I'll extend my response by one word, +phase.
ILD or level difference due to phase is responsible, same applies for a pair of
coincident omni mics R=<10mm, which are shuffled to recover the low frequency
content.
See also Robins entry.
Elevation cues I find the most interesting if a structure is made to enable
elevation cues without using an ear. I recall a paper on the AES a few years
ago where blocks were used in an attempt to simulate this, not sure what became
of it.
-M
--- In "mipartitus" <> wrote:
>
> --- In "Mike Rooke" <yg@> wrote:
> >
> > > Now someone tell me how you can hear the direction of a 200Hz sound,
> > > with wavelength 1.7met, with your ears at 170mm apart, and you will
> > > know how our own ears hear stereo. :-)
> >
> > ILD
>
> Mike, at such a low frequency of 200 Hz interaural level difference (ILD),
> will not contribute much to space perception. Low frequencies (i.e. a wave
> length that is long compared to the size of the head) simply bend around the
> head (diffraction), and no 'sound shadow' is cast. At high frequencies though
> a sound shadow is cast by the head, which is detected and used for space
> perception. Roughly, ILD is negligible below 500 Hz but it may be up to 20 dB
> for high frequencies.
>
> At lower frequencies, the interaural time differences (ITD) play a prominent
> role in space perception. The ITD for a sound coming from one side (90 deg
> azimuth) is about 690 microseconds, which corresponds to 13.8% of a complete
> wave cycle at 200 Hz. This phase difference is detected and used to determine
> the angle of the sound. For high frequencies, say 10 kHz, there are many
> cycles of phase difference between the ears so the phase difference cannot be
> unambiguously related to a time difference, and ITD is not used for space
> perception (at least not in the case of pure tones). This ambiguity starts at
> around 750 Hz for pure tones.
>
> Thus, the 'duplex theory' of sound localization states that ITD is used for
> low frequencies and IID is used for high frequencies. There is much more to
> space perception than this, but, fundamentally, ITD and IID together play an
> important role.
>
> Best, Gabriel
>
"While a picture is worth a thousand words, a
sound is worth a thousand pictures." R. Murray Schafer via Bernie Krause.
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