We know that lower frequencies vibrate at longer wavelengths and that higher frequencies vibrate in shorter, faster waves. But when you watch a guitar or bass play, you really can’t tell.
There are two different ways to see what’s going on. This upright bass was shot with a high-speed camera and played back at a normal rate, which allows you to see the strings vibrate. They look like spaghetti.
The other way to see the effect is to backlight the strings. This guy put an iPhone 4 into the soundhole of his acoustic and filmed. I’m guessing it was mounted on something to minimize the vibrations of the guitar, and the relatively cheaper camera introduces some artifacts. But you can actually see the waveforms. Notice how the bass strings at the top have longer, slower waves, while the treble strings at the bottom have more peaks at closer intervals.