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 > [email protected] > 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 [email protected] http://lists.linuxaudio.org/listinfo/linux-audio-dev
