For using fft with external ngspice, there is an (KiCad 6) example at Simulation examples for KiCad/Eeschema/ngspice - #4 by holger, project “Using the 555, a police “Dee-Dah” Siren”.
For using fft with external ngspice, there is an (KiCad 6) example at Simulation examples for KiCad/Eeschema/ngspice - #4 by holger, project “Using the 555, a police “Dee-Dah” Siren”.