Total speculation but I would expect to use a frequency that is as much in the roundhouse of as many instruments as possible. 2 hz is not a big change though I would expect if so it was determined to be a better fit. You can look up music frequency charts online that will show you the harmonic frequency ranges of common instruments. I have one on my wall. It comes in very handy to help me understand what I am hearing when listening to the ol hifi better.
