source file: mills2.txt Date: Tue, 27 Feb 1996 22:20:24 -0800 Subject: Re: Kami's pop quiz From: Jim Flannery 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... -- -- -- -- -- -- -- / -- -- -- -- -- -- / -- -- ---- -- -- -- -- / / / / / / I am not fond enough of lies to talk about truth / Aragon, 1926/ / / / / Jim Flannery / newgrange@sfo.com / Newgrange Media /-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- / -- -- / -- / Received: from eartha.mills.edu [144.91.3.20] by vbv40.ezh.nl with SMTP-OpenVMS via TCP/IP; Wed, 28 Feb 1996 13:39 +0100 Received: from by eartha.mills.edu via SMTP (940816.SGI.8.6.9/930416.SGI) for id EAA12498; Wed, 28 Feb 1996 04:39:20 -0800 Date: Wed, 28 Feb 1996 04:39:20 -0800 Message-Id: <0099E96A741CE6B6.C63C@ezh.nl> Errors-To: madole@ella.mills.edu Reply-To: tuning@eartha.mills.edu Originator: tuning@eartha.mills.edu Sender: tuning@eartha.mills.edu