Hi all,
With help of some people, I am now working on the 2400 bps GMSK modem for codec2. The advantage of this modem is the small bandwidth which -in addition to an advantage by itself on certain bands- also should give a db better S/N ratio. This mode is only possible due to the fact that codec2 actually runs very well at 1400 and even 1200 bps and does not need 2400 bps. Now, for this modem, there are two options: - use the 1400 bps codec and use either no or limited FEC (depending if there sync/data information alongside the voice channel) - use the 1200 bps codec and use a better FEC (FEC 2/3 or 1/2) So, what do you think of the 1200 bps modem? Does anybody have any experience with it? Does anybody see any reason not to use it? (based on practicle experience) If we use the 1400 bps modem, the format of a 40 ms frame (96 bits) could be like this: - for frames with sync or additional data 24 bits sync or data 56 bits voice 16 bits spare (perhaps use it with some FEC mechanism to protect part of the header) - for frames without sync or additional data 56 bits voice rest: FEC (still do be descided how) If we use the 1200 bps modem, the format of a 40 ms frames (96 bits) could be like this: - for frames with sync or additional data 24 bits sync or additional data 48 bits voice 24 bits FEC (FEC rate 2/3) - for frames without sync or additional data 48 bits voice 48 bits FEC (FEC rate 1/2). So, from this point of view, using the 1200 bps codec would have a clear advantage; so -hence- the question if somebody has some practicle experience with the 1200 bps codec or see any reason not to use that codec. 73 Kristoff - ON1ARF ------------------------------------------------------------------------------ Everyone hates slow websites. So do we. Make your web apps faster with AppDynamics Download AppDynamics Lite for free today: http://p.sf.net/sfu/appdyn_sfd2d_oct _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
