https://www.nicolastiteux.com/en/blog/everything-you-need-to-know-about-pitch-shifting/

Pitch shifter pedals enable real-time alteration of a guitar’s musical pitch, offering effects ranging from subtle harmonies to extreme, synth-like tones. Modern polyphonic pedals track full chords accurately, and placing them early in the signal chain ensures the cleanest tracking and best performance. For a comprehensive introduction, visit the full article at Boss.