Voice over GPRS?

Knight Walker moko at kobran.org
Fri Feb 2 18:02:17 CET 2007

On Fri, Feb 02, 2007 at 11:37:59AM -0500, ROB wrote:
> Bit rate=sampling rate x bit depth
> 1kb/s isn't going to get you too much audio.  Try encoding an mp3 at
> 1kb/s to see how audible that would be.  I think you'd be looking at
> something more along the lines of 32-64kb/s to get anything that you
> could understand.  It might be easier to make a phone call.
> Conveniently enough, I think the device will have that capacity as
> well.

MP3 isn't for voice audio, it's for music audio (Which has a larger
dynamic range and needs more resolution than voice-only audio).  For
voice-only audio, you'd be better served by a codec like Speex; one
that is designed specifically for human speeking vocal range.  I've
heard completely understandable Speex recordings at about 8kb/sec.
They didn't sound that great, but I could understand them.

Going back to the original post, I'm not sure even Speex could help,
as the biggest thing is going to be the latency of the audio.  Cell
phones have a bad enough lag just using the regular methods, but if
the latency gets up over a second, then you'll be stepping on each
other's side of the conversation.


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