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jbasch
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Join Date: Dec 2010
jbasch is on a distinguished road Posts: 4
Hi. I have compared the Stimtracker audio marker to the Biopac HLT100c marker on a MP150 system in AcqKnowledge 4.0 and have found a consistent 1 ms delay from between the two (with the HLT occurring first). See the first picture. Iím unsure which is more accurate. Any thoughts?

I also tried using a DC square wave created per Biopacís AS-214 document on the right channel with the audio signal on the left going directly to the Stimtracker and I find the signal onsets having a discrepancy of 18ms. See second picture. Iím unsure which digital channel the Stimtracker is sending the left and right signal to so I donít know which signal is delayed. Any thoughts on what might be causing this?
Iíve included the audio file.

Thanks!
-Joe
Attached Images
File Type: png stimtracker audio markers compared to biopac hlt100c.PNG (135.8 KB, 2 views)
File Type: png stimtracker audio markers.PNG (121.1 KB, 2 views)
Attached Files
File Type: wav startle with marker.wav (11.3 KB, 2 views)
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Hisham
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Join Date: Aug 2006
Location: San Pedro, CA
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Posted September 12th, 2018 #2
A colleague tested the audio file that you posted. m-pod pin goes high 500Ķs after the start of the sound with the default threshold setting of 50. If you reduce the threshold setting to 10, the delay from the start of the audio to m-pod output is reduced to <100Ķs.

The 18ms is the length of the DC pulse being fed into the audio input. The audio input is meant for AC signals so it only sees transitions of a DC signal. Because StimTracker is looking for the envelope of the audio, it sees the falling edge of the input pulse.

If you want to use an audio channel as a marker, I suggest using a tone (e.g. 1kHz) rather than a DC pulse. If you wish to use a DC pulse, you can try feeding it into one of the light sensor inputs.
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jbasch
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Join Date: Dec 2010
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Posted September 13th, 2018 #3
Thanks! This is helpful.
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