zyla is made of mems. We are now getting low noise and high sensitivity mems, but they are still omni.
Omni mounted on the surface of a sphere has some directional characteristics. Later today I am going to measure a single mems loaded with a 16 mm square horn (mouth flush on a 40 mm sphere) to see what kind of directivity pattern I will get. umashankar ________________________________ From: Sursound <sursound-boun...@music.vt.edu> on behalf of Fernando Lopez-Lezcano <na...@ccrma.stanford.edu> Sent: Friday, August 17, 2018 12:05 AM To: Surround Sound discussion group; Len Moskowitz Cc: Justin Bennett Subject: Re: [Sursound] Looking for mic advice (Zylia) On 08/16/2018 10:22 AM, Bo-Erik Sandholm wrote: > I agree with Len, we have not seen any technical spec of self noise level > of the MEMS (clusters?) that are used in Zylia. > > Only text saying that in normal musical recording situations self noise is > not disturbing :-). :-) > I have a personal theory that self noise of physical elements in an > ambisonic mic array is not directly additive. > The basis for my theory is that as we convert to B-format the noise from > all the physical elements are distributed over a spherical surface, > and the noise level for a virtual microphone in decoding do not have the > full sum of the added microphone noise levels. > Only coherent noise within the take up volume of the virtual microphone is > relevant in that directional microphones response. I think the noise we are talking about is that of the difference microphones. In an open array built with cardioids that would be for order 2 or higher, in a rigid sphere array with omnidirectional capsules that would be for order 1 or higher. Those components drop in level at low frequencies at a rate of n x 6dB/octave (starting at high frequencies). For the second order components of a microphone made of cardioids n = 1 (6dB/oct), add 6dB/oct per order increase for higher orders. As the component drops in amplitude towards the low frequencies you need a filter that compensates for the drop, and of course it amplifies the sef-noise of the capsules as well. At some point you have to give up or the noise becomes a problem (where exactly depends on the self-noise of the capsules and what kind of materials you are recording). In the second order microphones I'm building for the SpHEAR project I can use the second order components down to about 400-500Hz ("unity gain" for them is at around 9KHz). Even then the noise is objectionable (but not necessarily "disturbing" :-) for recordings that have wide dynamic range (my encoder uses an expander on those components to try to minimize that effect). You can definitely hear the noise if there is a silence in the recording. Of course it disappears if you mute the second order components :-) A third order microphone (made of cardioids - I don't think there is one) would be worse, the drop would be 12dB/oct for the third order components. So you would have to limit the low end of the frequency response at a higher frequency. AFAIK nobody specifies the noise specs for _those_ components in an Ambisonics microphone. In a first order microphone made of cardioids that is not a problem, as is the case for the first order components of a second order microphone made of cardioids. (as a reference, the open source octofile software released for the OctoMic shows that their calibration has three choices for the low frequency cut off for the second order components, 500Hz, 900Hz and 1.5KHz). -- Fernando _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fmail.music.vt.edu%2Fmailman%2Flistinfo%2Fsursound&data=02%7C01%7C%7C880a958762324ad22ac808d603a71cca%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636700413605498803&sdata=XyLmjx2mOOdApTO%2FBIrFR0Mzo%2FYnFvCW4Pes6Do7U3w%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/20180817/2db3da37/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.