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Kami's pop quiz

🔗Jim Flannery <newgrange@...>

2/27/1996 10:20:24 PM
kami@login.net wrote:

> What is the minimum frequency that a human can perceive as a sound?
> (20 Hz, 15 Hz, 10Hz?? Give me the lowest world record.)

The question is perhaps better approached by rewording it: "...can
perceive as a _pitch_?"

Remember that when we talk about "frequency" and "Hz" we are talking
about the number of modulations from 0 air pressure to +/- n air
pressure (amplitude) per second. You can _hear_ a 1 Hz tone; it is a
transient followed, 1000 milliseconds later, by another transient (tap
.. tap ... tap).

As you increase the frequency, you first hear these transients closer
together (um, more "frequently" -- amazing language, ain't it?) until
they start to sound more like a buzzing noise and, finally, a low hum (a
pitch!) at around 20 Hz.

(I'm feeling really nostalgic remembering Bob Snyder demonstrating this
to my first composition class, sticking a couple of cables into the e-Mu
synth on the wall of the classroom and cranking the frequency up & down
in the "threshold" zone. Everything I'm recycling here is derived from
his course text (of course I never throw _anything_ away)).

This happens because our brain processes sensory data in "frames"
approx. 30-50 ms long ... so discrete events which occur more frequently
than 20x per second seem to happen continuously (we cannot perceive
their absences between them). This is _exactly_ the same process by
which we see film -- a collection of still images -- as a seamless
moving image. The threshold below which we can detect flicker in a movie
projector is approx. 16-18 frames per second (i.e., 16-18 Hz.). (16 and
35mm cinema runs at 18 or 24 fps, (sound always at 24); but many super-8
cameras and projectors run at 16 fps, a speed at which many people can
see flicker; at progressively slower speeds, more and more people can
resolve a succession of still images.)

(unfortunately, I can't find the _reader_ from that class, so I'm
dependent on the familiarity of names in the bibliography in the text
for suggestions ... you might try Lachman, Lachman & Butterfield,
"Characteristics of the Short-Term Store" in _Cognitive Psychology and
Information Processing_ (1979) (sorry, no editor listed here), Ernst
Poppel, _Mindworks--Time and Conscious Experience_ 1988), um, I'd be
guessing beyond that ... actually, I'm guessing *period* as to which
article had which data, so *definitely* don't quote *me* (e-mail me a
fax # & I'll send you the whole biblio))

Hope some of this helps...

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/ Jim Flannery / newgrange@sfo.com
/ Newgrange Media
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