Seems to be a brain thing, I can play a constant sine wave low note around 42 to 100 hz and turn up the volume. If I turn up the volume about 10 db it sounds like the pitch increases almost a half step. Pretty crazy but for me it's true, take it from an old piano tuner, my sense of pitch is well trained. Got a little time? try it and listen, it might just be me, but maybe not. Never thought about lowering the pitch based on the volume. May try that someday on a reaktor project.