Is there a word or term for when someone's voice changes in a certain way when they're nervous?

I can't quite pinpoint it. I think about all the people I've talked to over the years and can't remember any examples. The only thing I can remember is when I was on the phone with a telemarketer. My sister and I were in the background, laughing. She got up to talk to the guy on the phone, and her voice went up an octave and she started talking very slowly and like she was singing. I could not stop laughing and I asked her to stop. She said that was how she sounded on the phone when she was nervous and she thought it was funny. She told the guy and he hung up. We laughed so hard we cried.