On 13/11/15 15:33, David Rowe wrote: > The SM1000 drivers for the various audio ports already work in full > duplex. However there may be a CPU load issue to run full duplex, in > which case further code optimisation would be required.
Indeed, I tried full-duplex audio on the SM1000, seeing if I could take the microphone audio input and feed that back to a headset to give me an eyes-free indication that the PTT was on, but couldn't find a way to collect samples and do the software mixing in an acceptable manner. By far though, the biggest challenge will be cramming 1600bps audio down a GSM voice CODEC. The human ear cannot detect phase, and is poor at detecting amplitude and frequency. Add to this the fact a voice CODEC is attempting to simulate the human voice and how well humans typically can "whistle" modem tones (that is, not well), it is little surprise that trying to do data comms over this link is proving to be a major challenge. 1200bps is *really* pushing it. 700bps will be easier, however last time I tried FreeDV 700bps, the SM1000 crapped itself when I switched to DV mode. (And yes, it's time I pulled my finger out and did some more on the SM1000.) -- Stuart Longland (aka Redhatter, VK4MSL) I haven't lost my mind... ...it's backed up on a tape somewhere.
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