MP3's are encoded at bit-rates (quality settings) anywhere up to 320 kbps. 320 is the maximum & best quality & also the largest in size. eg: at 320 kpbs each minute of the song will be about 2.3 MB in size, whereas at 192 kbps one min is about 1.4 MB. 128 kbps will be even smaller. Anything less than 128 kbps will not be so good in sound quality.

Encoding may use Constant Bit Rate or Variable Bit Rate, with VBR reducing the size slightly. Some music may be encoded using joint stereo which is where the specific sounds that appear in both left & right at the same moment are encoded as mono & thus saving a lot of space. But sounds that aren't equal L & R are left as stereo. (In my experience it can make a difference to 'Head Room' when playing back thru headphones.)

Other forms of reducing size that are used other than mono are sample rate. And reducing top/bottom frequencies using filters.

If you wish to edit an mp3 then I'd recommend Audacity (free) which can import mp3's & wav/aiff & export into mp3's & wav/aiff formats. You will need to download all parts, manual, program, plug-in enabler, etc. of this program. It's editing functions are fine. Not bad for a free program & arguably as good as a $500 audio editor (except a little slower!)


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