At last version 5.0 is
here!
(wait for a while till it gets approved)
A lot has been done, thanks to the help from TF3RDL, sveakul, boroda and Steven!
The new version supports 3 sample sources:

The RAW API is the new one, freshly developed by Steven for MB3.6. Earlier versions have to use DSP or the native FFT.
For the DSP you'll need the dsp_nostalgia.dll

To use the RAW API - mb_nostalgia.dll

Both are c++ plugins which pick and transform the audio samples.
Among the new things are:-Mid/Side channels option- makes sense only for DSP or RAW API sources!
-More flexible and resizable/expandable Note Scale
-Support for cubic spline interpolation
-Automatic generation of skin-colored vizualization
-Different Fourier transformation sizes - 2,4,8K
On how to setup the RAW API:-Use MusicBee 3.6.9041 or newer (the latest patch).
-Use the latest MusicBeeBass.dll from Steven.MusicBee 3.6.9042 has already the MusicBeeBass.dll into the zip package:
https://getmusicbee.com/patches/MusicBee36_Patched.zipAny suggestions, ideas and bug reports are welcome.