[Icecast] Questions on setting up icecast

Geoff Shang geoff at hitsandpieces.net
Fri Sep 24 22:15:29 PDT 2004


JLB wrote:

> What's the difference between bitrate and samplerate? Samplerate is like
> 44KHz or 48KHz?

Yes.  Sample rate says how many samples of the sound are taken per second. 
The bit rate is how many bits are used to store a representation of those 
samples.

Lets use an example.  Suppose we have three files, all at 64kbps.  One is 
44.1kHz mono, one is 22.05kHz stereo and one is 22.05kHz mono.  Now, all 
use 64000 bits per second to store the sound.  The 22.05kHz mono file 
should, at least in theory, be the most faithful reproduction of the 
22.05kHz sound, since it's using the same amount of data to compress half 
the sound of either of the other two versions.  The 22.05kHz stereo file is 
using the same amount of data to compress two channels, so the amount of 
data per channel that is available is less, resulting in a lower quality 
representation of that 22.05kHz sound.  The 44.1kHz signal has twice the 
resolution of the 22.05kHz signal, but again is only using the same amount 
of data.  It's like trying to squash a picture that's twice the size into 
the same amount of data - it can be done, but depending on how well that 
compression works, the result mightn't be very good.

Streaming formats are always a compromise between sampling rate and bit 
rate.  If you're wanting to set up a stream for a modem listener, you need 
to ask yourself - do I want the highest sample rate possible knowing that 
it might not represent very well, or do I want a lower rate which will 
reproduce better, or maybe do I want a stereo stream versus a mono one.

Geoff.



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