Thank you all, for your answers. I received a lot of information. I will start with FOA RIRs from my tetramic , it seems my ideas for measuring higher orders are not realistic without a higher order microphone.
And FOA is probably good enough for my proof of concept. Best Regards Bo-Erik Sandholm Stockholm On Tue, 24 Apr 2018 03:59 umashankar manthravadi, <umasha...@hotmail.com> wrote: > I have been using a stepper motor (of the kind used in 3d printer ) driven > by a low cost Arduino and motor control board. I 3d print a snug fitting > fixture for the microphone with the motor shaft aligned to the array > centre. It is low cost so I design a fitting for each mic I test, including > the Brahma-in-Zoom. A small Arduino script rotates the stepper 25 steps > each time I press a button (for 16 positions) and 50 steps (for 8 > positions). I was worried about the stepper skipping with the weight of the > microphone, but that is not happening, even with a five volt supply. I was > ready with a thrust bearing between the motor housing and the microphone > housing but it was not necessary. I plan to get rid of the switch and use a > pulse on the right channel instead, though I generally do not like to > automate things too much. > > > > umashankar > > > > Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for > Windows 10 > > > > ________________________________ > From: Sursound <sursound-boun...@music.vt.edu> on behalf of Fernando > Lopez-Lezcano <na...@ccrma.stanford.edu> > Sent: Tuesday, April 24, 2018 1:40:56 AM > To: Surround Sound discussion group > Subject: Re: [Sursound] RIR measuring, how to capture a higher order > Ambisonic room responce? > > On 04/23/2018 12:42 PM, Stefan Schreiber wrote: > >> I can do the 4 measurements with 45 degrees rotation of my tetramic, > that > >> is not so difficult, the next step to create a second order ambisonic > >> RIR > >> > >> that is where I will fail :-). > > You would need to "calibrate" the created 8 capsule array. That is, > record impulse responses all around it in a big space or anechoic room > (enough to accurately sample the spherical harmonics you want), and then > derive an A to B converter from that. I have some preliminary code in my > SpHEAR project that tries to do that, but it is not a "push a button and > you are done" thing at all... > > For Fons's code, and to do this the "right way"... > On 03/27/2018 01:18 PM, Fons Adriaensen wrote: > > ... you'll have to sell your soul :-) > > :-P > > > I believe you might need a quite high precision to be successful even at > > the first step... > > > > (A SF mike has narrowly spaced capsules, and needs calibration....The > > mechanical precision you need to measure 2nd order with a FOA mike is > > IMHO high.) > > Based on my experience with the Octathingy's I have built I would agree, > you would need to be very precise (and repeatable). > > In my case to get good calibration data I need to rotate the microphone > with no wobble and at different orientations (or if it is not _exactly_ > perfect, try to get away with calibrating out the average delays to all > capsules). > > BTW, I cannot move the speaker around which would probably be a better > solution because of space constraints... I can barely get 4.5mSecs of IR > data in the spaces I can use. > > > So the mathematical methods (based on FOA but improving the RIR > > resolution, as suggested by Archontis) should be a better way to go > > on... Especially since you could receive even higher resolutions/orders, > > and in practice. > > > > So the presented ideas to capture 2nd order RIRs via a 1st order mike > > are brilliant, but are they practical? > > Probably not practical IMHO. > > > And even if somebody could succeed in a very careful process: this does > > not look to be a robust measurement method. .. > > > > We always talk about the 1st reflections, in this case. Not reverb, > > which is kind of statistical. > > > > Of course you can try, but how much precision is really needed? (Should > > be clarified before...) > > I would have to go to my data to get some numbers... I definitely can > see effects at high frequencies when the data capture is not precise > (I'm in the process of trying to build a better measuring rig). > > -- Fernando > > _______________________________________________ > Sursound mailing list > Sursound@music.vt.edu > > https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fmail.music.vt.edu%2Fmailman%2Flistinfo%2Fsursound&data=02%7C01%7C%7Cd2d37994bf824a649cfd08d5a9565d6f%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636601110750131368&sdata=9yJTw53ccb0AvWlk1eg1qrtsvsUW7PeBngbvZ3w9Hck%3D&reserved=0 > - 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/20180424/5f8768e9/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. > -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://mail.music.vt.edu/mailman/private/sursound/attachments/20180424/8d01b22f/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.
