[LAD] Attenuation of sounds in 3D space

[Ralf Mardorf]

On Wed, 2010-07-21 at 22:07 +0200, JohnLM wrote:
> Continuation of talk from
> Re: [LAD] Floating point processing and high dynamic range audio
> 
> Simply Subject line no longer described the actual content.
> 
> On 2010.07.21. 20:19, Jörn Nettingsmeier wrote:
> > On 07/21/2010 08:56 PM, JohnLM wrote:
> >
> >> If I code program to handle attenuation of sounds depending on their
> >> source (emitter) position in virtual 3D space, I guess then there's no
> >> simple way to relate the effect to real world.
> >> How this is usually handled?
> >
> > you reduce the level with distance (amount depends on whether you are in the near or far field and whether you have a point, line or planar source), and attenuate the high frequencies to simulate air damping. if you're in an enclosed space, you'd also want to take into account the dry-to-reverb ratio, and ideally simulate correct early reflections.
> 
> Thanks! Though this is quite sophisticated. I currently only worry about 
> sound (pressure) level. I will try to implement the rest when the 
> current code actually works.
> 
> Well I have a set of (omidirectional) point sources.
> The code currently has no information whenever given space is open or 
> enclosed. (I guess open or empty space is implied then)
> 
> As much as I can understand the sound pressure is inversely linearly 
> correlated to distance. p~(1/d) or p=k*(1/d) where k is currently 
> undefined constant coefficient.
> 
> What's the thing about far and near fields?
> 
> On Wed, Jul 21, 2010 at 2:01 PM,<fons at kokkinizita.net>  wrote:
> > An audio signal represents pressure variation as a function of
> > time. Multiplying it by two will give 2 times the pressure,
> > and 4 times the power. The subjective result is another matter.
> >
> Ummm... is it sound pressure or sound pressure level? Or it doesn't 
> matter? (are they equivalent?)
> 
> On 2010.07.21. 20:40, Ralf Mardorf wrote:
> > I guess the transit time issue for analog isn't solved. When I worked
> > for Brauner we and SPL developed a surround microphone + SPL mixing
> > console. IMO it's pure bullshit.
> >
> > http://audio.uni-lueneburg.de/seminarwebseiten/audiomedien/frst/material/ICA5.jpg
> > http://audio.uni-lueneburg.de/seminarwebseiten/audiomedien/frst/material/asm5.jpg
> >
> > Perhaps today there is math for virtual effects, I don't know, but I
> > would be very sceptic.
> >
> 
> I'm sure any digital alogrithm are far from perfect to represent the 
> acoustic attenuation (and related) effects like in real world. But it 
> just need to be close enough.
> 
> Ummm... I somehow fail to see how the microphone rig is related to this.

This is around 10 years ago, it might be that a lot of issues are solved
today. Anyway, regarding to psycho-acoustic the artificial head, just
stereo, isn't that bad.

Just keep in mind that we have two ears and any math or analog recording
with more virtual ears is suspect, regarding to a natural impression.

JUST 2 cents,

Ralf