Re: [LAD] Attenuation of sounds in 3D space

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.
> >
> > 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 am fairly sure 'doppler' *is* what I meant. I work on spatialization
> project where sound sources can and will move around on arbitary
> trajectories in virtual space.
>
> Well as for 'distance law'. Microphone receives and registers sound
> pressure instead of sound intensity.
>
> intensity != pressure
> intensity ~ pressure^2
>
> While true that energy at 2x distance is 1/4, the pressure excerted is
> 1/2 neverheless (pressure value is independent of area - i.e. it uses
> constant nominal area).
> So you end up with a linear correlation instead of square one.
>
> pressure ~ 1/distance
> intensity ~ 1/distance^2
>
> There is also the thing with acoustic impendance. For simplicity I
> didn't include it into "equations" and that's the reason they're not
> equalities, but are proportionalities.
>
>
> >>> 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@email-addr-hidden
> http://lists.linuxaudio.org/listinfo/linux-audio-dev

When I'm in the cinema I sometimes notice unbearable phasing, while a
sound is panned from one 2D position to the other, this isn't a Doppler
effect, but an issue regarding to transit time or something else. IMO
out of phase vs detune.

_______________________________________________
Linux-audio-dev mailing list
Linux-audio-dev@email-addr-hidden
http://lists.linuxaudio.org/listinfo/linux-audio-dev
Received on Thu Jul 29 20:15:03 2010