Hi all,
(crossposted in digitalvoice@googlegroups and freetelcodec2@sourceforge. Follow-up set to the freetel-codec2 list). Today, I have been doing some work on the AFSK version of codec2 for VHF/UHF. One of the things I have been thinking about is how to implement signaling (like and end-of-stream event) in the DV stream. In c2gmsk, even the lowest 2400 bps version has sufficient bandwith do add marker whenever in the stream. For that reason, it is very easy to encode this kind of signaling information "out of band", i.e. in the syncronisation channel of the DV streamm In contrast, the c2afsk modem only has 1800 bps: in its current implementation 1400 bps for codec2 voice, 300 bps for FEC and a 100 bps for the syncronisation channel. However, this 100 bps syncronisation information is spread over multiple frames: it consist of 4 bits per 40 ms audioframe, so one complete "sync" pattern (24 bits) is spread over 6 frames, or 240 ms. For the process of syncronisation, that should not be an issue. However, this does make the syncronisation channel pretty much useless for signaling. So I am wondering if it would not be possible to encode a "end-of-stream" signal INSIDE the codec2 channel. For that, I would need to know if there exist certain bitpatterns in a codec2 audio-stream that should never be seen in a codec2 stream. We could use that then as a "end-of-stream" marker. Does something like that exist? Also, just wondering. Could something like this not also be used for encoding DTMF. As codec2 is a voice vocoder, it is probably not really good at incoding the native DTMF tones. If we want to be able to carry DTMF information in a codec2 stream, it might also be usefull to use some special encoding for this. Anybody ideas of other information that could perhaps be carried as inband information in a codec2 channel? What bitrate would it need? How to encode it? Any comments welcome! 73 kristoff - ON1ARF ------------------------------------------------------------------------------ Introducing Performance Central, a new site from SourceForge and AppDynamics. Performance Central is your source for news, insights, analysis and resources for efficient Application Performance Management. Visit us today! http://pubads.g.doubleclick.net/gampad/clk?id=48897511&iu=/4140/ostg.clktrk _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
