The most amazing pitch shifting I've ever gotten is out of my Roland Guitar Synth.

https://www.roland.com/us/categories/guitar_bass/guitar_synthesizers/

Here's why...

Most pitch shifting effects apply to the guitar signal as a whole, which means all of the strings at once.

The Roland Guitar Synth / pickup splits the signal of each individual string and treats them separately. (6 different pitch shifters, so you can control each string's pitch separately). This makes a HUGE difference in the quality of the pitch shift effect.

Most importantly, chords come out sounding realistic! Rather than a weird fuzzy confused digital noise sound.

I tuned my whole guitar down an octave with it and it sounded totally realistic, no digital pitch-shifting artifacts you'd usually get when all the strings are processed together.

I'd like to do more with this tool the future. Never heard anything like it.

-Carl.