There is always a difference between the audio quality we would like to reach and the minimal bandwidth requirements for radio streaming. Assuming that downstream is in most cases bigger than upstream, it is the broadcaster to decide at which bit rate he/she will transmit audio data.

An optimal requirement would be: stereo streaming, 44kHz at 128Kbps in .ogg or .mp3 format. That needs an upstream connection of about 150Kbit/s (19KB/s): 128 Kilobits per second upload for the radio stream itself, and still some bandwidth free for other services, like an IRC chat and web browsing. In this case we guarantee a good audio quality, and the streaming client listening to our transmission, will still have enough bandwidth free for usual Internet surfing while listening to our radio (128Kbit/s = 16KB/s downstream, 33% of a normal DSL connection 50KB/s downstream).

A minimal requirement for acceptable music quality would be: stereo streaming, 22kHz at 56 in .ogg froman, 22kHz at 64Kbps in .mp3 format. The upstream connection needed is, in this case, about 80Kbit/s (10KB/s), leaving some upstream space for other applications. In this case the streaming client would receive a clear audio signal, very compressed but still accettable, and consumes only 64Kbit/s = 8KB/s downstream for radio listening.

Of course we could go lower than this, especially in case of a pure speech transmission, but remember: below the 56Kbps border the music quality will be very, very compromised!

An acceptable speech quality can be reached already by stereo 11khz at 32Kbps in .mp3 format. Being only speech we could also focus on mono quality instead of stereo. In this case, while our upstream margin needed is around 40Kbit/s = 5KB/s, haveing an IRC chat service running inside that margin, the streaming client would receive clear speech audio by 4KB/s downstream.

Feedback is very important if we are broadcasting, and even more important if our broadcast faces an upstream bottleneck. Before going "on air", we should perform some technical broadcasts at different bit rates, with a client listening and, as an example through an IRC chat, telling us how audio quality "on the other side" gets influenced by the different rates we choose: through the client's feedback we will base the bit rate decision for our effective broadcast.

A simple bandwidth online tester is the commercial one from arcor.de (in german). Here you will be able to test online the downstream and upstream margin of your actual connection.