Here some snapshots of either of them:

KGuitune

QtGuitune

GtkGuitune

Description:

Guitune is a linux program for tuning guitars and other instruments by using the method of Schmitt-triggering, i.e. counting the number of triggerings between two trigger levels in a certain amount of time. Why not use FFT like many other tuning devices? Well because other tuning devices are not as fast as mine !!

With FFT you need many samples to archieve the accuracy needed for tuning instruments. You often get times of around 1 second between two measurements and the computer is quite busy in this second calculating the FFT. Using Schmitt-triggering you get a measurement every 10th of a second or even less (depending on the sample frequency you use). Most of the time the computer only waits for the samples.

The Trigger levels are adjustable. For a pure sine-wave the trigger levels could be zero. But for a wave wth overtones like the one in the figure above you need a non-zero triggerlevel. It is preadjusted to a level of 60% of the current maximum which should be able to deal with most instruments.