I can tell the difference at 12. There's a flash test at http://jakemandell.com/adaptivepitch/ http://jakemandell.com/adaptivepitch/ and the (probably heavily s

I can tell the difference at 12. There's a flash test at http://jakemandell.com/adaptivepitch/ http://jakemandell.com/adaptivepitch/ and the (probably heavily sample-biased) histogram at the end suggests 10-20% of people can't differentiate 1/4 of a semitone and 60% ish can't differentiate 1/12.