I didn’t realize you were recording audio responses. The log command on the MediaRecorder element will report when the recording started, so you’ll be able to compare that timestamp to the timestamps reported by your Audio element’s log command, and then manually measure when your participants start speaking in each of your collected recording files.
Say your Audio element starts playback at timestamp 1111 and your MediaRecorder starts recording at timestamp 1234 (the timestamps in the results files are in fact much longer, but it doesn’t matter), and by analyzing the recorded sample you find a 250ms silence before your participant starts speaking. This means that your participant gave their audio response 1234-1111+250 = 373ms after the onset of your Audio stimulus.
Let me know if you have any questions