[LAD] Attenuation of sounds in 3D space

Fernando Lopez-Lezcano nando at ccrma.Stanford.EDU
Thu Jul 29 17:00:10 UTC 2010


On Thu, 2010-07-29 at 16:14 +0200, Ralf Mardorf wrote:
> On Thu, 2010-07-29 at 17:01 +0200, JohnLM wrote:
> > On 2010.07.29. 15:20, Gene Heskett wrote:
> > > On Thursday, July 29, 2010 08:52:04 am Jörn Nettingsmeier did opine:
> > >
> > >> john,
> > >>
> > >> On 07/29/2010 02:35 PM, JohnLM wrote:
> > >>> So from what I can understand, if I apply doppler effect, distance
> > >>> attenuation and other pre-process filters to a mono input and then
> > >>> push it through the panner plugin I get fairly correct representation
> > >>> of sound in 3D space. Right?
> > >>
> > >> depending on what you mean by "fairly correct", "representation", and
> > >> "3D space" :-D
> > >>
> > >> doppler would come into play only if you change the distance of the
> > >> sound, not when you move it on the sphere, as the distance remains
> > >> constant.
> > >
> > > This use of 'doppler' I would call incorrect, because the doppler shift is
> > > a shift in the apparent frequency of the sound rising at it approaches, and
> > > decreasing as it leaves.  I'm sure you have a term for what you mean, but
> > > doppler isn't it.  That police officers radar gun measures your speed by
> > > listening to the echo from your vehicle, and comparing it to the signal its
> > > sending, which to simplify, results in a beat frequency which is exactly
> > > your speed if approaching or departing exactly to or from the radar guns
> > > position.  That is why it is often called doppler radar&  the weather guys
> > > us it also.  Because they don't stand directly in front of you to take a
> > > reading, there is some small vector error in your favor.
> > >
> > >...
> > >
> > > That is why we call it the square law.  The only way to get that back is to
> > > make the receptor itself 4 times bigger.  But while I have observed that
> > > there are quite wide variations in ears, I have not seen an individual with
> > > expandable ears (yet) :)
> > >
> > >> when you hand-craft distance cues, you should not expect wonders for
> > >> sounds originating inside your sphere of speakers. travelling through
> > >> the center quickly can be made to work, though.
> > 
> > I am fairly sure 'doppler' *is* what I meant.
> 
> You notice a Doppler effect? So your speakers are far apart from each
> other, while you are moving very fast from one speaker to the other?
> Nothing else is called the Doppler effect.
> There might be a sound similar or equal to a Doppler effect, but of
> course using this term is bad.

You don't understand. 

The previous posters are talking about _simulating_ moving sound
sources. So you, the listener, stay in place, and the composer or sound
artist is crafting cues for you that will simulate the movement of
sources around you. If those sources move towards or away from you (ie:
have a radial component of the velocity vector) then you should simulate
the doppler effect they would have if they were real objects. It is a
very powerful cue. 

So, yes, it is doppler and no, use of the term is not bad or incorrect. 

-- Fernando

PS: for example, read:
  https://ccrma.stanford.edu/courses/220a-fall-2001/chowning.pdf
  http://www.dxarts.washington.edu/courses/567/08WIN/chowning.pdf





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