Skip to content

Primer on digital voice

Southgate provides a Video of Codec2 presentation. It is a presentation (40+ minutes) by David Rowe, VK5DGR at the in Ballarat, January 16-20 2013.

“Codec2 is an open source low bit rate speech codec designed for communications quality speech at around 2400 bit/s. Applications include low bandwidth HF/VHF digital radio and VOIP trunking. Codec 2 operating at 2000 bit/s can send 32 phone calls using the bandwidth required for one 64 kbit/s uncompressed phone call. It fills a gap in open source, free-as-in-speech voice codecs beneath 5000 bit/s and is released under the GNU Lesser General Public License (LGPL).”

It turns out that HF speech oriented codecs run afoul of WMD export restrictions. That provides some indication of the value seen in the compression and encoding technologies under experiment.

Like jpeg for photographs, the idea behind Rowe’s work is to compress speech by utilizing a knowledge of how speech is formed. The presentation provides a good overview of the ideas behind developing software for this sort of effort.

The article in April QST on this sparked a lot of interest as well. Go to for more information and software. Tune in to 14.236 and listen for weird noises as that is currently the frequency most are using for experiments.

as for the WMD restrictions and FCC handcuffs on modulations, you need to check that as well as you certainly don’t want guys in paramilitary gear showing up at your doorstep 😉 ….

Post a Comment

You must be logged in to post a comment.