On Wed, Dec 19, 2012 at 09:28:56AM -0800, Eric Carmichel wrote: > Although a second website now seems to have vanished, there was > a site that hosted the Ambisonic IRs for a classroom, Great Hall, > and Octagon.
It seems the site is still available. Anyway I found the Great Hall and Octagon in my archives, along with a readme.txt which says: "These IRs are released under the Creative Commons Attribution- Noncommercial-Share-Alike license with attribution to the Centre for Digital Music, Queen Mary, University of London." Another matter is how to prepare 'raw' AMB IRs for actual use. The procedure I normally follow is: * Apply a highpass filter to remove any VLF noise. * Find the 'direct sound' impulse. Measure its RMS value. Apply gain to all channels so this value is equal to the W-channel gain of your panners (i.e. 0.707 if you use FuMa) Apply additional gains to X,Y,Z in case you don't use FuMa. * Check the FR of the direct sound impulse. It should be reasonably flat if the IR was corrected for speaker response using a separate measurement with an omni mic. * Cut the beginning of the file so the first sample is at the start of the direct sound, and remove the entire direct sound impulse. Optionally zero the first 20 ms or so. Anything there just colours the sound without contributing to the spatial effect. This leaves you with an IR that can be used directly as an 'post-fader aux send' reverb. If the sidechain (i.e. the convolver) has zero dB gain you get the correct wet/dry ratio for the position of the speaker used to make the measurement. If you use a tool such as jconvolver (Linux) you don't need to touch the original files as all the above gains and editing can be done by parameters in the preset file. Ciao, -- FA A world of exhaustive, reliable metadata would be an utopia. It's also a pipe-dream, founded on self-delusion, nerd hubris and hysterically inflated market opportunities. (Cory Doctorow) _______________________________________________ Sursound mailing list [email protected] https://mail.music.vt.edu/mailman/listinfo/sursound
