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

Jean-Marc Valin jmvalin at jmvalin.ca
Wed May 22 05:11:16 PDT 2013


I suggest you have a look at David Rowe's codec2.


On 05/22/2013 07:31 AM, Hans Freitag wrote:
> 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
> Codec?
> 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 
>       Hans 

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