Monitor your sound

[TubaBob]

I was giving a lesson yesterday and while I was playing my student started laughing. She said that she just couldn't stop watching the monitor on my desk (apple something.)

I stood up and leaned towards the monitor while playing and each time I played Bb below middle c, the monitor went crazy with two parallel lines vibrating near the center of the screen. It was pretty funny.

Is it just me? Is it just apple monitors?

[windshieldbug]

Happens to both myself and my stand-mate whenever we play in a certain band room. It ONLY happens when you're the one playing, not when anyone else is.

The effect changes with the note, and looks something like the weird effect you get watching a TV shot of moving wheels.

I also believe that it's just CRTs in general.

The resonance seems to vary slightly from person-to-person (and/or horn-to-horn, but to be honest, it didn't seem important enough to warrant any further study... )

[Rick F]

What I think you're seeing is a beat frequency between the refresh rate of the monitor and the vibration of the note you're playing being felt in your eyes. Similar to what you see if you use a vibrator at the back of your neck while watching TV.

The moving television picture (or CRT monitor) is actually a series of still pictures. In the USA there are 30 complete pictures per second (60 frames/second / 2 interlaces per frame). This rate is not much higher than the flicker fusion rate of the human eye. If you look through a rotating fan at the TV screen, and you will see lots of jumping around. It's like a strobe effect.

[GC]

When you play, the motion of your lips sends vibrations through your head, though it's less than the strength of the pressure waves in the air. When these waves reach the eye, they cause the retina to move with the vibrations. The motion is extremely small, but so are the visual receptors in the retina. The motion of the receptors is enough to cause interference effects with the player's viewing of TV and computer monitor scan lines.

TV has a 30-picture/second scan rate. Computer monitors have variable screen refresh rates, although most users are not aware of them. Most are set to 60 by default. Slow refresh rates cause some viewers to feel like the screen is flickering, especially if the room is lit with fluorescents. Changing to a higher scan rate usually gets rid of the flicker (75 or higher works for me). However, changing to extremely high rates doesn't help further and can actually degrade the performance of the computer.

With different refresh rates, the notes that you play on tuba to get the most pronounced visual effects will change. Higher rates will take slightly higher pitches.

[Tuba-G Bass]

Hi tubenetters,

Since I work in TV, I'll weigh in here,
Rick F wrote "In the USA there are 30 complete pictures per second (60 frames/second / 2 interlaces per frame)"

He had it very close, but there are some slight frequency
adjustments made to keep 60Hz AC power from causing a hum
bar on TV's, so real numbers are 59.94 fields/29.97 frames per
second for our TV standard NTSC, a field is all odd or even lines.
When I visited England in 2005,
Their standard PAL sometimes had a flicker to it,
since theirs is based on Europeon 50HZ AC power,
so they have 50 fields/25frames per second.

I have heard of a similar effect, a TV editor was watching a
show he had just put the finishing touches on, He eat his lunch which included potato chips,
he saw a "drop out" in the show, which is a bad frame caused by several posible causes.
He rewound the tape, watch it again,
nothing! perfect video!
He finally realized that eating the chips caused
his eyes to "see"
breakout in the picture, same would go for
Celery, Carrots, and other "Crunchy foods".

Some Computer screens use higher refresh rates,
75hz in common, and now the more common LCD's
are usually using 60 hz refresh rates, plus they all are progressive frames,
with all the even/odd lines drawn together.

HDTV is now getting to be more popular,
they have both interlaced and progressive frames,
signified by the i or p after the scan line count,
good ol' american TV is 480i,
then some of the newer types of content come in 720p & 1080i, and even 1080p and 480p.
Let's not forget that there is aspect ratio variations too,
vanilla TV is 4:3, then there is 16:9, the wide frame format,
its getting to be very complicated, whew!
Like having Tubas in different Keys and tuning standards all running around. oh wait!
Hmmmm

[eupher61]

great explanation, Paul!! (And, it's correct, too, which makes it even better!!)

[Norm in Bellevue]

Very interesting thread! Just a few weeks ago when the weather was quite warm here, I was playing descending scales while gazing out the window toward my neighbor's upstairs window. There was a box fan running in the window. When I got down to some really low note, my eyes seemed to have "stopped" the fan blades. I knew it was the vibration in my head and eyes, but thanks for the technical explanation. I thought I was the only tubist on earth who had experienced this phenomenon.

[GC]

TFT LCD screens don't flicker like CRT screens. As long as voltage is applied, the picture stays up and doesn't have to be redrawn, so even a 60 Hz refresh rate won't cause flicker. Only changed pixels are affected by the refresh, and their lag in change rate keeps a flicker from being visible.

[windshieldbug]

And all this time I thought I was losing my mind over certain notes

Oh, you are... all this is purely coincidental!