Hi James
I think you mean 320 kbps (Kilobits per second) rather then mbps (Megabits per second). If only!!!
(1k is 1000 rather then the normal software programmers 1024)
Digital Audio is measured in two ways: Bit Rate Resolution and Sample Rate.
Bit rate is the number of bits that are processed per unit of time or bits per second. bps. Sample Rate is the number of samples per second taken. 1Hz = 1 sample per second. RedBook CD is 44.1kHz = 44,100 samples per second.
Sample rate x channels x bit rate = kbps
44,100 x 2 x 16 = 1,411,200 bits per second (bps) = 1,411 kbps
This is where I may go wrong

if 1,411,200 / 2 / 16 = 44100 (CD audio)
then...
320,000 / 2 / 8 = 20,000 or +- 20kHz maximum sampling rate
Then again, internet streaming audio may be compressed (like MP3) so the actual uncompressed data will be larger and therefore quite close to CD quality.
Hope this helps.
A