Mr. Dude: Something is not working right for me. I am using stereo headphones (Shure SRH840). I'm playing the vid through a Dell Inspiron 15 laptop. At 0:35 of this vid there is a 200 Hz tone in the left channel. As expected, I can hear it in the left channel and not the right channel (the right channel is silent). But when you add the 205 Hz signal to the right channel, I can hear the warbling in both the left and right channel independently. When I perform the check you recommend at 1:00, I hear a warble, not a pure tone, in both channels. Is this an error in your YouTube vid recording, or is there an error somewhere else?
Most likely your laptop has some kind of audio enhancer, virtual surround, or other filter active. Turn it off and check the video again. :)
Lance Kaz