When used to address someone who is very
angry, this phrase generally means "calm down" or "
stop screeching" or "stop yelling." It notes that a person raises her voice in both
tone and volume when she gets upset.
Sister: I can't believe you read my diary!
Brother: Whoa... Take it down an octave. It's not like I made copies of it for everyone at
school. I only made copies for my
friends!