On Sat, Aug 18, 2018 at 09:41:13AM +0200, Bo-Erik Sandholm wrote: > According to the document linked to below that relates self noise values to > real world applications 110 SNR cannot be related to the commonly used > reference sound level. > 110 dBA SNR would be 16 dB below absolute quiet.
Maybe possible with an unexistium membrane and left twisting electrons ... :-) > If the value 70dBA that I found for the infineon dual membrane MEMS mic is > related to 1 Pascal, then it's self noise is around 24 dB which is not > strictly studio quality. But not really horrible. It's the self noise figure which matters in the end. It simply means that if you record a sound with an SPL of say 60 dB (at the mic), the S/N ratio would be 60 - 24 = 36 dB. Using a 'pro' mic with a self noise of 10 dB the S/N ratio would be 50 dB. In both cases assuming the preamp doesn't add a significant amount of noise. Noise of 'virtual mics' (or ambisonice components) synthesised from multiple capsules is not so simple. If S_i is the signal from the i-th capsule then the beam signal is of the form S_beam = sum (a_i * S_i) i = 1..B where the a_i are complex gains depending of frequency. Now if the a_i are scaled such that the on-axis sensitivity of the beam is the same as that for a single capsule, then the noise power in the beam signal is the sum of the squares of the a_i: N_beam = sum (a_i ^ 2) For an 'omni' pattern this typically results in a significant improvement, up to 3dB * log2 (N) in the best case (ommi capsules at low and medium frequencies). For directive patterns, almost anything can happen depending on if the capsules are omni or directional, if they are in free space or on a solid body, and the order of the pattern. The actual noise will not be white which means that traditional noise figures (e.g. A-weighted) become more or less useless. Typically you may see some improvement over the single capsule noise level in some small frequency region, and more noise in other frequency bands. For some examples, get hold of the original Eigenmic manual which shows noise performance as a function of frequency for each of the available patterns. That's the only example I know of a manufacturer documenting this, most (including Zylia) will hide the truth in lots of blabla. Ciao, -- FA _______________________________________________ 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.
