[Arny Krueger[_4_]]

"PStamler" wrote in message
...
On Mar 6, 4:36 pm, "Arny Krueger" wrote:
"PStamler" wrote in message

...

William mentioned that few microphones have significant response over
20kHz. I've looked at some of my students' recordings using a spectrum
analyzer, and there was plenty of 20kHz+ signal present. I don't know
exactly which mics were used on which recordings -- most probably
various Neumanns on most of them -- but there was lots of signal up
above the audible range.

What exactly does "plenty of 20 KHz+" mean in dB @ various frequencies?

I don't have quantitative figures, merely noted that as levels on the
spectrum analyzer rose and fell with the music, there was significant
content 20kHz. In some instances, greater than between 10-20kHz
(possibly due to microphone resonances in the ultrasonic regions).

Then there is the problem of the human ear's construction.

(1) Note that the Fletcher Munson curves fall off at approx 12 dB/octave
above 5 KHz. That's for a normal young adult.

(2) Hearing is based on hair cells within the Organ of Corti on the
Basilar
membrane, with the high frequency related hairs first. The first cells
generally respond to frequencies just below 20 KHz, and there are no hair
cells that respond to higher frequencies.

(3) Masking. If the spectral content of the sound being heard is not
rising
at a rate of 12 dB/octave then lower frequencies will control the
critical
band and the higher frequencies, even if audible by themselves, will be
masked and not heard.

What's that got to do with whether microphones produce significant
output over 20kHz?

It means that few if anyy ever actually hear it. Therefore, it is largely
sonically moot.