[LAD] Attenuation of sounds in 3D space

[Gene Heskett]

On Thursday, July 29, 2010 08:52:04 am Jörn Nettingsmeier did opine:

> john,
> 
> On 07/29/2010 02:35 PM, JohnLM wrote:
> > On 2010.07.28. 22:06, fons at kokkinizita.net wrote:
> >> Compared to conventional 5.1 pairwise panning the result will be
> >> more even, without emphasising the speaker locations as would be
> >> the case otherwise. In other words, the sound will be much less
> >> seem to originate in the speakers.
> > 
> > I stumbled on your own AMB-Plugins. :)
> > They seem to do pretty much what I need. Mono->B-Format panner
> > provides only angle controls.
> 
> yes. panning is only concerned with angle of incidence, whether in
> ambisonics, VBAP, or pair-wise stereo.
> 
> > 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.

Someone else was trying to describe the distance vs square law change in 
the apparent volumes.  So let me try from the broadcast engineering field to 
explain that better.   Imagine a point src of energy, be it light, sound, 
or other radiation such as a radio or tv signal.  Measured at distance x, 
you will get your reference signal, call it 0 db in this case.  Now, 
without changing anything else move your measuring instrument to a point 
that is now at a distance of 2x.  You don't get half the signal, but 1/4 of 
it, because the same energy that was hitting a square of any arbitrary 
measurement, say a square inch, has in addition to being spread twice as 
wide at distance 2x, it is also twice as high.  So the new reading will be 
-6 db compared to the original '0' db.

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 failed to find anything discussing mixing in AMB. Can I just sum the
> > channels of all sounds, like I would do it to any
> > "direct-speaker-to-channel" formats?
> 
> yes. that's a fundamental property of all linear systems, and
> independent of the signal representation.
> 
> i've written a little howto for ambi mixing in ardour a while ago, maybe
> you'll find it useful:
> http://cec.concordia.ca/econtact/11_3/nettingsmeier_ambisonics.html
> for lac2010, i tried to find out how ambisonic mixing can be applied to
> a pop production:
> http://stackingdwarves.net/public_stuff/linux_audio/lac2010/Field%20Repo
> rt-A_Pop_production_in_Ambisonics.pdf
> 
> best,
> 
> jörn
> 
> _______________________________________________
> Linux-audio-dev mailing list
> Linux-audio-dev at lists.linuxaudio.org
> http://lists.linuxaudio.org/listinfo/linux-audio-dev


-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
I call them as I see them.  If I can't see them, I make them up.
		-- Biff Barf