If you're going to make a comparison, compare the same time of day. I sing a particular song with a very wide range. If I sing it in the morning, I can pitch it lower than I can in the evening. I sing in a Men's Chorus that sings at 8 in the morning, and it's touch and go whether the range is there, each time. Sometimes my throat hasn't completely cleared at that time. Sometimes my eyes aren't even completely open.

Jerry