Path: utzoo!utgpu!attcan!uunet!mcvax!hafro!krafla!raunvis!kjartan
From: kjartan@raunvis.UUCP (Kjartan Pierre Emilsson Jardedlisfraedi)
Newsgroups: comp.graphics
Subject: Re: Sound tracing
Keywords: Sound tracing, accoustics
Message-ID: <240@raunvis.UUCP>
Date: 29 Dec 88 16:02:17 GMT
Organization: Science Inst. Univ. of Iceland
Lines: 73


Hi,

  We would like to begin by thanking everybody for their good replies, which
will in no doubt come handy.  We intend to try to implement such a sound
tracer soon and we had already made some sort of model for it, but we were
checking wether there was some info lying around about such tracers.  It
seems that our idea wasn't far from actual implementations and that is
reassuring.
  
  For the sake of Academical Curiosity and overall Rennaisance-like
Enlightnment in the beginning of a new year we decided to submit our crude
model to the critics and attention of this newsgroup, hoping that it
won't interfere too much with the actual subject of the group, namely
computer graphics.

			The Model:

	We have some volume with an arbitrary geometry (usually simple such
	as a concert hall or something like that). Squares would work just
	fine as primitives.  Each primitive has definite reflection
	properties in addition to some absorbtion filter which possibly
	filters out some frequencies and attenuates the signal.
	  In this volume we put a sound emitter which has the following
	form:

		The sound emitter generates a sound sample in the form
		of a time series with a definite mean power P.  The emitter
		emits the sound with a given power density given as some
		spherical distribution. For simplicity we tesselate this
		distribution and assign to each patch the corresponding mean
		power.

	  At some other point we place the sound receptor which has the
	following form:

		We take a sphere and cut it in two equal halves, and then
		seperate the two by some distance d.  We then tesselate the
		half-spheres (not including the cut).  We have then a crude
		model of ears.

	  Now for the actual sound tracing we do the following:

		For each patch of the two half-spheres, we cast a ray
		radially from the center, and calculate an intersection
		point with the enclosing volume.  From that point we
		determine which patch of the emitter this corresponds to,
		giving us the emitted power.  We then pass the corresponding
		time series through the filter appropriate to the given
		primitives, calculate the reflected fraction, attenuate the
		signal by the square of the distance, and eventually
		determine the delay of the signal.  

		When all patches have been traced, we sum up all the time
		series and output the whole lot through some stereo device.

	    A more sophisticated model would include secondary rays and
	    sound 'shadowing' (The shadowing being a little tricky as it is
	    frequency dependent)


	pros & cons ?
				Happy New Year !!

					-Kjartan & Dagur


--------------------------------------------------------------------------
Kjartan Pierre Emilsson
Science Institute - University of Iceland
Dunhaga 3
107 Reykjavik
Iceland					Internet: kjartan@raunvis.hi.is