There are dual-diaphragm (von Braunmuhl & Weber design) mics where the each signal is brought out separately, such as the Pearl TL44 or Neumann QSM69, giving you back-to-back cardioids. By taking the sum and difference you can get a fig-8 and omni simultaneously from the same mic. Add a second mic at right angles and you have a natural horizontal B-format array (WXY). Martin Kantola's Panphonic microphone works this way: http://www.panphonic.com/
Aaron Heller (hel...@ai.sri.com) Menlo Park, CA US On Tue, Apr 23, 2013 at 12:45 PM, Eric Carmichel <e...@elcaudio.com> wrote: > 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 > -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://mail.music.vt.edu/mailman/private/sursound/attachments/20130423/68415083/attachment.html> _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
