Additionally, the code may need adjustments for some “alternative” Arduino boards…most likely the analog channel number, which may be mapped to different pin numbers on different boards.
Finally, because ADC registers are accessed directly, specific interrupts are used, and the FFT code is in AVR assembly language, this software will not run on upscale boards like the ESP32, Pico RP2040 or Teensy 3.0. It is strictly for “classic” Arduinos.