[LAD] Attenuation of sounds in 3D space

[fons at kokkinizita.net]

On Wed, Jul 21, 2010 at 10:07:10PM +0200, JohnLM wrote:

> What's the thing about far and near fields?

The rule   pressure = 1 / distance  is true only for
theoretical point sources, and for real sources if the
distance is much larger than the size of the zource.
In the other case you are in the 'near field' where
things can get quite complex.

For some sounds you are almost always in the 'near' field
e.g. a highway with many moving cars on it, the seashore,
etc. These are essentially large line sources with many
independent sound generators which blurr into a single
sound, and in that case you'd get different relations,
e.g.  pressure = 1 / sqrt(distance).

> 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?)

The term 'sound pressure level' (SPL) usually refers to sound
pressure measured in a standardized way. 

What you try to do is called spatialization. It involves
modelling the directivity and motion of the sources and
their interaction with the space they are in, and it can
get arbitrarily complex.
Software to do this in specialised cases (e.g. electronic
music) exists. More general solutions and in particular
practical systems (allowing complex and dynamic scenes)
are still a research topic, e.g. at Barcelone Media.

Ciao,

-- 
FA

There are three of them, and Alleline.