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Natural Science Forum / Physics / Acoustics / November 2005acoustical parameters for late reverberation of a virtual room
Hey, I'm searching for info on how to acquire acoustical parameters (like RT60) of a given (simple) virtual room for a late reverberation algorithm. I've read some text that suggests using a ray tracing based method for doing this, but i dont quite understand how exactly i should get an IR that way (i understand the basics of ray tracing for image generation), and when i have this IR, how to extract these acoustical parameters. I have found some papers about this topic, but they all belong to www.aes.org, and i dont have access to their papers (i sure would like to :), but my school doesnt have the resources for that, or doesnt want to use it for that, as i am the only comp. science student working on a thesis concerning acoustics). So i'm searching for free info on this topic. Can anyone please suggest a book/paper/site on this topic, thank you. What i do understand about ray tracing to get an IR: i start from the source generating rays, equally distributed on a sphere. I do geometrical reflections and transmissions with that ray (no refractions at the moment). On reflecting on a wall the ray gets the acoustical parameters of that wall (in my case a simple low pass filter), maybe some air attenuation, distance attenuation, and delay caused by distance. But when do i stop, do i take some area in the room where i cumulate the parameters of the rays passing through it? Check out a program like CARA. It's rather cheap and uses (AFAIK) ray tracing to evaluate the room acoustical parameters and show you the soundfields per frequency and other stuff. It is based on a 1/9 log scale in stead of on a musical 1/12 scale (god knows why), but it shows how it is done. It also enables you to choose the amount of reflections used in the calculations; with more reflections the calcs take more time but the definition increase. For very simple calculation of RT there are numerous speadsheets on the web, like here : http://forum.studiotips.com/viewforum.php?f=27 "Professional" programs are Odeon, Ease, and there is a downloadable demo of a program at www.RPGINC.com called catt acoustics Keep in mind that a lot of acoustical engineers have question marks about the validity of these programs. Bert ... > For very simple calculation of RT there are numerous speadsheets on the > web, like here : > http://forum.studiotips.com/viewforum.php?f=27 Thx this was really helpfull, i dont really need a tool for doing it for me, but it helped my to search for the right info and give me some new insights. > "Professional" programs are Odeon, Ease, and there is a downloadable > demo of a program at www.RPGINC.com called catt acoustics > Keep in mind that a lot of acoustical engineers have question marks > about the validity of these programs. > > Bert Hi Emile, > I'm searching for info on how to acquire acoustical parameters (like > RT60) of a given (simple) virtual room for a late reverberation algorithm. as far as I know, reproducing the detailed reflection structure is not very important for modeling late reverb. Probably because reflection density increases with time and therefore each individual reflection has a (much) smaller influence on the perceived result than the early reflection do. Therefore, it should be sufficient to model the early reflections precisely (ray tracing, cone tracing, mirror source modeling) and after some time (depending on the room) replace the precise model with some kind of reverb algorithm that "just" has to mimic the energy decay and reflection density rather than each individual reflection. Best regards, Dieter Michel > Hi Emile, > [quoted text clipped - 13 lines] > with some kind of reverb algorithm that "just" has to mimic the energy > decay and reflection density rather than each individual reflection. this is indeed what im trying to do, to do this i calculate offline the complete IR (and energy decay curve (EDC(t)) or energy decay relief (EDR(t,w))) of my virtual room with some geometrical ray algorithm (ray tracing is often used here because it can be used to model specular and diffusion effects of reflection, and i still dont know how exactly to do this (see original post what aspects i dont understand), then extract parameters like the RT60 from this measured IR and use these as input for a realtime late reverberation algorithm (like a feedback delay network) to shape the late reverb to resemble the measured one. My question was: how to extract these parameters from the measured IR, but i have found some answers for this question in the mean time. thank u for ur response > Best regards, > > Dieter Michel Dieter Michel wrote > Hi Emile > [quoted text clipped - 12 lines] > after some time (depending on the room) replace the precise mode > with some kind of reverb algorithm that "just" has to mimic th energ > decay and reflection density rather than each individual reflection this is indeed what im trying to do, to do this i calculate offlin the complete IR (and energy decay curve (EDC(t)) or energy decay relief (EDR(t,w))) of my virtual room with some geometrical ray algorith (ray tracing is often used here because it can be used to model specula and diffusion effects of reflection, and i still dont know how exactly t do this (see original post what aspects i dont understand), then extract parameters like the RT60 from this measured IR and use these as input for a realtime late reverberation algorithm (like a feedback delay network) to shape the late reverb to resemble the measured one. My question was: how to extract these parameters from the measured IR but i have found some answers for this question in the mean time thank u for ur respons > Best regards > > Dieter Miche |
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