Yes, I read that post about calibration procedure. Idea is to take quartz watch as reference and compare it to sound card, because sound card is not so accurate (also described in that post). I'm just little confused about mentioned "correction procedure" of quartz watch, because it goes usually fast +10 s/day. So what is the real accurate reference? What is the result of calibration procedure ? Is it diff between quartz clock and sound card clock?
If so, we can use digital metronome too, they are declared as accurate, they usually have audio output, adjustable beat rate etc...
The reason I'm talking about whole this stuff is:
conventional timegraphers are usually calibrated in factory to same reference timing source, so they will all have very similar results. They also have same sound pickup method, so inputs in state machine are pretty solid, right? So you can expect similar results with some small error rate...
TG is excellent idea, ingenious algorithm, it should be used to it's limits. If we don't have sort of standardized pickup and time reference, we can not compare results precisely, right?
I'm thinking of running it on dedicated platform (RPI3 with some Linux, even better try would be Android tablet (ARM or x86) with some Linux distro), so now I'm picking up best practice tips regarding sound pickup and calibration.
I know it can be done via GPS, for example, have to study it in more details... But I think it would be overkill, because result values are not in that precision range as GPS time reference.
Building some stable oscillator reference would be "long road" too, even if I'm sure there must be some ready modules out there... So I'm trying to get best effort reference.
Pretty much we have excellent product here... Imagine you can have this software running on some embedded platform (like RPI or similar). It is affordable, you know what is "inside", it is upgrade-able etc.
So, open questions like sound pickup and calibration would be 99% of that road.
I' not speaking about price. If you compare price of RPI+Sound Pickup+Some Display+Miscellaneous stuff, it is similar to cheap timegrapher machine from Far East... But it is huge difference if you build it, you can debug it, upgrade, service etc... Not to mention contribution of members of such a large community of watch hobbyist and enthusiasts.
Thank you, please share your thoughts.