Basilar Membrane Motion 3: Click Trains - Animation

 

And another animation showing the mechanical response of the basilar membrane, but this time the incoming sound is a 500 Hz click train i.e. one click every 2 milliseconds. Such click trains sound like a "buzz" with a very clear pitch at the click rate.

The Fourier spectrum of such a regular click train is composed of regular spaced harmonics at multiples of 500 Hz.

 

The top trace again shows the click stimulus, while the bottom trace shows the basilar membrane, with distance from the basal end on the x-axis.

This animation may help illustrate the important concept of resolved and unresolved harmonics. Note that both the 500 Hz and the 1000 Hz points of the basilar membrane respond with regular vibrations, while the region in between (around ca 700 Hz) appears to be more or less at rest. Place along the basilar membrane is therefore said to "resolve" the first two harmonics (500 and 1000 Hz) of the click train stimulus, as each produces a distinct region of high amplitude vibration, clearly separated by regions of low vibration amplitude. However, the points on the basilar membrane tuned to higher harmonics (say 2000, 2500 or 3000 Hz...) do not show distinctly separate peaks in their vibration amplitude, i.e. these higher harmonics are "not resolved".

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