Originally Posted by
helispotter
... Using a 5 Hz sine wave is below my hearing range these days!
...
If a pitch link gave way and one blade was at a crazy angle of attack, then I think audio might pick up a 1 per rev (6.6 Hz) underlying frequency component. ...
No human ear can hear 5 - 6 Hz. The lower limit is 20 Hz when young, higher in adults. Therefore, all audio equipment heavily filters out lower freqs. Below 20 Hz signal strength is 0 in any audio recording.