There is no such thing as "perfect" sound. That's what I argued back in April, as part of our World Voice Day "Microphone Workshop" at City Tech (my writeup of the event with photos here). My talk kicked off the day's sessions, and in it I attempted to lay out many of the challenges to getting good live sound. I targeted the singers and voice teachers in the conference's audience, but my hope is that the talk will be interesting to anyone who is a live music fan or who buys a ticket to a show, as I also proposed some basic, non-technical, objective criteria about what "good" sound is in the first place.
Unfortunately, the video of the event got corrupted, but I did get an audio recording, and today got time to cut the recording against my Powerpoint slides and a couple other photos. It's 30 minutes long, and I hope worth your time: