This post refers to Sursound Digest Vol 57 Issue 16 (from) Eric:
A highly-directional mic can be created using omnis and beam forming, but not a *series* of directions at a given instant. (response from) Fons: ??? What would stop anyone from using whatever beamforming algorithm twice (or more times) in parallel, using the same mic signals as input? New thoughts... Hi Fons, It’s not uncommon for me to *underthink* things. I sort-of realized that electrical buffering would allow any of the mics to be used in parallel, even if their respective signals were mixed electrically in any possible combination (to include polarity inversion) or digitally offline. But, I have considered a mic technique that *might* benefit from multiplexing (or its signal processing equivalent). Briefly, I’m a big fan of the Blumlein technique because it gives a wonderful front stage when played through a basic stereo setup. The inherit problem of this technique comes from source-sounds that emanate from behind the mic arrangement (two figure-of-eights, of course). We can’t selectively choose front from back and then swap the rearward sounds’ L-R orientations. The sum and differences of the two bi-directional mics could be manipulated if we got a positive output from both the front and rear lobes simultaneously. This may sound trivial, but this can’t be done in parallel because we don’t have independent outputs for each of the *lobes*. In other words, getting a negative output from a compression to the front could be accomplished via polarity inversion, but this automatically leads to a positive output for a rarefaction to the rear. It *could* (?) be accomplished with the addition of a second pair of mics (starting to sound Ambisonic), but their differences (physical spacing and performance), when compared to the first pair, would create some error, though perhaps not by much. Two *virtual* mics could, in real-time, be created via multiplexing (same as separating odd- from even-numbered samples of a digitized signal?). This leads to a four-channel output from two figure-of-8 mics, which, for the time-being doesn’t get us anywhere. But if the R1, R2, L1, and L2 signals were *appropriately* mixed (e.g. adding R2 to –L1), maybe there’s a way to *get back* the rearward sounds’ proper L-R orientation. As I think about it, the mics would have to digitally swap L and R intermittently (one swap per sample), which won’t work because they have to be physically facing L or R as is required for the Blumlein technique. Well, now that I’ve proven myself wrong (again) while jotting down ideas, I’m going to post this anyway so that others will steer clear from the foibles of poorly conceived ideas. Or, maybe I actually am onto something (unlikely). When I consider the elegant *simplicity* of Ambisonics, it really is a very cool topic: Four mics, and a lot of positive directions! Eric C. -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://mail.music.vt.edu/mailman/private/sursound/attachments/20130423/4c67f3e8/attachment.html> _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
