On Tue, Sep 20, 2011 at 03:53:08AM +0300, Sampo Syreeni wrote: > On 2011-09-19, Fons Adriaensen wrote: > >>> Though perhaps more surround than most would think. Come with me, >>> here: if you take a look at the compensation circuitry which turns >>> A-format into B-format within the conventional SoundField microphone, >>> isn't it pretty much *exactly* a 3D Blumlein shuffler? >> >> It's not the same. The shuffler is designed to process signals that >> have no significant level differences in the frequency range it >> handles, just the phase differences. > > Like the soundfield above some 10kHz? No?
No. The soundfield capsules are directional, they tend to become even more directional at HF. They produce level differences which are matrixed to obtain the AMB signals. The basic assumption of the matrixing is that everything is in phase, and things would be perfect and require no filtering at all if the capsules could be really coincident. The post matrix filtering is there to partially correct for the effects of non-coincidence, it's a pragmatic compromise and nothing more. As said before, the shuffling algorithm (which amounts to integrating the difference of two pressure signals) is similar to how 'spherical' mics using omnis derive X,Y,Z. Or to the way the B&K intensity probe computes the velocity signal. It *requires* non-coincidence. Normal tetrahral A-format mics do nothing of the sort. > Yes. But the entirety of the soundfield approaches an omni mic at the > very lowest frequencies. Between that 10-12kHz high range and the more > usual 2-4kHz well-optimized range (or so), it's so'n'so. At the very > highest frequencies it again approaches a monopole, because of the > stupendeous amount of spatial aliasing, which then leads to Gerzon's > idea that the energy analysis applies even off-centre, and in fact in > many cases beyond that. Sorry, this makes no sense at all. You seem to be mixing up a lot of concepts without really understanding them. It would be a good idea to return to the mathematical and physical basics, and allow intuition in again only after those are well understood. Ciao, -- FA _______________________________________________ Sursound mailing list [email protected] https://mail.music.vt.edu/mailman/listinfo/sursound
