[Speex-dev] is it possible to bring speed below 1000 bit/s

Hans Freitag zem at fnordpol.de
Wed May 22 04:31:06 PDT 2013

Hi folks, 

I am totally new to audio streaming codecs, and just looking around. Trying to
figure out what else I can put on top of my very long list of projects. 
So a few days ago I figured out that fldigi a digimode application for Amateur
Radio supports a dual 1000 Baud PSK mode. I thought "that's fast" and started
looking around which sort of Data I could put into that. 

A typical ssb Voice signal has a bandwidth of about 1.9 to 2.4 KHz round about.
The shorter the bandwith the more a signal can reach. 

So I started wondering if it is maybe possible to compress a voice signal down
to a bandwith of 1000 KHz which would be a PSK 1000 mode with a fully open

The only thing I found so far is MELP (800 Bit/s), but, according to Wikipedia,
it has some Patent rights so it can't be used freely. The only melp code I
found so far available for download only has some Microsoft Developer Studio
build information.     

So far, speex has a bandwith of 2150 Bits/s. Which is almost below the 2kBit/s  
border. So far of course I am also thinking about making the channel wider 
or improving the Modulation, and about the whole 
Quality/Fault-tolerance/Bandwith thing. 

So, what do you think? 

best regards 

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