While it is true that RackAFX DLLs will natively run as 32-bit VST2 or VST3 plugins, RackAFX does not use the VST API as its underlying framework. It has its own (way simpler) API. Therefore, RackAFX can not open VST plugins, so you can't use the Analyzer or impulse-response-to-frequency-response testing stuff - that only works on RackAFX plugins.

When we do native VST3 and AU plugins in my Synth Class at the University of Miami, the student use this plugin as an oscilloscope:

http://bram.smartelectronix.co.....cope_docs/

But, we have not run across a free Spectrum Analyzer. And the way that RackAFX does the impulse response testing (Frequency, Phase, Step, Impulse), where you move a slider and the plot automatically updates with a new IR test, is unique - I have not seen any software that can do this.

Another option is Adobe Audition, which can load plugins and also has some very good signal analysis features.

All the best,

Will

PS: the way RackAFX DLLs can be used as VST2/3 plugins is done via a static library that your plug-in links to called Sock2VST3; the resulting DLL has only one entrance point, DLLMain( )