Revert "Merge branch 'recording'"

This reverts commit 080e7700b009a9dfb2fef641f9ba3801b6605c6b, reversing
changes made to a73769297f8a92e3631f25d01296a5f859fd2f00.
re-add AVFoundation framework
Pick a good calibration value for showing sound levels
add some notes, but the math is wrong