[icecast] bitrate for slow modems

Geoff Shang gshang at uq.net.au
Thu Apr 5 21:53:09 PDT 2001



On Fri, 6 Apr 2001, John Griffiths wrote:

> ok so 24kbps for 56k modems...
>
> can i go any lower and get the 28 k modems? (still a lot of them about) or will 24 be good enough fo that?

As others have said, 16kbps should do the trick.  Keep in mind though that
the quality of the sound will also depend on the sampling rate.  MP3 will
handle some higher sampling rates higher than some of the lame defaults.
For example, 16kbps 11khz mono sounds very reasonable.  At 24kbps, either
22khz mono or 11khz stereo sound pretty good, though the latter is a bit
iffy under lame.  At least with 24kbps however, these aren't the lame
defaults.  Mono will give you 16khz and stereo gives you a lowly 8khz
(yuck!).  You can get lame to do higher sampling rates by using the
resample argument rather than letting it decide where to resample to.  You
can also improve sound quality by fiddling with the lowpass filter (IMHO,
it can be a bit conservative and can do with being raised a bit at times).
As a final tip, if you're encoding in mono, try out the experimental voice
mode, it might actually make things sound better (e.g. 24kbps 22khz mono
with --voice sounds pretty good).

Geoff.

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