Secret Base Design has
released Spectral Eye, an iOS App
to perform an FFT on incoming audio. The spectrum is
wrapped in a spiral, so that pitches that are an
octave apart are lined up as rays radiating from the
center of the display. This makes it easier to see
the notes present, as well as harmonic overtones.
The app is free, and does not have
ads. It was a tool used in the development of a few
other apps and, as it seemed like a handy utility,
Secret Base Design cleaned it up a bit and made it
available to anyone who might want to play with it.