I did this rotation and calibration operation. Unfortunately the results were not great. When the array is rotated it has to overlay the previous position perfectly. There is also a tendency for the mic stand to wobble when it rotates. These results are shown in my AES paper on the second order microphone.
Eric Benjamin From: Fernando Lopez-Lezcano Sent: Monday, April 23, 2018 1:11 PM 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://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/20180423/d0ecb05b/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.
