“I had no idea how he was getting his guitar to sound like that”: Joe Walsh called him one of most underrated guitarists of the '70s and Hendrix said he was a better guitar player than he was – yet this Telecaster icon often remains overlooked

Terry Kath performs onstage with Chicago.

An electric guitar hums, then yawns, then lashes out aggressively, without abandon, in every direction.

It sounds like some free-form live Sonic Youth interlude, or Andy Gill's snarling, feedback-laden intro to Gang of Four's Anthrax. In parts – especially the moments where you can catch bits of proto-tapping – it bears a striking resemblance to Eddie Van Halen's Eruption, more in structure than in particulars.