What is the quickest, easiest way to compress an MP3 file?
The archivers with the highest compression ratio would be KGB (which has been used to compress a 430 MB MS Office ISO image to fit on a floppy disk) and Uharc (a high compression multimedia archiver), but they're not necessarily the fastest. The compression will be lossless.
If you want to reduce the size via the bitrate (and thus the quality), I recommend this program:
MP3 Quality Modifier makes it really easy to change the bitrate of your MP3 music collection so that the filesize can be dramatically reduced. With this advantage it's possible to put more music on your MP3-player or just to save some disk space. Even advanced tasks are possible: Downsampling, changing the used channels and so on. With the included presets it's simpler than ever before to manage all those settings.
Best of all is that - unlike other software - the ID3 tags (title, album pictures, etc.) will be completely retained without any effort!
Main features:
* Change MP3 quality with just a few clicks.
* Really easy and intuitive interface.
* Retain all ID3 tags with ease.
* Advanced options: detailed bitrate settings, sample frequency, etc.
* Quality comparison: compare created files with original ones.
* Multilingual: English, French, German, Italian, Portuguese, Spanish.
* Portable: extremely small, just one executable, no installation.
* Free of charge!
All programs are freeware and portable.
And if you want to learn more about audio ripping and MP3, here's a very comprehensive tutorial:
Radified Guide to Ripping CD audio & MP3 Encoding
As MP3 files are already compressed - in much the same way that JPEG images are compressed - simply adding it to a ZIP archive won't compress it any further as there is no redundant data to remove.
To reduce the size of an MP3 file you'll have to re-encode it at a lower bit rate using something like Media Monkey. This will result in a loss of quality; it would take the bit-rate too low. Media Monkey supports filtering and batch operations so you can select the files you want to re-encode and perform the operation in one go. This will also preserve any tagging you might have on the file. However, re-encoding an already lossy file will result in worse artefacts than you'd get by going back to the original source and encoding that at lower bit rate. You can demonstrate this effect by taking a JPEG file and re-save it several times reducing the quality each time.
Another thing to check is to ensure that any cover images are stored outside the MP3 file. Otherwise for an album of 12 tracks you'll have 12 copies of the same image.
Use lame from the command line (executable can be found here; there's also a tutorial on the command line options). Choose whatever settings you like best to reduce the size of your file; try using VBR (variable bitrate) and a bitrate of about 128 kbps. It should be more than enough to keep the audio quality to within normal limits. Listen to the mp3 and determine if it's ok.
Just try going as low as you can while still maintaining at least some audio quality (use 64 kbps and check the output). The sound volume of the mp3's will get lower and lower and you'll lose most of the richness of the sound.
Here's an example of how to use it:
lame -b 64 -h -V 6 input.mp3 output.mp3
This will encode it to 64 kbps (variable bitrate).