I wasn't there for Cheap Trick's Sunday night set at the Voodoo Experience, but the consensus among several people who did go was that CT performed a real cheap trick and lip-synched through most (if not all) of their set.
On the disappointing side, Cheap Trick was scheduled to play the Bingo! Parlor stage, the notion being that the show would be a more intimate affair. The band sounded exactly like it does on its albums — because it appeared to lip-sync the entire set.
[Robin] Zander’s voice, which couldn’t really be expected to stay in its pristine register after 40 years, got help. There were a couple of awkward moments when he didn’t quite sync up with the vocal track that was laying a comfortable foundation for his live efforts. One local musician was upset. “It’s undignified,” he said, before skipping out to catch the Meters.
Based on the YouTube captures from the show — well, the vocals sound awfully good, pitched in an arena register that doesn't quite match the small Bingo! stage at Voodoo:
"I Want You to Want Me":
Were you there? What did you think?