From: rcd@ico.isc.com (Dick Dunn)
Subject: Re: What is the resolution of human hearing?
Date: Thu, 18 Jul 1991 23:12:15 GMT
Organization: Interactive Systems Corporation, Boulder, CO




dnettles@libserv1.ic.sunysb.edu (David E Nettles) writes:

> What is the resolution of human hearing?
> 
> For vision I think it is 24 frames/sec.  What is it for sound?

The term "resolution" is a funny one to use in this context.  Even for
vision, 24 fr/sec isn't a measure of what we normally call "resolution."
(More correctly, we'd measure the subtended angle of the smallest object
which can be seen, in the center of vision [on fovea] at optimal viewing
distance [25 cm is a "typical" figure].)

> [MODERATOR'S NOTE:  I think that the human ear is sensitive to frequencies
> from about 60 Hz to 17KHz; the phone tops out at around 8 KHz...

The "standard" numbers for human hearing are 20 Hz to 20 KHz, which is
about 10 octaves if you want to think in musical terms.  The phone is
limited to 3 KHz.

The upper end of hearing goes down with age (much more rapidly in men) and
with repeated exposure to loud noise...for all but serious music and good
ears, you can lop off an octave and top out at 10 KHz.  Similarly, you can
often move the low end up an octave or more.  In the US, 60 Hz is power-
line frequency; if you think of the "hum" associated with, say, transfor-
mers and ballasts, that will show you it's a pretty low tone.

Sensitivity (minimum audible sound level) varies dramatically over the
frequency spectrum.  The most audible frequencies are around 1-3 KHz.

There's a ton of information available on human hearing response.  One of
the best sources, accessible to anyone with reasonable college math, is
_Acoustics_ by Leo Beranek.  It's been a [?the?] standard acoustics text
for a long time; some of the information is a bit dated but still usable.

You might also ask, in terms of "resolution", how close two sounds may be
in time for them to be perceived as having started separately.  While I
don't have the numbers for this, a place to start is by looking at the
discussions surrounding MIDI:  It needs to be able to start several sounds
"simultaneously" in order to produce a proper-sounding chord.  I have some
vague memory that MIDI has a problem there, but I don't know.

Yet another aspect of "resolution" would be the ability to localize a sound
source based on the "triangulation" we do with our binaural hearing.
Again, this is something which is very frequency-sensitive, for the obvious
reasons (e.g., a 100-Hz tone has about 3-meter wavelength, which kind of
oozes around everything).

Hope this is a start.
-- 
Dick Dunn     rcd@ico.isc.com -or- ico!rcd       Boulder, CO   (303)449-2870
   ...Simpler is better.