If you are ever in a recording studio listening to the individual microphones of each singer, you would be stunned at how off tune they can be....even in a professional environment with rehersals and vocal tuneups before hand. I had the opportunity to see one such recording session and it was eye opening. One lady couldn't hold a tune in a bucket, yet the guy at the audio board understood the problem and had the ability to tone down her vocals so it would not affect the entire groups sound. Even very talented individuals have bad days, but for the most part even top singers are mediocer eighty percent of the time. Some, never seem to have a bad day, Luciano Pavarotti was one of the greatest singers, but he was very rare and actually took care of his voice. A lot of the quality in a singers voice is predicated on how well the sound engineer is mixing the vocals during a live performance. That one engineer can make or break a performance. Maybe that is what happend to Katy during this show.