After being inspired by 6.163, MIT's famous "Strobe Lab", I decided to come into the lab and do some high-speed video work to capture something very dear to me, musical instruments. I began by filming a cymbal crash. My goal here was to capture the sound of the crash and compare the video to a Fourier Transform of the audio to see if some of the fundamental frequencies were visible as physical modes. I found that there was a fundamental frequency at around 3kHz and so I experimented with adjusting the frame rate to see if I could effectively alias down this mode so that it would appear to be still. I also sampled above the Nyquist rate to prevent any aliasing of this primary mode. Here are my results:
I had some extra time so I had my friend Richard play some guitar notes for the Phantom high-speed video camera. Here are the results. The first two videos show a single note being plucked, the first right after the pluck and the second several seconds later. The results are pretty wild.
I then had Richard play a few harmonics to see how visible the physical nodes were. The first video below shows the first harmonic, sounding an octave above the fundamental. He divides the string in half with his finger lightly pressing against the string, forcing it into a mode with a single center node. The second video has him doing the fourth harmonic, dividing the string into 5 equal parts by forcing the string into a mode with 4 nodes. They are a bit difficult to see, but they are definitely there.
Finally, I just thought it would be cool to see a bunch of strings playing the same note in different octaves simultaneously to see how their frequencies are just integer multiples of one another.
I ended up preparing a presentation for the professor, Dr. Bales, formalizing my results. The Fourier Transforms of the cymbal crashes are shown here as well.