I would like sub-millisecond timestamps for a mono audio radio signal that I have in the shack. The timestamps could be continuous (Every sample) or just every "frame" where maybe a frame is a second to a minute. I would like to calibrate both the absolute time as well as the delta time between samples based on the timestamps. (I would expect that say a nominal 48kHz sample rate would be off by many tens of ppm because of crystal tolerances.). I have a both Windows and Linux based PCs running Audacity with a local GPS-based LAN refclock and ntpd. I trust the ntpd time to be stable to the sub-millisecond. Can Audacity do this kind of timestamping for me based on the system clock? Or should I, say, take the PPS from a GPS, and feed it into channel 2, with the audio going into channel 1, and make a stereo recording? I suppose I could then manually label the filename with the second the recording was begun. There would likely be some delta (maybe half the sample interval?) between the two channels but I'm fine with that as long as it is at the sub-millisecond level. Tim N3QE

	Attila Kinali

On Sat, 31 Mar 2018 10:41:45 -0400 Tim Shoppa <tshoppa@gmail.com> wrote: > Can Audacity do this kind of timestamping for me based on the system clock? I don't know about audacity, but writing a small program in c that reads from the soundcard and does the timestamping is pretty easy. Should be less than 50 lines of code, with error checking and all. You can use [1] as a decent starting point. One important point: Switch off all other applications that access the soundcard, as some of these are pretty nasty when it comes to their behaviour. Especially pulseaudio is known to mess with all kinds of settings while running.... Oh, and don't even try to run anything ontop of pulseaudio, it is known to mess up audio timing by several 10ms, sometimes even over 100ms. Attila Kinali [1] https://gist.github.com/albanpeignier/104902 -- <JaberWorky> The bad part of Zurich is where the degenerates throw DARK chocolate at you.

Hi Tim, On 03/31/2018 04:41 PM, Tim Shoppa wrote: > I would like sub-millisecond timestamps for a mono audio radio signal that > I have in the shack. > > The timestamps could be continuous (Every sample) or just every "frame" > where maybe a frame is a second to a minute. > > I would like to calibrate both the absolute time as well as the delta time > between samples based on the timestamps. (I would expect that say a nominal > 48kHz sample rate would be off by many tens of ppm because of crystal > tolerances.). > > I have a both Windows and Linux based PCs running Audacity with a local > GPS-based LAN refclock and ntpd. I trust the ntpd time to be stable to the > sub-millisecond. > > Can Audacity do this kind of timestamping for me based on the system clock? > > Or should I, say, take the PPS from a GPS, and feed it into channel 2, with > the audio going into channel 1, and make a stereo recording? I suppose I > could then manually label the filename with the second the recording was > begun. There would likely be some delta (maybe half the sample interval?) > between the two channels but I'm fine with that as long as it is at the > sub-millisecond level. Have a IRIG-B signal recorded on the second track. IRIG-B has been decoded before, here is one I threw together: https://github.com/sa0mad/irigb You can readout the time for each sample. Cheers, Magnus