SPAN is a free real-time "fast Fourier transform" audio spectrum analyzer plug-in for professional music and audio production applications.
For the most part it was derived from Voxengo GlissEQ dynamic parametric equalizer and reproduces its spectrum analysis functionality. SPAN conforms to AudioUnit and VST plugin specifications, and is available for Mac OS X (v.10.4.11 and later) and Windows (32-bit and 64-bit) computers.
List of changes in version 2.2:
As a side note, Voxengo User Survey located at http://www.voxengo.com/usersurvey/ is still accepting your answers (you do not have to be logged in to participate).
Voxengo pro audio plug-ins can be downloaded at the Voxengo web site: http://www.voxengo.com