# FFT Spectra

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Among other things, it can be used to verify whether you are able to sing and whistle in tune or to tune your guitar.

**Examples:**

Didgeridoo

Didgeridoo is actually the reason, why i started writing this software. The theory of physics explains that when you blow into a cylindrical tube (such as didgeridoo, but PVC pipe works as well) and vibrate your lips, standing waves develop inside the tube.

At that end of the tube, where the air leaves, there is nearly atmospheric pressure and the standing wave has a node there. At the other end, where one blows the air in, the changes in pressure are maximal and the standing wave must have an antinode here.

The situation is depicted on the picture on the right: The horizontal axis represents a position along the tube and the vertical axis represents a maximal pressure variation from the constant atmospheric pressure. The black vertical line represents a zero variation. The left black point is the mouth-side enpoint of the tube. The pressure variation are maximal here. The black point on the right is the open side od the tube - the pressure is constant here.

This node/antinode restriction permits only standing waves with appropriate wavelength (e.g. frequency) to be developed. Other frequencies are forbidden. So, the red curve is a minimal (fundamental) frequency, which is present in the didgeridoo sound. (Corresponds to 70Hz on the picture bellow).

If we squeezed the red curve twice, i.e. made the frequency twice as high, on both end-points there would be an antinode and the node/antinode constrain would not be fulfilled. Really, we see that the peak at 140Hz bellow almost disappears. If we squeeze the curve a little bit more to obtain the green curve, the boundary condition is again met and the peak at 210Hz is clearly visible bellow. And so on.

**Requirements:**

· GTK+ version 2.2.x

**What's New**in This Release:

· New display mode added - waves.

· Many minor bugfixes and improvements.

Last updated on

**August 16th, 2006**