The "Graphical Periodicity" of musical notes.

This is a simple illustration of the "graphical periodicity" of musical notes. I set the scan rate of the display to roughly match C1 and you will see it has a single crest. Moving up an octave to C2, there are two crests as the frequency has doubled. Up another octave there are four crests to the waveform, and so forth. Using a note that isn't a multiple of 32hz causes the waveform to "scroll" on the screen. This is an illusion caused by the same reason that a vehicle wheel appears to spin backwards at a certain speed, and can be corrected by making sure the scan rate is roughly equal to a multiple of the frequency of the sound being played. Old oscilloscopes used to use circuits similar to modern digital instrument tuners to dynamically adjust their scan rate to compensate for this.

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Science & Technology

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