For measurement purposes it should be possible to generate higher order responses using two or even one figure eight microphone. Place two figure eight microphones facing in the same direction spaced about one inch or so apart, depending on the frequency range desired. This could also be done by using a single figure eight microphone. Measure the impulse response in one direction, and then move the microphone about one inch away and measure another impulse response. Subtract the two IRs and obtain a higher order IR. This is more difficult than my simple explanation. I haven’t done this, so caveat emptor.
Eric Benjamin. From: Bo-Erik Sandholm Sent: Tuesday, April 24, 2018 8:58 AM To: sursound Subject: Re: [Sursound] RIR measuring,how to capture a higher order Ambisonic room responce? 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... 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