Hello and a happy new year to the list, just to mention some more resources on this topic: part of the open-source Matlab libraries I made public last year deals with this matter: deriving the matrix of filters form the microphone to the B-format signals, FOA or HOA.
The filters can be computed from a description of the array (e.g. 6 super-cardioids at some desired radius and with desired orientation, or 16 omnis on a hard sphere), or from a set of anechoic measured responses of the array. The solution can be chosen from a few different published approaches, based either on a regularized LMS (similar to Farina’s solution) or a thresholding inversion approach. There is not extensive documentation at the moment, one needs to study the functions a bit, but you can see the results in action for the Eigenmike in these demos, along with the code that produces them: http://research.spa.aalto.fi/projects/spharrayproc-lib/spharrayproc.html#3 where the filters are computed and evaluated based on a “theoretical” perfect Eigenmike, and then based on actual Eigenmike measurements. The evaluation is based on spatial correlation of the filtered responses, showing how similar the directivity shape across frequency is to the ideal one, (e.g. how closely the X channel resembles the perfect dipole), and level difference between the actual and the ideal component, taken as the RMS across all directions (diffuse level). A report on these may follow soon - in the meantime if somebody’s interested to use these, let me know for additional help. Regards, Archontis On 06 Jan 2017, at 03:54, David McGriffy <da...@mcgriffy.com<mailto:da...@mcgriffy.com>> wrote: I recently developed a MatLab script to create calibrations based on Angelo's method. Set up equations for each measurement's expected results, find the LMS solution in each frequency bin, then build the resulting filter matrix. A little engineering around the low and high frequencies and it seems to work pretty well. I'd also like to point out that VVEncode (alas not VVTetraVST or VVMic) will process anyone's 4x4 matrix of filters if they are put in wav files like Angelo and Brahma do. I also have matrix calibration processing in my command line tool and I've done it in pure MatLab. Contact me if you want to try this and have any questions. I mention all this mostly because I'd be interesting in processing anyone's custom measurements. For me this is test data for my scripts. So far I've only run data out of one lab and with one type of excitation/reference/etc. I'd like to make sure I'm not dependent on those things. And I can return a working calibration, I hope. David VVAudio On Thu, Jan 5, 2017 at 1:21 PM, Fernando Lopez-Lezcano < na...@ccrma.stanford.edu<mailto:na...@ccrma.stanford.edu>> wrote: On 01/05/2017 02:19 AM, umashankar manthravadi wrote: Indeed. I have an (if memory serves) emm6 "reference microphone" which is not very expensive but comes with its own calibration curve. Flatness is important as that will define how true is the frequency response of the calibration. For the excitation I use a single driver small speaker, so far it has been fine. I record is our rather small concert hall (the Stage) and I managed to get about 5 mSecs of useful data before the first reflection arrives. That seems to be enough. Completely agree with sealing the bass port if you have one like that, that's what Eric Benjamin recommended doing. I'll probably be offline for a few days, sorry (vacation, no internet, bliss)... Good luck! -- Fernando Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Windows 10 From: Bo-Erik Sandholm<mailto:bosses...@gmail.com> Sent: Thursday, January 5, 2017 3:31 PM To: sursound<mailto:sursound@music.vt.edu> Subject: Re: [Sursound] [allowed] brahma To get a good calibration, I expect I will need at least one known/reference source or sensor? The reference for me will probably be my coresound Tetramic. I will probably use Kef eggs as speakers as they are coaxial transducers. Only at low frequency will The port be offerter. Have I understood The basics? I will probably measure outside a calibration Day orborrow a anechoic room at swedish radio. Bo-Erik Den 5 jan. 2017 11:53 fm skrev "umashankar manthravadi" < umasha...@hotmail.com<mailto:umasha...@hotmail.com>>: Dear fernando I forwarded your link to marc Lavallée when you first posted them. My intent is that we should have multiple compatible systems for calibrating A format mics Sent from my Windows 10 phone From: Fernando Lopez-Lezcano<mailto:na...@ccrma.stanford.edu> Sent: 05 January 2017 00:28 To: Surround Sound discussion group<mailto:sursound@music.vt.edu>; glard...@iol.ie<mailto:glard...@iol.ie><mailto:glard...@iol.ie> Subject: Re: [Sursound] [allowed] brahma On 01/02/2017 09:59 PM, Bo-Erik Sandholm wrote: Good luck in your continued effekt. By the way, i have accuired one of your Tetra mic 3d shapeway for 14 mm capsules. I have not yet assembler it. I Wonder is there any software package and description on How to create calibration files for The mic? I will probably have The possibility to get temporary access to a anechoic room. Hi Bo-Erik, You could take a look at my project here (I posted about this a while back): https://cm-gitlab.stanford.edu/ambisonics/SpHEAR/ (there is mailing list with 0 posts so far, ha ha..) See paper here (been working on this for over a year): https://ccrma.stanford.edu/~nando/publications/sphear.pdf The project includes free software (open source, GPL) that runs in Matlab and derives a calibration matrix (4x4 matrix of FIR filters) that can be used directly with TetraProc (by Fons Adriansen) - or any other software that can run the filters. Just a few days ago I _finally_ managed to get the software into somewhat usable shape in that I think (and I'm pretty much wrong every time I say this, so...) it is working correctly. The calibration relies on having 16 measurements (could be 8) in the horizontal plane around the Ambisonics microphone plus one more of a calibration microphone in the same exact location. Aliki is used to capture the IRs and edit (trim and window) them. DRC (Digital Room Correction) is used to equalize the excitation speaker. Then the software I wrote processes those IRs and outputs a 4x4 matrix of filters. Many parameters can be tuned. I'll post a couple of pictures later... Documentation (surprise!) is mostly lacking. I hope to remedy that somewhat soon (at least a list of the sequence of octave function calls you need to get the job done). My latest prototype with 10mm capsules was hastily measured before I left for "vacation" and the plotted results of the calibration are looking good. A re-calibration with the latest software of my first prototype which captured a full concert also sounds fairly decent. Anyway, Good luck! -- Fernando In worst case i Will use the generic calibration from sennheiser :-) The mechanical size of The tetraeder is about right. Bo-Erik Den 2 jan. 2017 9:01 em skrev "Gerard Lardner" <glard...@iol.ie>: Sorry to hear of the falling-out. I have had some issues with the build-quality of my Brahma, which was made by Embrace Video, but nevertheless it remains my 'go-to' mic for choral recording. With best wishes for 2017, and for your ongoing Ambisonic microphone projects, Gerard On 02/01/2017 06:57, umashankar manthravadi wrote: This is just an announcement that Nakul Sood and Embrace video will no longer be manufacturing or selling Brahma ambisonic microphones. Our very informal arrangement has come to an end as Nakul Sood demanded 1)I hand over complete technology and manufacturing protocols, 2) sign a non-disclosure agreement and 3) sign a non-compete agreement. (there were other demands) I have always worked on Brahma as a shared project, with help from many people and I have no desire to sign a non-disclosure agreement. I had made atleast 20 Brahma microphones before this project began, and I will continue to make one off brahmas as demanded (I am currently making five second order microphones for Angelo Farina) and I am setting up fairly high tech processes in Bangalore where I now live (laser cut microphone bodies!) Umashankar -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://mail.music.vt.edu/mailman/private/sursound/attachme nts/20170102/572ce57e/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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