Hi Albert,
On 12-04-13 17:14, Albert Cahalan wrote: >> Well, that is true if you assume that the USB audio-dongle supports stereo. >> >> One of the things about GMSK is that the best result is got using cheap >> USB devices, this because of the lack of low-pass filters on the input >> and output. However, you would be surprised to see how many of these USB >> audio-dongles only support capturing in 1 channel! > If it only supports mono, you're wasting power and space. I don't understand this. Both the GMSK signal and the voice signal are mono. > The low-pass filter should be passing everything below about > 22.05 or 24 kHz, right? Even an imperfect filter should be fine. From what I understand from the people of free*Star who have done tests with different audio-dongles is that a number of them also filter on the low-part of the audio-spectrum. >> Another issue is that voice-capturing/playback is done by a different >> application that does GMSK modulation/demodulation. This was a very >> explicit choice to have a additional level of flexibility so that audio >> / codec2 encoding (which needs a FPU) can be done by a different device >> then the GMSK modulation (which can be done without FPU). > I hope you can #if this away. Concidering these are two different packages, this would be a bit difficult :-) I always liked the unix way of working: write "tools" that do one particular part of a job (and do that good). Next, design "applications" by glueing one or more of these tools together. >>> Alternately, you could be compatible with fldigi's PTT circuit. >>> This circuit keys the transmitter via a 1 kHz tone in the right >>> audio channel. This type of keying has the advantage of >>> matched latency; the PTT signal doesn't arrive at the radio >>> long before or long after the modem output transitions. >> That would indeed be an interesting option. > The comment about the modem output itself driving the circuit > is interesting. True, as said, feel free to implement it and upload the code to github. > That would seem to take away any ability to > adjust relative timing, but maybe there could be a preamble. I don't understand this. What exactly do you mean by this? >> For PCs, that I think not such an issue. Most of them have more then >> sufficient USB ports; so simply use a USB-to-serial adapter. > USB adds latency. It's also not likely to match the audio latency. Euh ... I don't understand your remark about "match the audio-latency". The demodulator simply grabs a piece of audio (40 ms) and demodulate it and then tries to decode it based on its state in the c2gmsk protocol. What exactly does latency come into this? 73 Kristoff - ON1ARF ------------------------------------------------------------------------------ Precog is a next-generation analytics platform capable of advanced analytics on semi-structured data. The platform includes APIs for building apps and a phenomenal toolset for data science. Developers can use our toolset for easy data analysis & visualization. Get a free account! http://www2.precog.com/precogplatform/slashdotnewsletter _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
