I've tried searching on the internet for this question but the answers I've got wasn't really what I was looking for. I want to know how to do a kind of "screech" on a guitar. I think it has something to do with distortion but I don't really know. I know that Angus Young(AC/DC lead guitarist) does it quite a bit, examples of songs he does it in is Live Wire and the intro to Shoot to thrill. The best example I can find is when AC/DC did Sin City live (). The kind of "screech I was talking about happens at 4:44 in the video. If someone could let me know how to do that, I'd be grateful. Thank you
This is feedback - caused when the sound energy from the amplifier causes the strings to vibrate, which is picked up by the pickups, and so on, in a cycle. It usually only occurs noticeably when the amplifier is applying a lot of gain to your signal - but this would include the use of distortion effects in the signal path, so a loud, distorting amp (or a loud amp and a distortion pedal) is the most usual recipe.
You also need to be letting the strings ring - i.e. not muting them or repeatedly re-fretting them to play other notes - which is why it's common to hear this at the end of songs, when the guitarist plays the final chord.
As the strings ring, the sound evolves as it feeds back. The timbre can evolve in a different way to a chord being sounded without feedback, because the frequency response of the feedback loop accentuates different frequencies.