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.
If the above links won't work you can also try this mirror
or download the latest version from sunsite at
ftp://www.ibiblio.org/pub/Linux/apps/sound/ and ftp://www.ibiblio.org/pub/Linux/X11/kde-apps/sound/
also check out my Linux-Page
for more free linux software.
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Florian Berger - email@example.com