Large File Sizes

i’ve noticed something strange when importing sound into flash. the file becomes a lot larger than it should be and this has happened to me many times before. heres a scenario to describe what i’m talking about:

original file size: 900 kB
music file size(to be imported): 5000 kB

import the music file size, and it should be automatically compressed (usually i get a message at the bottom of the properties window for the sound, saying that it was decreased to 10-15% the size of the original file).
even without the compression, the file size shouldn’t be more than 5900kB (900 + 5000), right? well oddly enough, it isn’t. it might increase by 3 times this amount from what i’ve experienced in the past(to about 18 000kB).

this has caused many problems for me including the inability to upload files(due to upload limits) and slow file transfer, which is the reason i decided to bring this up.

ok, does anyone know the reason why this happens (file sizes increase greatly when importing sound)?