Hi Steve, Thanks for your comments on impulses, etc. My main concern was that, and I'm sure you know this perfectly well, that mathematical physicists are fond of saying about impulses, in the context of integration, that the shape of the impulse doesn't matter too much. It's a handy way to sweep away a difficult derivation! This is true for many physical phenomena. But in audio --- and again I'm sure you know this but others may not --- the ear is an extraordinarily sensitive detector, and audio includes many different physical situations, sometimes on very short time scales. So I think it's important to ensure that everyone understands that "doesn't matter too much" doesn't necessarily mean "isn't audible." --------------------------------- (The following is more specific, hopefully of interest to at least some LAUer's.) On my web page is a song "latest" that uses calculated IR's. Some software is there to produce them, also. But I know you're a busy guy! The song "latest" is for headphones, as usual. Long ago you and some others encouraged me to post the IR generators. They were so user unfriendly that I took some time to "put some lipstick" on them. Hopefully they're not too bad now. Regarding synthetic space --- ironically a problem with the Green's function technique that I'm using, the calculated IR's are a little too accurate. They have extremely sharp spikes, and the timing is very accurate. You can hear echos where you might actually hear more of a reverb (with actual diffuse reflections). Amplitudes can also become very large, yet the sound have very little power. Here again, I think that diffusion and diffuse reflections need to be incorporated, or something mimicing them. However, this accuracy produces crystal clear sound, and I find more and more that I like it compared to the mushy sound that a lot of audio software produces. Some reverb models sound hilarious to me because they're so physically erroneous. I can't hear the music over the sound of my own laughter. I'm not a big fan of ray-tracing at this time. It just seems to me that it's equivalent to a sparse grid without some sort of optimization or pruning method. But I have no experience other than reading technical articles. I've worked in the semiconductor industry with finite difference codes, so naturally it occurs to me to try and build a IR generator using that technique. Do you have any experience along those lines? Please feel free to contact me via email if you prefer, because that's probably not of interest to LAUer's. My crude estimates lead to a monstrous mesh and no chance of reducing the time step. This may be OK for IR generation... Thanks for any further comments. Best regards, Dave.