Re: [Sursound] Why do you need to decode ambisonic/b format signals ?
Hi Robert, On 24.01.2011, at 06:26, Robert Greene wrote: > Does anyone really like the sound of the human voice > from four inches away for example? Actually that's quite a distance ;-) Really, spot miking can come in handy. Sometimes you want to capture an intimacy that can only be had at close distance, e.g. with the flutes on my Zen-album (http://flow.blumlein.net/010_gb.html) I wanted to preserve the very soft blowing sounds. I even used the sound of breathing / the air with nearly no tone to bridge separate tracks. Almost inaudible yet more substantial than the dither-noise (I picked for this release). > Audio people act as if the master were the word of God. > But the master is in fact usually lousy. With sonophiles, people who take sound seriously, the high resolution master is fine and certainly better than most versions that can be released on traditional carriers. Regards, Andrew ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Why do you need to decode ambisonic/b format signals ?
Of course. Except that when everyone makes recordings the wrong way, then people are likely to prefer the recordings played back a complementary wrong way. Why would anyone want to hear most commercial recordings as they actually are? Does anyone really like the sound of the human voice from four inches away for example? Audio people act as if the master were the word of God. But the master is in fact usually lousy Robert On Mon, 24 Jan 2011, Ronald C.F. Antony wrote: On 23 Jan 2011, at 23:52, Robert Greene wrote: Of course this completely ignored the fact that in blind testing years ago, everyone preferred cassettes of vinyl to vinyl itself(which ought to have told people something about the recording industry's recording practices). Sounds like they were using DDM vinyl ;) Besides, some people like euphonic distortion like tape saturation. But such things should always an effect used during production, not a side-effect introduced by the delivery medium. So even if cassette sounds "better" it's still worse, because it should sound like what was mastered, and if the cassette sound is the target sound, then that's how the master tape should sound. It shouldn't be introduced in playback. Therefore all "better sound" that's introduced by the medium or equipment. Anything that doesn't exactly sound like the original master is sounding worse, by the very definition that it diverges from the master. If you don't like how the master sounds, yell at the mastering engineer, don't screw with euphonic playback equipment. Ronald ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Why do you need to decode ambisonic/b format signals ?
I have a photo of my great grandfather's house in Germany with my great grandfather standing in front of it. Try that with a digital photo on a memory stick in a hundred years(which is roughly how old the photo is--a bit older actually). Books, pictures, records endure. Digital information is here today gone tomorrow. And don't let anyone tell you different. On the other hand, thanks to the internet, I could see my greatgrandfather's house as it is today --or at least I could until the link gave out. Fortunately, I downloaded the photo! (It is a grandiose house--I was teasing my wife about how the family has fallen on hard times) Robert On Sun, 23 Jan 2011, Eero Aro wrote: True, so true - not something I'd choose, but. I'll go downstairs and wind up my HMV Gramophone from 1905, it's still working. Will my mp3 player do the same after 100 years? Eero ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Why do you need to decode ambisonic/b format signals ?
On 23 Jan 2011, at 23:52, Robert Greene wrote: > Of course this completely ignored the fact > that in blind testing years ago, > everyone preferred cassettes of vinyl > to vinyl itself(which ought to have > told people something about the recording > industry's recording practices). Sounds like they were using DDM vinyl ;) Besides, some people like euphonic distortion like tape saturation. But such things should always an effect used during production, not a side-effect introduced by the delivery medium. So even if cassette sounds "better" it's still worse, because it should sound like what was mastered, and if the cassette sound is the target sound, then that's how the master tape should sound. It shouldn't be introduced in playback. Therefore all "better sound" that's introduced by the medium or equipment. Anything that doesn't exactly sound like the original master is sounding worse, by the very definition that it diverges from the master. If you don't like how the master sounds, yell at the mastering engineer, don't screw with euphonic playback equipment. Ronald ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Why do you need to decode ambisonic/b format signals ?
Definitely not, and none of the things that were recorded that way will be playable except by archivists. But that is fair enough since none of the music being provided that way will be of any interest to anyone except cultural(using the word loosely) historians anyway. Robert On Sun, 23 Jan 2011, Eero Aro wrote: True, so true - not something I'd choose, but. I'll go downstairs and wind up my HMV Gramophone from 1905, it's still working. Will my mp3 player do the same after 100 years? Eero ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Why do you need to decode ambisonic/b format signals ?
Actually, I think the remarks below represent a bit of a misconception about stereo playback. In actuality, if one used more speakers one could make stereo playback better in the sense that one could widen the spot in which it sounded reasonably correct. In actuality, if one sits absolutely still in a controlled environment(clamped head anechoic listener) then one can create ay sonic impression desired with two speakers. The real question is what works in a reasonably stable way since very few people are willing to clamp their heads! (Actually, physical clamping is not necessary-the Carver Sonic Hologram works if one just sits really still in the right spot. But the right spot is very narrowly specificed!) Robert On Sun, 23 Jan 2011, Martin Leese wrote: Augustine Leudar wrote: Im sure Im missing something obvious here but humour me. With a stereo signal I can just place two speakers in a line and have my stereo signal send two discrete channels to each speakers, each channel representiong one channel of my stereo microphone. The same with quadrophonic (with no matrixing nonsense) - four mics go to four speakers placed in a square - works fine, tried it hundreds of times, no decfoding involved. Why cant you do the same for 3 dimensianal sounds ? Four mics surround sending discrete channels to four spekers placed in a square and one for height information going to a mic above your head - this should naturally represent the sound field without any decoding , Ive done this and it has been quite effective - so why the need for elaborate and expensive decoding ? Because it has advantages, see: http://en.wikipedia.org/wiki/Ambisonics#Advantages but also comes with disadvantages, see: http://en.wikipedia.org/wiki/Ambisonics#Disadvantages 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 ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Why do you need to decode ambisonic/b format signals ?
Of course this completely ignored the fact that in blind testing years ago, everyone preferred cassettes of vinyl to vinyl itself(which ought to have told people something about the recording industry's recording practices). Robert On Sun, 23 Jan 2011, dave.mal...@york.ac.uk wrote: On Jan 23 2011, Eero Aro wrote: Dave, I find a paradox in your sentence: who wants to use vinyl (or even cassette!) for aesthetic reasons Aesthetic, vinyl - yes! Agree. But cassette !!!??? What? Well, the beauty is in the eye of the beholder :-) True, so true - not something I'd choose, but. Dave ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Why do you need to decode ambisonic/b format signals ?
On 01/23/2011 03:48 PM, Eero Aro wrote: In my opinion, you can skip the on-going discussion about UHJ, it's more or less academic. UHJ was developed in the 1980's, at the time when vinyl LP and FM radio were the most important carriers. UHJ isn't needed anymore. i beg to differ. it is still very useful. for a few months now, i have done all my client's productions in HOA, even if they weren't interested in any other target format than stereo. so i mix in a way that the UHJ i deliver to them sounds great and the surround experience doesn't totally suck. which works quite well. for my own pet projects, i mix so that surround sounds great and 5.0 and UHJ folddowns don't suck. it's a really nice stepping stone for ambisonics, and surprisingly little pain to work with once you've gotten used to its quirks. and it gives you the opportunity to work with a stereo stage that's considerably wider than the speaker angle, without ad-hoc tricks. regards, jörn -- Jörn Nettingsmeier Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487 Meister für Veranstaltungstechnik (Bühne/Studio), Elektrofachkraft Audio and event engineer - Ambisonic surround recordings http://stackingdwarves.net ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Why do you need to decode ambisonic/b format signals ?
On 01/23/2011 02:53 PM, f...@kokkinizita.net wrote: On Sun, Jan 23, 2011 at 12:39:19AM +0100, Jörn Nettingsmeier wrote: http://stackingdwarves.net/public_stuff/linux_audio/tmt10/TMT2010_J%c3%b6rn_Nettingsmeier-Higher_order_Ambisonics-Slides.pdf Nice ! But I don't really agree with some of the reasoning :-) There's a logical 'jump' in there which is not explained (and it would be hard to explain it): A. In your first example (the Kirchhoff-Helmholtz Integral) the zillion mics sample the sound field on a surface surrounding the listener. This is pure WFS. B. Then you try to do the same thing with less mics, exploiting their polar patterns. But here the mics have to be coincident. not on a surface surrounding the listener. Now I don't think you can say that (B) is some form of (A) scaled down to a practical size. It is something completely different. There is no continuous way from (B) to (A) by increasing the number of channels - the mics would remain coincident and not on the surface, even in the 'infinite' limit case. true. my reasoning is that instead of sampling the sphere on every point on the surface, you use measuring microphones that look at the sphere surface from the inside. i should maybe emphasize that the size of the sphere is variable as a function of order and wavelength. The basis of (B) is not Kirchoff-Helmholtz, but Fourier-Bessel, which is the expansion of a sound field in spherical coorinates. Doing this it turns out that the angular dependency is given by the spherical harmonic functions, and the radial one by the spherical Bessel functions. in fact, i did think about tackling the problem from the fourier-bessel angle, but i haven't yet gained enough insight to really try. plus i find that the kh approach is somewhat more intuitive. and since both are ultimately converging to "perfect", i thought i might get away with it. The angular part, the spherical harmonics, can be seen as a sort of spectral transform acting on the surface of a sphere. Just as a 1-D FT maps a cyclic function (i.e. a function defined on a circle) to a discrete spectrum, the spherical harmonics represent the discrete spectrum of a function defined on the sphere (i.e. a function of direction in 3-D space). The reason why this is not a 2-D FT is because a 2-D FT has a torus [*] as its domain, not a sphere: on a torus azim and elev are independent, on a sphere they are not. So each component of an AMB signal set is really an element of the discrete spatial spectrum, not a sample of space or the sphere. true. it does not correspond to any particular point on the sphere, but it is a sample nonetheless. when explaining that to students, i often use an image analogy: when i want to transmit an image of a meadow, it's best to just paint one big green pixel first. not much, but already gives you a rough idea it's not going to be about polar bears. next, divide it into four, the upper two blue, the lower two green. then sixteen, and so on, and eventually we get the cow and the birds. point is, we will be able to make out the cow and the birds way earlier than if we had used very small pixels right from the start and displayed them left-to-right, top-to-bottom. that is hopefully similar to the discrete sampling approach of the naive KH microphone curtain vs. spherical decomposition to get a reasonably correct idea across. There is also a fundamental difference in the way a tetra mic and spherical high order mics work, and it is similar to the difference between (A) and (B). A conventional tetra mic would still work if the capsules were really coincident, it uses the polar patterns of the mics and the output signals correspond to spatial spectrum components, this is (B). An HOA mic consisting of omni capsules in free space samples the space, this is (A). Clearly the capsules must not be coincident. Its signals do not represent spatial spectrum components and have to be processed by a 'spherical harmonics transform' to provide B-format. An HOA mic with omni capsules on a solid body (e.g. Eigenmike) is a mix of the two, it's (A) at LF and (B) at HF were diffraction by the solid body makes each individual capsule directional. also true, but alas, there is only so much you can do in 20 minutes :) some things have to give. i also fully expect to roast in hell for the simplistic decoding matrices in the slides - i always add a huge bunch of caveats in my presentation, but i know at least one unlucky soul who has tried to implement them as-is. the point is: here's how it works in principle, the hairy details omitted. you can't imagine how difficult it is to sell the concept to tonmeisters - the more experienced, the harder. no point in frightening them off right from the start ;) Filippo Fazi does decoding for signals from an HOA mic in a different way: he takes the original spatial samples, and expands them using the Fourier-Bessel integral directly to speaker sig
Re: [Sursound] Why do you need to decode ambisonic/b format signals ?
True, so true - not something I'd choose, but. I'll go downstairs and wind up my HMV Gramophone from 1905, it's still working. Will my mp3 player do the same after 100 years? Eero ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Why do you need to decode ambisonic/b format signals ?
On Jan 23 2011, Eero Aro wrote: Dave, I find a paradox in your sentence: who wants to use vinyl (or even cassette!) for aesthetic reasons Aesthetic, vinyl - yes! Agree. But cassette !!!??? What? Well, the beauty is in the eye of the beholder :-) True, so true - not something I'd choose, but. Dave ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Why do you need to decode ambisonic/b format signals ?
Jörn Nettingsmeier wrote: On 01/23/2011 01:41 AM, Stefan Schreiber wrote: In fact, the introduced "system" might deliver better results than say Dolby Pro Logic IIz. that's like saying "this new car model is a lot faster than a dead whale on the beach" :-D This is a cool analogy...;-) Best, Stefan ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Why do you need to decode ambisonic/b format signals ?
Dave, I find a paradox in your sentence: who wants to use vinyl (or even cassette!) for aesthetic reasons Aesthetic, vinyl - yes! Agree. But cassette !!!??? What? Well, the beauty is in the eye of the beholder :-) Eero ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Why do you need to decode ambisonic/b format signals ?
On Jan 23 2011, dave.mal...@york.ac.uk wrote: that there are no stereo cylinder players as I'm sure someone would want that too - see http://www.bbc.co.uk/news/10171129 or better yet - http://www.touchmusic.org.uk/news/the_wire_wax_cylinders_and_evp.html - wax cylinders are clearly the wave of the future - for some value of 'future' (I've actually handled (but not played) one of those ones) Dave ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Why do you need to decode ambisonic/b format signals ?
On 23 Jan 2011, at 13:50, dave.mal...@york.ac.uk wrote: > On Jan 23 2011, Eero Aro wrote: > > >> In my opinion, you can skip the on-going discussion about UHJ, it's more or >> less academic. UHJ was developed in the 1980's, at the time when vinyl LP >> and FM radio were the most important carriers. UHJ isn't needed anymore. >> > > Unless, of course, you are a musician who wants to use vinyl (or even > cassette!) for aesthetic reasons which is what's driving my re-looking into > UHJ (ps Fons - nice analysis, very useful!). In fact, I'm only glad that > there are no stereo cylinder players as I'm sure someone would want that too > - see http://www.bbc.co.uk/news/10171129 I tend to disagree strongly. DVD-Audio, for greed of the record companies, has been a still-birth. SACD hasn't fared much better, and I will not buy any for religious reasons, because a) I won't buy a medium I can't back up, and b) it's provably an inferior and less efficient way of storing audio when compared to PCM. So that leaves for main-stream music distribution online and CDs, and the shift is going more towards on-line distribution and less to any multi-channel capable disk carrier. So for most commercially relevant music, it's the choice between lossy-compression Stereo in the form of MP3 or AAC/MP4 files, or lossless audio on a silver sliver called CD. This means, until lossles multi-channel audio is available on CD-Baby, Amazon downloads and last but not least iTunes music store; the most viable way of distributing music is UHJ encoded Stereo on a CD, just like Nimbus records did. G-Format on DVD-Video is an alternative, but it has all the disadvantages that come with a format that was meant for video rather than audio (navigation, channel bandwidth, etc.) and it works only if your speaker layout matches the 5.1 ITU setup for which it was pre-decoded. With more and more people going 7.1, 6.0, etc. the number of variations one would have to put on a disc becomes ludicrous. So we're back to B-Format, or for better or worse UHJ-stereo. Ronald ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Why do you need to decode ambisonic/b format signals ?
On Jan 23 2011, Eero Aro wrote: In my opinion, you can skip the on-going discussion about UHJ, it's more or less academic. UHJ was developed in the 1980's, at the time when vinyl LP and FM radio were the most important carriers. UHJ isn't needed anymore. Unless, of course, you are a musician who wants to use vinyl (or even cassette!) for aesthetic reasons which is what's driving my re-looking into UHJ (ps Fons - nice analysis, very useful!). In fact, I'm only glad that there are no stereo cylinder players as I'm sure someone would want that too - see http://www.bbc.co.uk/news/10171129 Dave But - you still need a decoder to decode the B-Format signals for the loudspeakers. Eero Aro ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
[Sursound] AMB Playback
On 23/01/2011 5:25 a.m., Justin Bennett wrote: Snip I have a simple 4 channel ambi decoder programmed into the built- in mixer of my computer's sound card. I just choose the preset, play the 4 channel B-format file and it decodes it for me. Would you mind giving out the details of this, or is it proprietary? Thanks, Bill ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Why do you need to decode ambisonic/b format signals ?
Augustine Leudar wrote: > Im sure Im missing something obvious here but humour me. With a stereo > signal I can just place two speakers in a line and have my stereo signal > send two discrete channels to each speakers, each channel representiong one > channel of my stereo microphone. The same with quadrophonic (with no > matrixing nonsense) - four mics go to four speakers placed in a square - > works fine, tried it hundreds of times, no decfoding involved. Why cant you > do the same for 3 dimensianal sounds ? Four mics surround sending discrete > channels to four spekers placed in a square and one for height information > going to a mic above your head - this should naturally represent the sound > field without any decoding , Ive done this and it has been quite effective > - so why the need for elaborate and expensive decoding ? Because it has advantages, see: http://en.wikipedia.org/wiki/Ambisonics#Advantages but also comes with disadvantages, see: http://en.wikipedia.org/wiki/Ambisonics#Disadvantages 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] Why do you need to decode ambisonic/b format signals ?
Anyone who would like an introduction to spherical harmonics expansions could have a look at this(which I wrote myself) http://www.regonaudio.com/SphericalHarmonics.pdf as an introduction for audio people. It is perhaps worth noting that spherical harmonics (and Fourier expansion of periodic functions) are both special cases of expansion in eigenfunctions of the Laplacian on a Riemannian manifold, a Riemannian manifold being a generalization of the idea of a surface. (I do this stuff for a living--excuse my wandering off into generality). But the article linked to is very down to earth! Robert On Sun, 23 Jan 2011, Eero Aro wrote: Gus As Fons already said, there is information available about Ambisonics. First check out these two sites: http://martin_leese.tripod.com/Ambisonic/ http://www.ambisonic.net/ In quadrophic systems the angle between adjacent speakers is 90 degrees (or more), which isn't enough to create stabile phantom images between the loudspeakers. The angle should be 60 degrees or less, especially at the sides of the listener. With quad the sound image collapses, if you move or turn your head. If you are not delivering discrete audio channels to the home listener, you need some kind of decoding anyway, such as Dolby Digital, DTS, etc. Augustine Leudar wrote: Why cant you do the same for 3 dimensianal sounds ? Four mics surround sending discrete channels to four spekers placed in a square and one for height information going to a mic above your head - this should naturally represent the sound field without any decoding , Ive done this and it has been quite effective You can. I believe that _effective_ is the correct word to describe that. With 1st order Ambisonics, you can capture (or create by mixing) a three dimensional soundfield by using four audio channels, the B-Format. B-Format is a part of a hierarchical system, which you can use for whatever playback you like, mono, stereo, horizontal surround or periphonic (3D) surround. Manipulating the three or four-channel signal is very easy and there's a lot of things you can do with it. If you use a multitude of signals for your 3D-sound, manipulating them needs a lot of processing power and tools that don't exist. There are tools for the B-Format. Using B-Format as a delivery format makes it possible, that the listener can place his speakers as he wishes. The speaker layout is defined in the decoder. The number of speakers isn't restricted to any certain number. With horizontal surround you should have at least four speakers, with 3D six speakers. It is possible to pre-decode an Ambisonic recording into a certain speaker layout. You find info about the "G-Format" in Richard Elen's article "Getting Ambisonics Around". It's in http://www.ambisonic.net/ under "Articles". With G-Format you gain the possibilities of Ambisonic recording, mixing and manipulating. What you lose, is the flexibility for the placing of the loudspeakers. In my opinion, you can skip the on-going discussion about UHJ, it's more or less academic. UHJ was developed in the 1980's, at the time when vinyl LP and FM radio were the most important carriers. UHJ isn't needed anymore. But - you still need a decoder to decode the B-Format signals for the loudspeakers. Eero Aro ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Why do you need to decode ambisonic/b format signals ?
Gus As Fons already said, there is information available about Ambisonics. First check out these two sites: http://martin_leese.tripod.com/Ambisonic/ http://www.ambisonic.net/ In quadrophic systems the angle between adjacent speakers is 90 degrees (or more), which isn't enough to create stabile phantom images between the loudspeakers. The angle should be 60 degrees or less, especially at the sides of the listener. With quad the sound image collapses, if you move or turn your head. If you are not delivering discrete audio channels to the home listener, you need some kind of decoding anyway, such as Dolby Digital, DTS, etc. Augustine Leudar wrote: Why cant you do the same for 3 dimensianal sounds ? Four mics surround sending discrete channels to four spekers placed in a square and one for height information going to a mic above your head - this should naturally represent the sound field without any decoding , Ive done this and it has been quite effective You can. I believe that _effective_ is the correct word to describe that. With 1st order Ambisonics, you can capture (or create by mixing) a three dimensional soundfield by using four audio channels, the B-Format. B-Format is a part of a hierarchical system, which you can use for whatever playback you like, mono, stereo, horizontal surround or periphonic (3D) surround. Manipulating the three or four-channel signal is very easy and there's a lot of things you can do with it. If you use a multitude of signals for your 3D-sound, manipulating them needs a lot of processing power and tools that don't exist. There are tools for the B-Format. Using B-Format as a delivery format makes it possible, that the listener can place his speakers as he wishes. The speaker layout is defined in the decoder. The number of speakers isn't restricted to any certain number. With horizontal surround you should have at least four speakers, with 3D six speakers. It is possible to pre-decode an Ambisonic recording into a certain speaker layout. You find info about the "G-Format" in Richard Elen's article "Getting Ambisonics Around". It's in http://www.ambisonic.net/ under "Articles". With G-Format you gain the possibilities of Ambisonic recording, mixing and manipulating. What you lose, is the flexibility for the placing of the loudspeakers. In my opinion, you can skip the on-going discussion about UHJ, it's more or less academic. UHJ was developed in the 1980's, at the time when vinyl LP and FM radio were the most important carriers. UHJ isn't needed anymore. But - you still need a decoder to decode the B-Format signals for the loudspeakers. Eero Aro ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Why do you need to decode ambisonic/b format signals ?
On Sun, Jan 23, 2011 at 12:39:19AM +0100, Jörn Nettingsmeier wrote: > http://stackingdwarves.net/public_stuff/linux_audio/tmt10/TMT2010_J%c3%b6rn_Nettingsmeier-Higher_order_Ambisonics-Slides.pdf Nice ! But I don't really agree with some of the reasoning :-) There's a logical 'jump' in there which is not explained (and it would be hard to explain it): A. In your first example (the Kirchhoff-Helmholtz Integral) the zillion mics sample the sound field on a surface surrounding the listener. This is pure WFS. B. Then you try to do the same thing with less mics, exploiting their polar patterns. But here the mics have to be coincident. not on a surface surrounding the listener. Now I don't think you can say that (B) is some form of (A) scaled down to a practical size. It is something completely different. There is no continuous way from (B) to (A) by increasing the number of channels - the mics would remain coincident and not on the surface, even in the 'infinite' limit case. The basis of (B) is not Kirchoff-Helmholtz, but Fourier-Bessel, which is the expansion of a sound field in spherical coorinates. Doing this it turns out that the angular dependency is given by the spherical harmonic functions, and the radial one by the spherical Bessel functions. The angular part, the spherical harmonics, can be seen as a sort of spectral transform acting on the surface of a sphere. Just as a 1-D FT maps a cyclic function (i.e. a function defined on a circle) to a discrete spectrum, the spherical harmonics represent the discrete spectrum of a function defined on the sphere (i.e. a function of direction in 3-D space). The reason why this is not a 2-D FT is because a 2-D FT has a torus [*] as its domain, not a sphere: on a torus azim and elev are independent, on a sphere they are not. So each component of an AMB signal set is really an element of the discrete spatial spectrum, not a sample of space or the sphere. There is also a fundamental difference in the way a tetra mic and spherical high order mics work, and it is similar to the difference between (A) and (B). A conventional tetra mic would still work if the capsules were really coincident, it uses the polar patterns of the mics and the output signals correspond to spatial spectrum components, this is (B). An HOA mic consisting of omni capsules in free space samples the space, this is (A). Clearly the capsules must not be coincident. Its signals do not represent spatial spectrum components and have to be processed by a 'spherical harmonics transform' to provide B-format. An HOA mic with omni capsules on a solid body (e.g. Eigenmike) is a mix of the two, it's (A) at LF and (B) at HF were diffraction by the solid body makes each individual capsule directional. An AMB decoder is in fact doing the inverse transform: from a spectral representation to speakers signals which are 'samples in space'. Filippo Fazi does decoding for signals from an HOA mic in a different way: he takes the original spatial samples, and expands them using the Fourier-Bessel integral directly to speaker signals, without ever going into the spatial spectral domain. It's a form of extra- polation in fact and clearly illustrates the potential instability (which when going to B-format instead must be handled by limiting the frequency ranges of the higher order signals). [*] Suppose you have function defined on an infinite 2-D plance, i.e. a function of x,y. You could take the 2-D FT of this, providing a spectrum. Now assume the function is cyclic in both x and y, with period 2 pi. So it consists of an infinite number of identical square tiles. Its FT is then discrete, consisting of isolated points. We take a single tile (which still contains all information) and bend it so the top and bottom ends meet, giving a cylinder. This makes the y-axis cyclic. Now we bend the cylinder so its two ends meet, making the x-axis cyclic. The result is a torus. Each point on it can be located by its original x,y values, which now can be interpreted as azimuth and elevation, both of them having a range of 2 pi and fully independent. You can't warp a square into a sphere this way, it's a fundamentally different type of surface on which azim and elev are not independent. So it's spectrum is not a 2-D FT. It turns out to be spherical harmonics. Ciao, -- FA There are three of them, and Alleline. ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
[Sursound] The 17th International Conference on Auditory Display (ICAD)-Online submissions now open
Hi everyone, Hippy New Ears! Is anyone else using ambisonics or sursound for sonification? If so, check this out [ apologies for doubles], David Call for Participation The 17th International Conference on Auditory Display (ICAD) Hotel Mercure Buda Budapest, Hungary June 20-24, 2011 URL for conference: http://icad2011.com/ URL for the community: http://www.icad.org/ ICAD is an interdisciplinary conference with relevance to researchers, practitioners, artists, and students working in the use of sound to convey information and ideas. The conference is unique in its specific focus on auditory displays and the range of interdisciplinary issues related to their use. ICAD 2011 will be a single-track conference, open to everybody, with no membership or affiliation requirements. ICAD 2011 invites the submission of new work and developments in all areas of interest to those who work with sound as a medium for conveying information and ideas. The conference emphasizes the concerns shared by those who work primarily with informational and affective aspects of sound including sonification of data and processes, synthetic and composed sound, musical sound, natural sound, and all issues related to interaction with sound, specifically, how it is presented to, and apprehended by, listeners. Thus, submissions are sought on topics that extend from basic research in auditory display, to application domains in the arts and sciences, mobile applications, accessibility, audio technology, information and communications technology, computer games, engineering analysis, medicine, and more. Each year we aim to attract a wide variety of researchers and practitioners to the ICAD community who work in fields that are concerned with and/or related to computationally based, informational uses of sound. Thus, in addition to ICAD's core interests, we hope to attract submissions from composers and artists who use sonification, acoustic synthesis, spatialization, and/or interaction techniques for composition and performance purposes. Although we fully intend to maintain ICAD's primary emphasis on the use of sound as information, we specifically want to encourage a wider and more collaborative dialogue between practitioners with disparate objectives in auditory display. This year's conference also will have an „aural submission” category for sonifications and aural compositions that employ computational auditory display techniques. It is intended that submissions in this category will be presented as part of the oral sessions. Key Dates Submission Deadline for Papers, Posters, and Aural Categories 28 February 2011 Acceptance Notification (Papers, etc.) 30 March 2011 Camera-Ready Submissions Deadline, Aural and Sonfication Contest Submissions 15 May 2011 ICAD 2011 20-24 June 2011 Theme and Topics for ICAD 2011 Topics include, but are not limited to: - 3D and Spatial Audio - Aesthetics, Philosophy, and Culture of Auditory Displays - Accessibility - Applications - Auditory Scene Design - Design Theory and Methods - Evaluation and Usability - Human Factors and Interaction - Mappings from Data to Sound - Psychology, Cognition, Perception, and Psychoacoustics - Sonification and Exploration of Data through Sound - Sound as Art - Technologies and Tools Papers Papers are oral presentations of a substantial contribution to the field. Full paper submissions should be 6-8 pages, including images and references, and should be accompanied by relevant sound files. Submissions will be subject to blind review by an international committee of peers in the auditory display community. One of the authors must present the paper at the conference for it to appear in the proceedings. Papers must not exceed 8 pages and must comply with ICAD's formatting requirements. Links to the document format templates for this year's conference in LaTeX and Microsoft Word are provided. Authors are strongly encouraged to incorporate auditory display into the presentation of their papers by including examples of the sounds used in their work and/or by sonifying their results. Just as it would be unusual for presentations of papers on graphics not to include visual artefacts, it should be the norm that ICAD paper presentations employ sound in addition to the voice of the speaker. Posters Posters are primarily a forum for discussion of work-in-progress. Submissions should be up to 5 pages, including images and references, and should be accompanied by any relevant sound files. Like papers, posters will be subject to blind review. An international panel will review submissions. Posters will be presented on a single A0 size sheet during the poster session. One of the authors must present the poster at the conference for it to appear in the proceedings. We strongly encourage everyone who is presenting a poster to consider also giving a pr
[Sursound] Why do you need to decode ambisonic/b format signals ?
Hi Gus, of course you can do what you suggest, but, speaking practically, ambisonic recording, encoding and decoding makes it possible to, for instance, go out into the field with one microphone, and record in (only) four channels. Later, depending on the situation, I can decide whether to listen in stereo, quad, with six or eight speakers or whatever I like if I use the particular decoding process. And it sounds great. Another thing, some of the decoding strategies are neither elaborate or expensive. I have a simple 4 channel ambi decoder programmed into the built- in mixer of my computer's sound card. I just choose the preset, play the 4 channel B-format file and it decodes it for me. There are also plenty of free or shareware vst and au plug ins to do the same thing. It's really not all that difficult if you ignore all the maths talk. Those guys on the list are doing that so that the rest of us don't need to ;-) (thanks guys) best wishes, Justin. From: Augustine Leudar Subject: [Sursound] Why do you need to decode ambisonic/b format signals ? Im sure Im missing something obvious here but humour me. With a stereo signal I can just place two speakers in a line and have my stereo signal send two discrete channels to each speakers, each channel representiong one channel of my stereo microphone. The same with quadrophonic (with no matrixing nonsense) - four mics go to four speakers placed in a square - works fine, tried it hundreds of times, no decfoding involved. Why cant you do the same for 3 dimensianal sounds ? Four mics surround sending discrete channels to four spekers placed in a square and one for height information going to a mic above your head - this should naturally represent the sound field without any decoding , Ive done this and it has been quite effective - so why the need for elaborate and expensive decoding ? cheers, Gus Justin Bennett j...@bmbcon.demon.nl http://this.is/justin http://this.is/bmbcon NEW RELEASES AND FREE DOWNLOADS FROM http://spore.soundscaper.com ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Why do you need to decode ambisonic/b format signals ?
On Sat, Jan 22, 2011 at 06:24:23PM -0800, Danny McCarty wrote: > >> Now this isn't too condescending is it? I certainly wasn't meant to be. From the question it was quite clear that the original poster started with zero of very little background on AMB. Taking note of this is not a reflection on his intelligence nor implying that his question was stupid. Ciao, -- FA There are three of them, and Alleline. ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Why do you need to decode ambisonic/b format signals ?
On 01/23/2011 01:41 AM, Stefan Schreiber wrote: In fact, the introduced "system" might deliver better results than say Dolby Pro Logic IIz. that's like saying "this new car model is a lot faster than a dead whale on the beach" :-D -- Jörn Nettingsmeier Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487 Meister für Veranstaltungstechnik (Bühne/Studio), Elektrofachkraft Audio and event engineer - Ambisonic surround recordings http://stackingdwarves.net ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
