On Tue, Feb 23, 2010 at 04:37:53PM +0300, alex stone wrote: Jconvolver can do this, there's a config file in the distribution. This is not the recommended way to use such a reverb. The outputs from jconvolver should just go into the AMB mix bus. If you use Ardour you can connect them directly to the master bus, or you could use a 'bus' strip to have a gain control at that point. The input of jconvolver should normally come from post-fader aux sends on the same strips as where you insert the AMB panners - the panner and the aux send get the same post-fader signal. This way you can set the level of reverb for each panned source separately. The relative level of the reverb is also preserved when you use either the channel or master faders, as the reverb sits in between those, as a side chain of the master bus. In fact you can do this becaus a convolution reverb is a linear process: reverb (a) + reverb (b) = reverb (a + b). To be used like this the reverb must *not* include the direct sound. Ideally the input to the panner should also have a variable delay - to put a source at a larger distance you would then increase the send to the reverb and increase the delay in the direct sound via the panner. But this is a refinement that is difficult to arrange in Ardour, it requires using two strips for each panned source. If the reverb has many inputs corresponding to different source positions you would have as many aux busses, plus one extra for the 'tail' of the reverb which is usually a separate input for jconvolver. Ciao, -- FA O tu, che porte, correndo si ? E guerra e morte !

On Tue, Feb 23, 2010 at 09:35:42PM +0300, alex stone wrote: One for the reverb and one for the UHJ encoder. In theory you *could* combine them into a single configuration, just use separate ins/outs for each part. I wouldn't recommend doing this. Note that the UHJ encoder has a delay of 2048 samples, the price to pay for a very accurate 90 degrees phase shifter. This could be decreased, but would require a shorter Hilbert transform IR which is not provided in the current release. Ciao, -- FA O tu, che porte, correndo si ? E guerra e morte !

hi alex, fons! On 02/23/2010 02:37 PM, alex stone wrote: as fons said, jconv does a nice job of it, and i'm using it exclusively now. i did my first experiments with farina's method, described here: http://pcfarina.eng.unipr.it/Aurora/B-Format_to_UHJ.htm it's essentially the same, only that farina provides one IR per input/output pair, where fons does the same more elegantly with a single hilbert transform (they do the 90° phase shift indicated by the "j" coefficient as you find them on farina's page), and a couple of delays. the huge delay is a problem for me, because i like to A/B between UHJ and first or second order ambi - but it's easily fixed by inserting a ladspa delay plugin in the other channels. the "simple delay with cubic interpolation" works fine for me (part of the swh set iirc). the nice thing about ardour is that a mono plugin will automagically be replicated n-times in an n-channel bus. then my explanation probably sucks :( to clarify: tetraproc, a stand-alone jack application, is first and foremost an A->B converter, i.e. only useful if you have to deal with the output of a tetrahedral microphone directly. in addition, it has a virtual microphone processor that can derive any coincident stereo pair from a b-format. if you want to do just the latter, and you already have a b-format, it's easier to use the vmic plugin which is part of fons' AMB plugins - it does the same job, but is simpler to use (no jack patching). if you have a b-format and want to produce stereo, these are the two options you have: 1. use UHJ to fold it down automatically (including extra surround information that allows the consumer to blow it up to horizontal surround again, with a few compromises). but since uhj basically moves the rear sound stage to the front, it can sound slightly over-ambient (not as extreme as blumlein stereo, though). 2. use a virtual stereo mike to pick out a stereo perspective. it allows for more control, is a lot easier to produce, and it's probably the safer option if you want your mix to be reliable on consumer gear... i'm experimenting with uhj, but i've found that the sound stage can vary wildly between different playback systems. it's superior to my ears when all goes well, but difficult to control. and "controlling" here means to tweak your surround mix and anticipate what it will do to the UHJ. weird way of working. if on the other hand you never listen in surround and only mix for UHJ, the b-format will likely not make much sense when played back ambisonically. :) same here. i may have two years of a head-start, but fons has endured extremely dumb questions on the way... so i'm happy to be of assistance to others now! there is no ladspa UHJ encoder yet. i would definitely go that way, to be able to easily provide a b-format output. since you are dealing with artificial sources anyways, why stick to first order? do your panning in higher order instead. the use of resources is minimal (although it will create an insane amount of jack ports, so use -P2048). it won't make any difference to your UHJ, since it only ever sees WXY, but it would enable you to produce really crisp n.1 or HOA decodes without any extra work. just one, totally unrelated, but smart(-ass) nonetheless: could you please edit your replies to quote only the part you are directly referring to? i'm usually very curious about things you have to say on the list, but my mouse wheel finger is getting RSI... best, jörn

2010/2/24 Jörn Nettingsmeier <nettings(a)folkwang-hochschule.de>de>: I'm on the Hilbert as of last night. Makes a challenging job simpler, i'd agree. > if you want to do just the latter, and you already have a b-format, it's > easier to use the vmic plugin which is part of fons' AMB plugins - it > does the same job, but is simpler to use (no jack patching). > if you have a b-format and want to produce stereo, these are the two > options you have: > 1. use UHJ to fold it down automatically (including extra surround > information that allows the consumer to blow it up to horizontal > surround again, with a few compromises). but since uhj basically moves > the rear sound stage to the front, it can sound slightly over-ambient > (not as extreme as blumlein stereo, though). > 2. use a virtual stereo mike to pick out a stereo perspective. it allows > for more control, is a lot easier to produce, and it's probably the > safer option if you want your mix to be reliable on consumer gear... 1.) I've had the ambient overdone already, so i understand what you're saying here. 2.) Virtual stereo mike? I don't understand this bit. Do we have one in Linux? Or are you referring to a process i have to build up myself? >> The intent with this is provide ambisonic positioning, and convolver >> tail, right up until downsizing to stereo as the last part of the >> signal chain. > i would definitely go that way, to be able to easily provide a b-format > output. Sounds like a plan. > since you are dealing with artificial sources anyways, why stick to > first order? do your panning in higher order instead. the use of > resources is minimal (although it will create an insane amount of jack > ports, so use -P2048). it won't make any difference to your UHJ, since > it only ever sees WXY, but it would enable you to produce really crisp > n.1 or HOA decodes without any extra work. I don't know enough about higher order yet, but i am proficient in handling insane amounts of of ports, so that bit isn't overwhelming. :) > just one, totally unrelated, but smart(-ass) nonetheless: could you > please edit your replies to quote only the part you are directly > referring to? i'm usually very curious about things you have to say on > the list, but my mouse wheel finger is getting RSI... > best, > jörn Good point, and i'll endeavour to do this in future. My thanks to you and Fons for the info, and your continued generosity in sharing. Alex. -- www.openoctave.org midi-subscribe(a)openoctave.org development-subscribe(a)openoctave.org

Jorn, Fons, I'm getting deeper into a setup now, and trialling a few different configs. A further question. Given that an amb sphere is equal on all "sides", and the sweet spot is the centre (roughly speaking), should i be configuring my dry sound orchestral instruments/sections to use the upper-rear/rear quadrant of the sphere, assuming the centre is the listener, in a total space? In a real world setup, my orchestra is on the stage, and the listener may well be (at my choice) sitting in a spot equidistant from the back/front/left/right of the total space. Should i assume this as a point of reference to begin with? My "speakers" will be not only on stage, but as ambient sound/reflections in the rest of the space as well. The space isn't exactly spherical. Alex. -- www.openoctave.org midi-subscribe(a)openoctave.org development-subscribe(a)openoctave.org

On Wed, Feb 24, 2010 at 5:29 PM, <fons(a)kokkinizita.net> wrote: Aah, now i'm clearer on the perspective. Thanks Fons. I found the amb plugin for the stereo mike as well. -- www.openoctave.org midi-subscribe(a)openoctave.org development-subscribe(a)openoctave.org

On 02/24/2010 03:29 PM, fons(a)kokkinizita.net wrote: there is no "back/front/left/right of total space" you could be equidistant from - ambisonics is not concerned with walls at all, just with directions. sources can be as close or as far away as you want, but the panner won't do that for you - you have to create the illusion manually, with delay, eq treble rolloff to simulate air-damping, and more reverb (unless you're mixing an outside scene). in theory, HOA could do distance coding, but i don't know how to do that, yet. fons might be able to point to some information, but i doubt it would be worth the trouble at this point, as it's mostly about proximity effect anyways (i.e. bass boost for close sources)... your "point of reference" is your listening position. it's the origin of your coordinate system (see farina's page for an illustration of the axes). 0° azimuth is to the front, positive angles are to the right (mathematicians have it the other way round, but the AMB panners do it so that the motion of the slider will correspond to the motion of a source). 0° elevation is on the horizonal plane, 90° is the zenith (right above your head), -90° is the nadir (watch for bum diffraction :-D) ah, you want to fake wall reflections. tricky. you would want a room synthesizer for that... how are you generating those reflections?

Thanks fellas. great information. Alex. -- www.openoctave.org midi-subscribe(a)openoctave.org development-subscribe(a)openoctave.org