[Sursound] reinvention of the wheel??
Just received an email which - seems someone else is reinventing the Soundfield again - see http://www.quaud.io/ This time it's based on mems microphones and is very small so it ends up using blind source separation in order to get good source-interference ratios. There's only one reference to Gerzon and Craven in their papers, the latest one, and it's only brief - and no mention at all of Villa Pulkki's work which seems closely related. Interesting... Dave -- As of 1st October 2012, I have retired from the University, so this disclaimer is redundant These are my own views and may or may not be shared by my employer Dave Malham Ex-Music Research Centre Department of Music The University of York Heslington York YO10 5DD UK 'Ambisonics - Component Imaging for Audio' -- next part -- An HTML attachment was scrubbed... URL: <https://mail.music.vt.edu/mailman/private/sursound/attachments/20130420/2690b8c2/attachment.html> ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Optimised Decoder matrix (Ambdec)
I agree with Fons here. We have used essentially this approach when we needed to play back Ambisonic material on The Morning Line (which is very irregular and needs preferably to use VBAP) right from when we first set it up back in 2008 and you definitely won't find it easy to get it work optimally - manual tweaking is pretty well always needed. However, at this stage, there probably isn't a better approach for low order Ambisonics, either automatic or manual. Dave On 19 April 2013 23:33, Fons Adriaensen wrote: > On Fri, Apr 19, 2013 at 10:12:20AM -0700, Aaron Heller wrote: > > > F. Kaiser, “A Hybrid Approach for Three-Dimensional Sound > Spatialization,” > > Algorithmen in Akustik und Computermusik 2, SE, May 2011. > > > http://iaem.at/kurse/winter-10-11/aac02se/2011_Kaiser_SeminararbeitVersatileAmbisonicDecoder.pdf > > > > > > The toolkit reads speaker locations from CSV files (and other formats, > > including ambdec presets) and writes out presets files for Fons' Amdec > > decoder. There's also an initial implementation of a Faust backend, that > > produces decoders that can be compiled to VST, Supercollider, Pd, MaxDSP, > > ...(see http://faust.grame.fr/ for more about Faust). > > > > AllRAD is a hybrid ambisonic/vbap technique, especially suited to > irregular > > arrays. The idea is you design a decoder for a regular array (in this > > case a 240 virtual speaker spherical design) and then map those signals > to > > the real array using Pulkki's VBAP. > > This is one of the many methods I tested, and rejected. If applied > 'blindly' it can easily produce rather suboptimal results (*) - as > would any method that in the end amounts to linear combinations of > the outputs of a 'regular layout' decoder. Things improve if the > VBAP gains are adjusted manually, but that more or less defeats the > purpose of an 'automatic' method, and even results obtained that way > are suboptimal. > > The problem behind this that adding VBAP (or any other) pannings of > (partially) correlated signals will not produce the correct result > - at least not in the frequency range where rE magnitude and direction > are the metrics. There are solutions to this, but they are not simple. > > Ciao, > > > (*) Try for example a 5th order horizontal decode to a regular ring > of 12 speakers, then remove one of them and it replace by a VBAP > panning into the two nearest ones. > > > -- > 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 > Sursound@music.vt.edu > https://mail.music.vt.edu/mailman/listinfo/sursound > -- As of 1st October 2012, I have retired from the University, so this disclaimer is redundant These are my own views and may or may not be shared by my employer Dave Malham Ex-Music Research Centre Department of Music The University of York Heslington York YO10 5DD UK 'Ambisonics - Component Imaging for Audio' -- next part -- An HTML attachment was scrubbed... URL: <https://mail.music.vt.edu/mailman/private/sursound/attachments/20130420/da26/attachment.html> ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
[Sursound] Re-re-inventing the wheel
Just received an email which - seems someone else is reinventing the Soundfield again - see http://www.quaud.io/ This time it's based on mems microphones and is very small so it ends up using blind source separation in order to get good source-interference ratios. There's only one reference to Gerzon and Craven in their papers, the latest one, and it's only brief - and no mention at all of Villa Pulkki's work which seems closely related. Interesting... Dave Hi Dave, That is interesting... but then, too much info might preclude their getting a patent? I did notice that the mic in question uses omnidirectional capsules. I'll have to re-re-read the literature by Gerzon, Craven, et al. I recall that Gerzon's earliest ideas depended on figure-of-eight mics (akin to Blumlein Stereo), whereas all later incarnations use subcardiod mics. Whether this is of any consequence or not... I don't know. Does beam forming or delay techniques to create additional first-order patterns from the omnidirectional mics change up the design (and math) from arrays using intrinsically cardiod mic elements? Anyway, I certainly hope credit will go to where credit belongs. Long live Ambisonics! Eric C. PS--I look forward to listening to the YouTube samples of from the aforementioned link. I hope it's not another helicopter. Or worse, a barber shop scenario. -- next part -- An HTML attachment was scrubbed... URL: <https://mail.music.vt.edu/mailman/private/sursound/attachments/20130420/1a2206ba/attachment.html> ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Re-re-inventing the wheel
At 11:24 20-04-13, Eric Carmichel wrote: >Just received an email which - seems someone else is reinventing the >Soundfield again - see http://www.quaud.io/ >This time it's based on mems microphones and is very small so it ends >up using blind source separation in order to get good >source-interference ratios. There's only one reference to Gerzon and >Craven in their papers, the latest one, and it's only brief - and no >mention at all of Villa Pulkki's work which seems closely related. >Interesting... >Dave > >Hi Dave, >That is interesting... but then, too much info might preclude their >getting a patent? I did notice that the mic in question uses >omnidirectional capsules. I'll have to re-re-read the literature by >Gerzon, Craven, et al. I recall that Gerzon's earliest ideas depended >on figure-of-eight mics (akin to Blumlein Stereo), whereas all later >incarnations use subcardiod mics. If one regards the subcardioid as made up of omni and figure of eight components, is it not the case that the ambisonic XYZ signals of the Soundfield Mic are derived solely from the figure of eight components? Further, if this new mic relies on omni capsules, how will it not suffer from the signal to noise ratio problem of Blumlein's method of deriving stereo from two omnis? David ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Re-re-inventing the wheel
SNR wouldn't have been my initial concern because I have some wee-tiny electrets that have (purportedly) +10 dBA noise--pretty low for a small capsule. When I think of the "classic" multi-polar mics such as the AKG-414, the multiple patterns are often derivatives of back-to-back diaphragms sharing a common stator (I think... not a mic expert here). In comparison, ribbon mics (Coles, Royer, vintage RCA, etc.) are figure-of-eight (or bi-directional) because of their pressure-gradient design. Cardiod condenser and dynamic mics have rear venting for delay/cancellation (delay using materials of varying density, not merely time-in-air delay), hence their directional characteristics. So... Having directional characteristics provides direction-dependent output levels for each of four mics. Spacing, of course, provides a time difference component for computing direction. The ideal is no inter-capsule spacing (= zero time delay). Tightly spaced omnis are just that... omni... and wouldn't have discernible time or level differences unless there's *some* time difference or pressure difference. Sound intensity probes rely on a phase (and level) difference to determine the vector quantity of sound power (SPL alone being a scalar quantity). So, based on acoustical signal processing and beam forming described by, for example, Vorlander, I was curious whether the *new* surround mic used such processing to create four virtual subcardiods that would also serve as the equivalent *A-format* mics. Any single mic, or average of all mics, would be the omni component. For mics such as the AKG 414, the electrically and acoustically combined response yields one polar. So, I was really wondering how four omni mics could provide unique info for multiple directions. A highly-directional mic can be created using omnis and beam forming, but not a *series* of directions at a given instant. Now, scratching my head, there's no reason that multiplexing among the mics couldn't be used to create rapidly-changing patterns that are akin to interleaved quad channels. That is to say, only one direction is picked up at a time, but the derived direction changes swiftly enough that it appears to have four *directional* mics (is this a new idea... it just came off the top of my head... most of what I think up has been done.) I just found the technology interesting/curious, and wondered where it might deviate from the Soundfield mic to the point of being a unique design. One aspect of a patent is that the invention be unique. Above post in response to:: If one regards the subcardioid as made up of omni and figure of eight components, is it not the case that the ambisonic XYZ signals of the Soundfield Mic are derived solely from the figure of eight components? Further, if this new mic relies on omni capsules, how will it not suffer from the signal to noise ratio problem of Blumlein's method of deriving stereo from two omnis? David -- next part -- An HTML attachment was scrubbed... URL: <https://mail.music.vt.edu/mailman/private/sursound/attachments/20130420/8684942d/attachment.html> ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Re-re-inventing the wheel
On 2013-04-20, Eric Carmichel wrote: Does beam forming or delay techniques to create additional first-order patterns from the omnidirectional mics change up the design (and math) from arrays using intrinsically cardiod mic elements? Not per se, as we can see from designs like the Eigenmike. However, it does lead to hugely wasteful use of microphones compared to letting physics do the basic job of discriminating between waves going in opposite directions. Especially so since there's a topological problem with extended arrays which aren't internally sampled to the spatial aliasing limit. (I think it was Filippo who first raised this one.) If you think about a spherical array of omnis on the one hand and omnis mounted on a sphere (or cardioids) on the other, the latter has a topological hole in the center whereas the former does not. The sphere of directions has that hole too, so if you forget about W for a second, those holes topologically have to map to each other when going from the array signals to the spherical harmonic representation (finite dimensional linear maps are continuous, so they preserve holes). That means that your A-format to B-format transform will necessarily end up mimicing that singularity, and that's expensive in mic terms. (As a whole, the hole ain't there because once you add W, it kind of patches over it. But that doesn't much help you when you consider the derivation of each 1+ order signal in isolation.) The nasty side effect of that is that knowing the field over a sphere doesn't uniquely determine the field inside the sphere, whereas knowing the field and that there's a rigid ball in the center (the singularity, the hole) in addition does get you there. The same goes for knowing both the pressure field and its normal velocity, or knowing the outwards pointing cardioid response, because in both cases you can easily synthesize the singularity. If you only work with monopoles in the free field, eventually you'll end up simulating the dipole (velocity) component, at the cost of extra mics, plus spatial aliasing concerns force you to oversample in space. Effectively you have to go look inside the sphere in order to fully determine the field there, whereas it would have been enough to look just at the border if there was some physical mechanism which gained direct access to the velocity component of the field, like an obstruction giving rise to a cardioid response, a genuine velocity measurement like a MicroFlown, or that rigid sphere in the center which mixes pressures and velocities by imposing a boundary condition of zero normal velocity. Okay, that's almost abstract nonsense and it took ages for me to grasp what was going on, so let's look at it from another perspective. How could two fields with the same boundary pressure field happen? The secret is a special kind of standing wave with full spherical symmetry. If you have that, you can place one of the antinodes (a full sphere) right at your microphone rig boundary. If the mics are monopoles, they won't sense the field at all, so that means any field with this property can be freely added to any other field without the A-format changing. If you had access to normal velocity as well, all of the information would be there, but if you only have pressure sensitive monopoles, you'll necessarily have to place some of them inside the sphere to tell the difference. And if you think about it, that special field is not just a harmless corner case: it's composed of all the modes of a spherical cavity under the boundary constraint of zero pressure (plus a matching, uniquely determined field outside the sphere); if you want to tame them all, you pretty much have to sample the whole interior to some highish spatial frequency limit. The same can't happen once you put a singularity in the middle, which is what outwards pointing cardioids too end up doing. Then the remaining modes are topologically speaking those of a sphere, not those of a ball, and monopoles suffice to capture them. I'm also pretty sure this is connected to some nasty algebraic weirdness (spin groups as double covers of their orthogonal counterparts) through the NFC-HOA papers, because in the latter the sphere of directions is covered twice with not only an incoming but also an outgoing field (cardioids pick one, a full Kirchhoff-Helmholtz integral can represent both) which too patches the hole. Dunno how the details might work out, though. -- Sampo Syreeni, aka decoy - de...@iki.fi, http://decoy.iki.fi/front +358-50-5756111, 025E D175 ABE5 027C 9494 EEB0 E090 8BA9 0509 85C2 ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Re-re-inventing the wheel
On 2013-04-20, David Pickett wrote: If one regards the subcardioid as made up of omni and figure of eight components, is it not the case that the ambisonic XYZ signals of the Soundfield Mic are derived solely from the figure of eight components? Not quite, because at high frequencies the mics aren't exactly coincident, so that the following A-to-B matrix derives some of W from the fig-8 (or velocity) components and some of XYZ from the monopole contributions. But almost: XYZ are conceptually just three fully coincident fig-8's, sensitive purely to velocity (and derivable in this case from pressure gradient over time). Further, if this new mic relies on omni capsules, how will it not suffer from the signal to noise ratio problem of Blumlein's method of deriving stereo from two omnis? It most likely does, or it has to compensate with an extended array of omnis, adding to cost. -- Sampo Syreeni, aka decoy - de...@iki.fi, http://decoy.iki.fi/front +358-50-5756111, 025E D175 ABE5 027C 9494 EEB0 E090 8BA9 0509 85C2 ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Re-re-inventing the wheel
At 15:27 20-04-13, Sampo Syreeni wrote: If one regards the subcardioid as made up of omni and figure of eight components, is it not the case that the ambisonic XYZ signals of the Soundfield Mic are derived solely from the figure of eight components? Not quite, because at high frequencies the mics aren't exactly coincident, so that the following A-to-B matrix derives some of W from the fig-8 (or velocity) components and some of XYZ from the monopole contributions. But almost: XYZ are conceptually just three fully coincident fig-8's, sensitive purely to velocity (and derivable in this case from pressure gradient over time). But... How close to the theoretical A format polar diagramy are the XYZ components of the Soundfield (or Tetramic) microphone at frequencies above those at which they are essentially coincident? At 15:08 20-04-13, Eric Carmichel wrote: >SNR wouldn't have been my initial concern because I have some wee-tiny >electrets that have (purportedly) +10 dBA noise--pretty low for a small >capsule. Granted this is better than the mics that Blumlein could command, but when it comes to the processing of the raw outputs, is not the problem of lower level signals produced by subtraction still a real one? David ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Re-re-inventing the wheel
On 2013-04-20, David Pickett wrote: But... How close to the theoretical A format polar diagramy are the XYZ components of the Soundfield (or Tetramic) microphone at frequencies above those at which they are essentially coincident? Rather far from them, because the ideal A format response is a) a mixture of pressure and velocity and b) not even a 1-1 mix for a cardioid. However, they are essentially perfect representations of the true XYZ velocities (ideal B-format) to about 10kHz, where the 3.3cm wavelength approaches the mic diameter. So, pretty darn good, considering, and even beyond that at least the intensity response stays controlled. Well implemented the classical tetrahedral design is an outstanding realization of the theory. -- Sampo Syreeni, aka decoy - de...@iki.fi, http://decoy.iki.fi/front +358-50-5756111, 025E D175 ABE5 027C 9494 EEB0 E090 8BA9 0509 85C2 ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] reinvention of the wheel??
Dave Malham wrote: > Just received an email which - seems someone else is reinventing the > Soundfield again - see http://www.quaud.io/ > This time it's based on mems microphones and is very small so it ends up > using blind source separation in order to get good source-interference > ratios. There's only one reference to Gerzon and Craven in their papers, > the latest one, and it's only brief - and no mention at all of Villa > Pulkki's work which seems closely related. Interesting... See also their US Patent Application 20110015924, ACOUSTIC SOURCE SEPARATION http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PG01&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.html&r=1&f=G&l=50&s1=%2220110015924%22.PGNR.&OS=DN/20110015924&RS=DN/20110015924 This was the only US Patent or US Patent Application that I could find by this team. Regards, Martin -- Martin J Leese E-mail: martin.leese stanfordalumni.org Web: http://members.tripod.com/martin_leese/ ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Re-re-inventing the wheel
I truly appreciate your informative and highly detailed response. For helping understand spherical harmonics (or Legendre polynomials?), and for mics lying on surface of a sphere, this helps a lot. But here's what I don't understand about the quaud (quaud.io) mic: They say the four omnidirectional mics lie on the corners of a tetrahedron--essentially same arrangement as Soundfield, but with omni mics and positioned on corners of tetrahedron. Re mics on a sphere: In a corner-oriented tetrahedral arrangement, the mics would lie on a *virtual* sphere just as much as mics on a sphere could be lying on a virtual tetrahedron. But at some point the actual (physical) surface becomes a piece of the whole. This is clearly evident when the sphere is large enough to be a human head. So I'm not always clear as to whether it's the mics' virtual orientation in space, or the physical boundary of a spherical surface, that *shapes* the sound and creates the requisite time and pressure differentials. Dave M's original post states that someone else is... again... re-inventing the Soundfield mic. I'm sure that I'm not the only person who is curious as to what makes the quaud (Trademark) mic *unique* and different from the Soundfield mic--particularly if the quaud mic is patented. Is, for example, more than one tetrahedral arrangement used to achieve *surround* spacing--which would then be a wholly different thing? I need to read further. Thanks again for info. The following was cut-and-pasted from their website (I think Dave provided all of this in his post, too): quaudio comprises four omnidirectional microphones located at or near to the corners of a regular tetrahedron. Since these capsules are omnidirectional they can be located at the opposite corners of a cube with no loss in generality. This arrangement is straightforward to achieve in a standard PCB assembly line by soldering two pairs of MEMS or electret capsules on opposite sides of the substrate. Alternatively it is possible to solder three capsules to one side and a single capsule to the other. In both cases the acoustic centre of each sensor should be separated laterally by a distance corresponding to the vertical separation between membranes on either side of the device -- next part -- An HTML attachment was scrubbed... URL: <https://mail.music.vt.edu/mailman/private/sursound/attachments/20130420/263f0c70/attachment.html> ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Re-re-inventing the wheel
On Sat, Apr 20, 2013 at 01:08:57PM -0700, Eric Carmichel wrote: > A highly-directional mic can be created using omnis and beam > forming, but not a *series* of directions at a given instant. ??? What would stop anyone from using whatever beamforming algorithm twice (or more times) in parallel, using the same mic signals as input ? 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 Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Re-re-inventing the wheel
On Sat, Apr 20, 2013 at 03:49:22PM -0500, David Pickett wrote: > Granted this is better than the mics that Blumlein could command, > but when it comes to the processing of the raw outputs, is not the > problem of lower level signals produced by subtraction still a real > one? It certainly is. The problem is not just noise, but also gain calibration and stability. 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 Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Re-re-inventing the wheel
On Sat, Apr 20, 2013 at 02:38:42PM -0700, Eric Carmichel wrote: > So I'm not always clear as to whether it's the mics' virtual > orientation in space, or the physical boundary of a spherical > surface, that *shapes* the sound and creates the requisite time > and pressure differentials. Omni mics don't have any orientation, so its only the pyhsical shape they are mounted on that would create directivity and time differences. For a 'classic' soundfield mic it is mostly the mic's polar pattern that leads to differences between the A-format signals, except at HF where the physical size and shape of the array comes into play (which is an unwanted thing in this case). Regarding Quaudio there is some confusion (or obfuscation) going on as two things get mixed up: the mic (which apart from its small size is not really anything new), and the processing used to separate sources (which has some novel elements). Regarding the latter, in the papers it is stated that the same algorithm can be used with a standard tetrahedral mic - the required input is B-format. The separation method proposed seems to rely on long-term statistics of the intensity vector, which would mean it can't be used for e.g. moving sources. The test cases documented are for one, two or three static sources. 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 Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Re-re-inventing the wheel
On 2013-04-20, Eric Carmichel wrote: But here's what I don't understand about the quaud (quaud.io) mic: They say the four omnidirectional mics lie on the corners of a tetrahedron--essentially same arrangement as Soundfield, but with omni mics and positioned on corners of tetrahedron. For a near-coincident array this is not such a problem, because if you think about the modes which might fit within it, they happen at such high frequencies (above 10kHz) that we can largely neglect them. In this very special first order only case, you can approximate three pressure gradients (and by filtering them, velocities XYZ) and an average pressure (W) using for monopoles as well. In this case the mic itself is the singularity and the physics doing the heavy lifting is the fact that soundfields do have four independent degrees of freedom even pointwise; the first four ambisonic components are present even in a point, and even if you approximate the directional ones by differences of monopoles, you can get the job done. In the theoretical sense the price you pay is reduced sensitivity at low frequencies, which leads to noise amplification when you do the differencing. Practically the mic assembly itself is a physical barrier which gives you some leverage -- and in this case they're actually talking about mounting the whole thing on the surface of a PCB too. The trouble with inwards and outwards propagation goes away because there is no inside in a coincident array. So, the mic itself is nothing new, just yet another realization of a soundfield mic, quite possibly cheaper but also less sensitive at LF due to size. The real contribution appears to be in the source separation algorithm. For that they do an intensity analysis in the Fourier domain much like DirAC does. Then they apply a sizable bank of beam forming filters in all directions under a planewave assumption, which is one way to do infinite order decoding (in older forms called steering, or a nonlinear, dynamic matrix). Finally instead of picking one of the beamformers per source they do a principal component reduction and pick the leading eigenterms. The combination of the last two steps is essentially equivalent to just doing nonorthogonal factor analysis of the instantaneous directions of arrival we got from the real (propagating, nonreactive) part of thefirst step, except that the second step helps us avoid a number of basis selection problems (or permutation problems as the authors call them) so that coherent sources stay together. That sort of stuff always works as long as the problem is at most complete, which is why with four mics they never try to go beyond three or four sources. Any extra sources -- from reflections and the like -- will end up being distributed into the derived signals based on the eventual virtual mic patters. In this kind of a system those patterns are then pretty haphazard in that while they yield maximum response towards each of the first four estimated sources (arbitrary directionality) and each pattern gets a null in the direction of the other three, in between the directions there is zero control of sidelobe direction (its maxima are somewhere in the direction of the reciprocal overcomplete "basis", i.e. highly unpredictable if the sources deviate from tetrahedral placement) or amplification. In general that sort of thing probably shouldn't be analysed in the spherical framework in the first place, but simply as a MIMO beamforming problem with rigid spacing of nulls. Such things yield optimal separation of direct sound, but in a busy space they can royally mess up reverb and especially any attempts at recombination of the derived signals (there's frequency selectivity and maybe phase stuff going on here as well, so in that sense similar to SRS's to-5/7.1 upconversion stuff, which I wouldn't easily use in a studio environment but at most as an active matrix). This is clearly evident when the sphere is large enough to be a human head. So I'm not always clear as to whether it's the mics' virtual orientation in space, or the physical boundary of a spherical surface, that *shapes* the sound and creates the requisite time and pressure differentials. Omnis obviously don't have any directionality. Cardioids (and most fig-8's) derive their directionality (i.e the mixing stuff) from their physical design, which has a boundary, with its boundary conditions, somewhere. E.g. the capsules used in a SoundField carry their own "wall" with them. MicroFlowns and the like are the exception because they touch velocity directly. -- Sampo Syreeni, aka decoy - de...@iki.fi, http://decoy.iki.fi/front +358-50-5756111, 025E D175 ABE5 027C 9494 EEB0 E090 8BA9 0509 85C2 ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
