Hello List, I am also intrigued by the wideband possibilities for Codec 2 over narrow HF digital radio channels. I was brainstorming this with Bruce and Jean-Marc recently.
As Jean-Marc points out, there is some more spectral information above 4kHz. For example a few more peaks and troughs in the speech spectrum in the range of 4-8kHz. This would require a higher LPC order, and over the channel a few more LSPs. The good news is that the ear is not very sensitive to this information, so it can be encoded fairly coarsely at a low bit rate. No extra bits are required to encode more harmonics or voicing for wideband audio - we would just extend the harmonics out to 8kHz, setting the amplitudes based on the LPC envelope. So for a few hundred bit/s more we could probably get a Codec 2 running at a 16 kHz sample rate: i.e. an "AM broadcast" audio bandwidth of between 50 and 7000 Hz. It wouldn't sound as good as an audio codec like Opus (or wideband Speex). But booming bass out of a Ham radio might be an interesting. Curiously, this could all be sent over a regular HF Ham radio SSB "channel" using say 2kHz of RF spectrum, and might only require 1dB more power. Cheers, David ------------------------------------------------------------------------------ Keep Your Developer Skills Current with LearnDevNow! The most comprehensive online learning library for Microsoft developers is just $99.99! Visual Studio, SharePoint, SQL - plus HTML5, CSS3, MVC3, Metro Style Apps, more. Free future releases when you subscribe now! http://p.sf.net/sfu/learndevnow-d2d _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
