Hi,
Date: 20 Jul 2011 11:36:10 +0100
From: dave.mal...@york.ac.uk
Hi all,
I think that one of the problems with all these discussions is
that we
tend to think of the distance of an audio object as being the
exactly the
same sort of thing as the coordinates of the object w.r.t. the
listener -
but it's not because, unlike direction, we humans can't determine it
absolutely, but only as implied via the object's (and our)
interaction with
the environment. For a unknown distant stationary source in an
anechoic
environment there are _no_ cues as to distance, unless the listener
can
move and gain something via parallax or loudness variation. For close
sources (i.e. in the curved wavefront zone) there may be some cues
from
bass lift, but even these would be ambiguous for median plane
sources if
head turning is not allowed (Greene-Lee head brace, anyone?)
Dave M.
Agreed, though you are really talking of a particular (and fairly
uncommon) situation. An unknown sound source, which implies something
electronically generated, and thus with no readily identifiable
source. An anechoic environment.
Apart from HF absorption by the air, only really appreciable at quite
large distances, the only variable is then loudness, the same sound
louder or quieter. As we have no knowledge as to how loud it is
supposed to be at a given distance, we have no reference point for
comparison.
In a 'soundscape' containing several sources some distance
relationships between them can be discerned. Of course this is aided
by prior experience. Given a recognisable sound source, such as a
blackbird or violin, amplitude alone gives some rough idea of
distance, though it cannot be stated with any accuracy. Given two
familiar sources, a rough relative distance between them can be
perceived.
Any sense of scale can be disrupted by playback levels that are
louder or quieter than 'real' levels. Loud sounds are more
'present' (nearer ?), and are usually produced by larger sources.
I, like I suspect many on this list, am interested in how aural
compositions can be made spatially 'effective': to convey convincing
and believable images, even if they are 'unrealistic'. Most modern
audio production for music, film or any other medium aims to produce
something 'hyper-real': clear, polished, stripped of extraneous
sound, crafted. The listener is usually static.
Ciao,
Dave Hunt
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