a weird visual phenomenon while playing

[kontrabass]

This was inspired by the recent post from our friend whose teeth rattled when he played loud...

I've noticed for years that sometimes if I'm playing and I glance at a TV, or an LED light, or a clock radio, or computer monitor, etc. etc. those lights appear "wavy". i.e. they move back and forth at a regular rate. But not fast, more like 5 or 6 Hz.

I've assumed this is something to do with the lights' refresh rate somehow lining up with the frequency of the note I'm playing, but I don't know how it works, and it's totally trippy. Just curious if anyone else experiences this, and has a more precise scientific explanation?

[hbcrandy]

I, also, have experienced this, especially when playing in the low register. I do not have the knowledge to explain this scientifically, but it happens to me. However, I do not have the sensation when reading music on a stand. I only seem to experience it while playing and looking across the room at a television or computer screen.

[Lectron]

You shouldn't smoke that stuff

(happens to me to playing contra, bicycling in rough terrain etc...Eye muscles probably can't adjust to the vibrations)

[imperialbari]

The stroboscopic effect comes from interference between the refresh rate of the TV and the frequency you play. The latter transmits to your eyes and/or glasses, if your facial tissue is stiff from low temperatures in the environment or just from inactivity that causes a reduced blood supply.

In my case I sensed the glasses more or less dancing on my nose. The remedy is fairly simple: give your nose and the area around your eyes a good rubbing.

Klaus

[MikeW]

In rooms that are lit by fluorescent tubes, you can sometimes get the light level to seem to fluctuate slowly by humming deep chest notes (this doesn't work if you have anti-stroboscopic workshop lighting). I always assumed it must happen because the vibrations in the eyes are somehow strobing with the light. The effect seems to be more pronounced in the peripheral vision, which is more sensitive to flickering lights.

If you get a TV with an LCD screen, you can usually run it at a higher refresh rate, so both the flicker and the stroboscopic effect will go away.

[Norm in Bellevue]

Something similiar happens to me when I'm sitting at my keyboard, gazing out the window at my neighbor's box fan sitting on a window sill. When I blow certain low pitches on the mouthpiece, I can make the fanblades appear to stand still.

[Karl H.]

Not meaning to be simple, but I always thought the phenomenon was the liquid/gelatin-like viscera of my eyeballs vibrating! At low frequencies (and we're mostly dealing with low frequencies) I would be surprised for there NOT to be a 'whole lotta shakin' goin' on'. The skull has lots of open spaces (sinus) and those air columns/pockets would vibrate in sympathy with whatever pitch is established by the lips and air column: I assume the watery eyeballs would vibrate also, especially when the vibrations are slow and long.

Somebody with medical or acoustical experience could answer this for us, I bet.

Karl "I'm NOT a doctor, Jim!" H.

[tubajon]

It's def the eyeballs vibrating.

[Roger Lewis]

My skull is pitched at an A. When I play any A my vision blurs just a bit, depending on how loud I have to play it. The conductor vanished at one point during Carmina Burana. The eye balls vibrate at a slightly different frequency than the skull frequency. At least that's my theory.

Roger

[imperialbari]

It's def the eyeballs vibrating.

Certainly they do, when you experience that phenomenon. Those wearing glasses also will experience the glasses vibrating. As hinted in my first posting, it is possible to diminish the transmission of those vibrations from the lip area to the eye area.

Klaus

[Rick Denney]

My skull is rather broad-banded. It vibrates on all notes.

Whether it's the skull shaking the eyes, or the vitreous humor vibrating within the eyeball, the result is that the eyes move back and forth. (I suspect it's not the vitreous humor vibrating in sympathy--the eyeballs are small and the resonant frequency will be very high--probably more than high enough for the vitreous humor fluids to damp out. Old television screens (in the days of CRT's and NTSC) refresh at 30 frames/second, interlaced. Thus, the movement of the eye will see an aliasing or interference effect with the motion of the scan of the screen. Low A is 55 Hz, low Bb is 58 Hz, and low C is 65 Hz. The vibration on the low A will find a 5-Hz interference pattern with the 60-Hz overtone (or the 60 Hz basic refresh rate of modern HDTVs). The Bb or B might be close enough for the interference pattern to not be that visible, but the C will also produce a 5-Hz intereference pattern. These are beats just the same as you hear when you are out of tune with your neighbor in the section.

Flourescent tubes also flicker at 60 Hz, which is the frequency of the AC electricity used to power them. I'm using flourescent curly-cue bulbs in the practice room these days, but I haven't really noticed an increased vibration effect. But my vision is bad enough so that a little vibration may not escape the general blur.

Or maybe my head has become more well-damped as I've aged.

Rick "refusing further speculation" Denney