MP3 can be saved in many different “bit rates.” The higher the bit rate, the higher the quality.

You can take account of this: a bit rate of 16 and a sample rate of 44khz is CD quality.  For a 10 minute ‘cast, that’s going to create a file size of around 1.2Mb.

You really don’t need to go that high when saving a recording of the spoken voice. And you don’t need to be in stereo.

That keeps your file size down (it’s still going to be far more than you think, at least to begin with). It also means that you, and your listeners, are reducing the data capacity or bandwidth being burned which, for millions of people listening on a mobile phone, is a serious problem.

The same 10 minute file, at 8bit and 16Khz bit rate and saved in mono is going to be about 600Kb – that’s half the size.  That’s probably as low as you’d want to go in terms of quality.

Musician Colin Crawley has a very useful calculator which lets you jiggle about various settings and it tells you what your file size will be. His website is at www.colincrawley.com

When you look at Crawley’s page you will see that some file formats, e.g. WAV, create vastly larger files than MP3. But that’s only part of the reason we don’t allow them: it’s because not all players natively play WAV files but everything plays MP3.