The described device is exactly such a Spectral Analyzer that is made with the help of an Arduino microcontroller. Аs you can see the device is very simple and contains only a few components :

  - Arduino nano
  - LCD display with a resolution of 128 by 64 pixels (ST7920 128x64 LCD)
  - Two resistors (10KOhm) 
  - potentiometer (10KOhm) and
  - capacitor (1 microF)

  The audio input to the Arduino is on A0, with bias at the mid point by 10K to Ground and 10K to +5V. At the input we can also set a potentiometer to control the amplitude of the input signal.
   Code is also simple and it uses "fix_fft" libray which was created for this purpose
  The video describes several cases where different types of signals have been analyzed:
  When analyzing a sinusoidal input signal, the carrier is clearly visible and By changing the frequency of the signal generator, the position of the carrier also changes.
  If we bring a rectangular signal to the input , on the spectral analyzer is clearly visible the fundamental signal, as well as the three odd harmonics x3, x5 & x7.
  If we bring an audio music signal to the input, this device is actually a graphics audio analyzer that can be found in more expensive audio equipments
  Finally, the entire assembly is housed in a suitable box. This is not a professional tool because it has low resolution and frequency range, but can serve as a great educational tool.