AcqKnowledge software includes a Media feature that allows you to record and link participant video with physiological data. A common issue that crops up when analyzing physiological data with linked participant video is a lack of synchronization between the resulting video playback and onscreen data. This most often occurs when a USB webcam-type video camera is used. These types of cameras typically support a 30 frame-per-second rate whereas AcqKnowledge and the MP System can sample at rates up to 200,000 Hz. These factors can introduce an unwanted delay or misalignment between the video playback and data in the resulting AcqKnowledge graph.
So how do we synchronize these disparate signals to dovetail perfectly before recording our data and video? Fortunately, AcqKnowledge provides adjustment tools for addressing this common issue. This simple procedure requires the use of the AcqKnowledge software’s powerful Stimulator feature and a BIOPAC OUT103 LED Video Sync Cable.
Here is the sync method in a nutshell: With the OUT103 LED connected to the Analog Output of the MP160 unit’s HLT100C module, the AcqKnowledge software’s Stimulator is used to output a 5-volt square wave pulse into an AcqKnowledge graph, Using this setup, the LED illuminates when the 5-volt pulse is applied. The trick now is to use the AcqKnowledge Media feature and webcam to record a short video of the LED illuminating while the 5-volt pulse is being applied.
In the resulting graph, it’s easy to see in the Media playback screen when the light comes on by slowly advancing the AcqKnowledge software’s I-beam cursor through the graph data. Does the LED in the recorded video illuminate before the cursor reaches the 5-volt pulse? After? Or at the same time? Chances are, the recorded light will pop on slightly before or after the cursor reaches the pulse.
To compensate for this, the AcqKnowledge Delta-T measurement is used to determine the time interval between the pulse and when the recorded LED illuminates. For example, if the recorded LED lights up an indicated 185 ms before the onset of the pulse, then this discrepancy can be removed by setting a delay of 185 ms in the Media setup tools. If the LED lights up after the pulse onset, a negative delay must be set (ex. -185 ms). Once the playback delay is eradicated, the experiment can continue with confidence that all video and physiological data will be properly aligned.
It’s features such as this that enhance the usability AcqKnowledge Media feature, making it a powerful tool for recording and synchronizing participant video and audio during experiments. After a bit of practice, dialing in the playback video for linked Media acquisitions becomes second nature.
To see AcqKnowledge Media Synchronization in action, we invite you to view a free on-demand webinar covering this procedure in detail.
BIOPAC offers a wide array of wired and wireless equipment that can be used in your research. To find more information on solutions for recording and analyzing signals such as ECG, heart rate, respiration and more using any platforms mentioned in this blog post, you can visit the individual application pages on the BIOPAC website.