I have seperate audiomoths set over 3 sampling periods 8-10th March 2021, 13-15th March 2021, and 19-21st March 2021. All were set to record 10:00-19:00 (UTC). On downloading my files those recorded in the first sampling period have recorded from 10am - 6:59pm while the next two sample periods have recorded 11am - 7:59pm. All config.txt files state 10:00-19:00 (UTC) and Timezone (UTC). Any idea why there are time differences??
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Yep, I've been playing around copying files and changing timezones, and it's hard to understand exactly what macOS does, but the WAV file on the SD card and the TEST.TXT file have actual file creation times of 00:47 and 00:36. However, if you change the time zone between opening the SD card and copying TEST.TXT onto the SD card, you can end up with a permanent time offset between the two - in this case one hour
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Thank you that makes sense. I looked at the 'More info' tab once on my local drive and can see despite the WAV file displaying different times the recording times are the same (phew). When Im saving the csv files when performing analysis in Kaleidoscope it is time stamping each with the WAV file times so I will just manually correct this time in my excel files.
Yes, ignore the file creation and modification dates. The FAT and exFAT formats that the SD cards use don't allow any timezone information to be stored along with the times in the file directory and these times have to be written in local time or UTC. This becomes become confusing when timezones change as I think macOS tries to be helpful and converts the times again. Use the timestamp in the file name which in your screen shot above is 10:00 UTC on 19/3/21. The same timestamp is written in the header comments within the WAV file which will appear under the 'More Info' tab. The latter doesn't always appear immediately as the macOS has to open each file and read it to determine this information. Copying the file to a local drive typically forces this to happen.
The example above was recorded at 15:20 UTC with the timezone set to UTC+1 so the timestamps in the WAV header and the file name are formatted as UTC+1 and the CONFIG.TXT file will show the recording period as starting at 15:20 UTC.