64 bit stereo.


When you say “32-bit mono” vs “64 bit stereo”, I presume that you mean “32 kbps” vs “64 kbps”.
There is no such thing as “32 bit” or “64 bit” MP3.

If the “perfect WAV quality” recording was a mono show, then a 64 kbps stereo version will almost certainly be noticeably clearer, assuming that “Joint Stereo” (default) is selected and assuming that you are able to hear above 8500 Hz.

If the “perfect WAV quality” recording was a stereo show, then (obviously) the 32 kbps mono version will lose all stereo information (the result is mono).

I appreciate the replies.

Here is what I have and am doing.

I have a bizillion mp3 recordings from a coaching program.
I want to make them small enough to load on one of
my websites so I always have them in case my computer
blows up.
I would like the quality to be good enough that I can
understand the voice.

What is the simplest way to accomplish this?

Spend some $'s on thumb drives or external hard drives. (32 GB thumb drives are currently available for under $15 US)

I think I have one kicking around the office. How much data can one
of those hold?


Old ones, not very much.

32 GB works out at as between 6 and 18 months of continuous music, depending on the quality.

I want to make them small enough to load on one of my websites

Just to be sparkling clear, you will not be loading “them” on another drive or your web site. You will be loading a lower quality version of “them.” MP3 works are brittle and all you can do is listen to them or maybe transfer them whole somewhere else. Not “making them smaller.”

MP3 is an end product, not a step in the middle of production.

Never do production in MP3.


I need about 4 gigs or more. The old one I have only goes to 450 megs.

They may not make 4GB any more.
Screen Shot 2015-03-16 at 21.40.09.png

Yes, thanks!

I found what I need. I can get a 16 gig stick for about $10.

Thanks, again!