Page 1 of 1

Time of epochs

Posted: Tue Jan 08, 2013 10:34 am
by Chanel
Hello to the Biosemi community,

I have accidentally recorded an epoch in one of my biosemi file (certainly by pausing the actiview). The problem is that I am relying on the absolute time of the recording to synchronize my data (I know that there is a max one second lag as mentioned here: viewtopic.php?f=1&t=66&hilit=epoch+time , but I am taking care of that by sending triggers periodically). Since I paused the recording it seems I cannot know what is the absolute time after the pause (start of the new epoch). I tried to crop the file with a start time corresponding to the start of the epoch (N) but it seems that the start time of the BDF remains the same (i.e. the absolute time are wrong when using EDFbrowser since it still start at time X although the file as been cropped at X+N).

My questions:
- is there a way to know what was the absolute time of the start of a new epoch ?
- is there a way to reconstruct a BDF file with only the epoch and the right absolute time.

Thanks for your help,

Guillaume

Re: Time of epochs

Posted: Tue Jan 08, 2013 2:11 pm
by Coen
If the absolute time is not coded in the trigger codes, then there is no way to retrieve the absolute time after starting a new epoch (after a PauseOn/PauseOff sequence).

The start time in the BDF header is the moment when the Pause button was released for the first time (and the data actually started streaming to disc).

Best regards, Coen (BioSemi)