The rear lobes of a figure-8 decode in VVMic should be inverted just like those of a physical figure-8 mic. It's a linear decoder and not really capable of anything else. Harpex, being a parametric decoder, could be producing a figure-8 pattern with non-inverting rear lobes, or with the rear lobes swapped, but I doubt they do. Someone with the Harpex plugin could test this by panning an impulse into one of the rear lobes and checking the results.
I'd say it's more likely that some subtle combination of the spatial aliasing from the large array with the parametric decoder in Harpex is producing different results than a linear decode of the same spatial aliasing. Neither can really be correct in the upper, aliased part of the spectrum and so it's not surprising to me that they would sound different. This could be tested by filtering out frequencies above the aliasing point, though with an array that large this will be pretty low (~2kHz?). I might also suggest, as a point of comparison, to test against a simple mix of the inputs. Ignoring fine points like shelf filters and NFC, a figure-8 decode is simply L=X+Y, R=X-Y. David McGriffy VVAudio.com On Mon, Jun 15, 2015 at 5:51 PM, Gerard Lardner <glard...@iol.ie> wrote: > That occurred to me too. The Oktava array is really huge (mine is an old > one; the newer ones may be smaller); it places the capsules on a sphere of > radius 48 mm - nearly 4" diameter! But the problem, the swapping of left > and right in the front soundstage, exists only for one decoder (of those > that I have tried) and only for one virtual mic pattern - VVmic decoding > B-format to Blumlein stereo pair; it doesn't occur if I use Harpex B Player > to decode the B-format to the same Blumlein stereo pair. That's what is > puzzling. If they were swapped in more cases I could perhaps understand it > better. I was wondering if VVMic and Harpex treat the 'back' lobes of the > crossed figure-8s differently. > > When I have some more time, I will try to record something using both the > Oktava array and a Brahma Ambisonic mic and to see if there is the same > difference. The Brahma array is much smaller than the Oktava array. > > Gerard Lardner > > > On 14/06/2015 17:34, Paul Hodges wrote: > >> --On 13 June 2015 20:15 +0100 Gerard Lardner <glard...@iol.ie> wrote: >> >> I recorded a concert using my Oktava MK-012 4D ambisonic microphone >>> and encoded it to B-format using Brahmavolver. Yesterday, while >>> playing back the recording with the conductor we noticed that under >>> certain circumstances left and right appeared to be swapped. >>> >> My first thought is that the microphone used has its capsules more >> widely spaced than other tetrahedral mics, which could be leading to >> some directivity confusion at lower frequencies than usual, which in >> turn this material might be sensitive to. Certainly I've never noticed >> such an effect with VVmic, whether using a TetraMic or my previous >> native B-format arrangement. >> >> Paul >> >> > _______________________________________________ > Sursound mailing list > Sursound@music.vt.edu > https://mail.music.vt.edu/mailman/listinfo/sursound - unsubscribe here, > edit account or options, view archives and so on. > -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://mail.music.vt.edu/mailman/private/sursound/attachments/20150616/f9291613/attachment.html> _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound - unsubscribe here, edit account or options, view archives and so on.
