Nyquist was wrong?!
Reply #56 – 2003-07-25 19:49:15
I have never said anything about us being able to hear beyond 20kHz. I was never referring to steady state signals. <snip> I didn't say so. I'll try to clarify: I know that transients don't consist of one frequency, nevertheless they can be transformed to frequency domain (and back). Your claim was:As it has been stated in this thread, it should be impossible to hear filter ringing with fc beyond human hearing. This is INCORRECT. It might be tempting to think so. The human hearing cannot hear steady-state sines over 20kHz. If you lowpass a transient (e.g. silence with a single 1-sample click), pre- (and post-) ringing arround fc is introduced. Making the lowpass steeper causes - the ringing to become louder - the ringing to last longer - the frequency range of ringing arround fc to become wider. I've tried this with CoolEditPro. Even if silence with a single 1-sample click is lowpassed (using fft filter) at 20kHz with a lowpass width of only 6 Hz, the frequency range of ringing is between 19500 and 20500 Hz, so still out of audible range. So why should adding a 19.5-20.5 kHz increasing + decreasing sound to a signal change the signal noticably if we can't hear the added sound itself at all?... This pre-echo will get the inner hair cells into detection mode. This starts the outer hair cells depolarizing and going into compression mode (by detuning basilar vs. tectoral membranes). When the center of signal arrives (a transient) instead of the full level, the compression has reduced the sensitivity of the system, so the central impulse does not sound as loud. I understand your explanation about the ear very well as I'm studying medicine. It's clear and a known fact that it works like this if a pre-echo (or any "sound before a sound") is audible - but is there any proof that it works like this if the pre-ringing is in a conciously inaudible frequency range? Does the sound reach the inner hair cells at all - and, if yes, do they react? Any neurological measurements done on this you know of?1. We are not talking about steady state signals. Well, pre-/post-ringing is not stead state, but short "steady state with fadein and fadeout". Why should this cause a difference in perception?