While flipping through channels last night I caught some of Guns'n'Roses live at O2 concert on Palladia last night. Something weird was going on with Axl's vocals watching him. I knew he was lip-synching on at least some of the songs, but there was some other vocal audio that sounded like him in a different register going as well. I've read here that other classic rockers like ZZ Top are using "prerecorded vocals" as well these days. When these big guys are lip-synching live concerts do they also sing along live with the tracks? Obviously their mics are hot between songs for banter. Do they ever also just play entire "pre-recorded" musical performances as well? I don't mean acts like U2 that have long used prerecorded parts. Watching GnR do Knocking On Heaven's Door last night and seeing Izzy Stradlin's facial expressions and watching guy's hands made me think the whole damn song was a track playing. Otherwise it seems like there's too much chance for disaster.