Demonstration of Qt with the FFT library FFTW
Credits to Joel Svensson:
https://svenssonjoel.github.io/pages/qt-audio-fft/index.html
I got the code from here, but no working project in Qt at Joel his website.
With the file's I provide here, you should have a working example out of the box, took me some time to get everything working.
Used Qt 5.15.2 with the minGW compiler, newer version did not work, something changed in the classes used capturing the sound.
