Physical audio visualizer





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Published on May 15, 2010

Everyone has seen the colorful, morphing visualizers on music players, but this one involves no code at all. Just a speaker, tape, a reflective surface, and a laser.

I opened up my digital piano and taped a piece of polished silicon wafer on the back of the speaker cone. I then aimed a laser (a blue one then a green one) at it, put a camera on the floor aimed at the reflection, and played different intervals on the piano. When the laser is still, you may notice a slight flare on a diagonal; that is because the silicon structure has a grain to it and slightly diffracts the light.

What I find most interesting is how directly the pattern correlates to the nodes of interference from different intervals. The harmonic resonance from the 4th and 5th intervals make a much more uniform pattern, whereas a minor second makes the laser pulse, just like the beats you hear. Intervals like major sevenths and tritones make a crazy interference pattern, too. Also, purer tones make purer circles. It is interesting that the lower notes include natural impurities that make the shape not circular.

The camera really doesn't do it justice because it doesn't focus well on a single bright dot in the dark, and the frame rate sometimes clips some of the motion. But it is still pretty fascinating on several nerdy levels! Playing a song just made a bunch of noisy patterns, not as neat as one note or interval at a time. Playing chords of more than two notes just made a messier pattern too.

Thanks for the idea, Dad!


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