undefined | Better HN

0 pointsAnimats5y ago0 comments

You need to maintain millisecond sync while the devices are widely separated, possibly for hours. Cell phone clocks are not millisecond-accurate over hours. The idea is that a group of people all download the app and walk or drive around the area of interest collecting time-stamped audio and sending it to a server.

Amusingly, data collection would be easier with analog technology. Get some VHS walkie-talkies, and, at the base station, feed all the channels into a multitrack tape recorder like musicians use. No sync problems.

0 comments

gpm5y ago

For sounds transmitted through the air, ms precision is really necessary at distances of more than a few meters. Network time should be close enough at 10s or even 100 ms (roughly speaking < 10 meters of error - which is good enough to set up a local monitoring net via wifi with <1ms/<30cm of error).

I guess this is complicated by the fact that the speed of sound through the ground is ~6km/s. Rather faster than the speed of sound through the air. Multiplying those errors by 20... but 200 meters of error isn't that bad. A powerful local network with no latency would then be enough to isolate further.

Anyways, turns out that you can get gps time on androids, so this should be solvable with much better latency https://stackoverflow.com/questions/7017069/gps-time-in-andr...

as-j5y ago

I think you’re missing how easy it is to do these days.

It’s pretty easy to do with NTP synced devices. I’m lucky enough to have a fleet of devices sync with GPS and the PPS signal. It’s pretty amazing to/fun to do latency tests, you grab a time stamp and ship it to far side and time stamp the arrival. Voila single direction latency measurements.

AnimatsOP5y ago

Sorry, VHF.

j / k navigate · click thread line to collapse