I never achieved satisfactory (electronically quiet) environmental recordings with the portable Soundfield. Maybe the ones I used weren't properly calibrated: they were certainly affected by humidity. I have had much better luck with the TetraMic - as long as radio interference can be kept under control. Garth: what cable lengths are you using and are the inputs balanced?
D. On 07/08/2014, at 1:03 AM, Eric Benjamin wrote: > Garth, > > I wonder why it is that your recordings are so afflicted by noise. The self > noise spec for the SPS200 is 12 dBA, which is similar to that of other > soundfield microphones from Soundfield. While 12 dBA isn't noise free, it > should be pretty quiet. As a reference, the average threshold of > detectability for microphone noise is about 6 dBA, assuming a natural > recording scenario. That is, assuming that the sounds are replayed at the > same level at which they occurred in the recording environment. > > Of course, it may be that the microphone doesn't meet specifications. > > I'm a bit confused by the recordings that you placed at > http://listen.ame.asu.edu/sonic_events.php > > > The first recording is labeled as "no audio". The second recording is > labeled as "you can hear Garth open his canteen and move some things around." > There's certainly a lot more noise in that second recording. About 46 dB > more, unweighted. It would be interesting to try to perform some more > controlled recordings to find out whether the noise is coming from the mic, > or not, and whether it meets specifications. > > Do you ever get to the SF bay area? > > Eric Benjamin > > > On Wednesday, August 6, 2014 3:12 PM, Sampo Syreeni <de...@iki.fi> wrote: > > > > On 2014-08-06, Joseph Anderson wrote: > >> I take the noise profile from each individual A-format channel... > > At the risk of sounding trite, what is noise? I'd argue that it isn't > one thing, and that it's pretty difficult to define with mathematical > precision. If you're talking about environmental background, then > approaches like gating A-format or some other suitable directional > representation of sound is a good idea. > > If you're talking about tape noise instead, that isn't directional at > all, at least until you get into directional masking calculations over > what you can throw away without getting caught. In that case you'd want > to operationalise what you consider noise, then find out an optimal way > of extending that idea to B-format, and do the kind of joint processing > Eero suggests. > > The easiest way probably is to go with just W in the sidechain and equal > gating for all the channels in the main one. The next step would be to > do the same per frequency, and so on. However, in the ambisonic world, > you'll then bump into a third source: the mic. Since the Soundfield > works on differencing principles, W has a totally different noise > profile from XYZ, and typically it only gets worse from there as the > order goes up. (Or it doesn't; that depends wholly on the mic geometry.) > > The point is, I don't think there is a monolithic thing called "noise" > which can be just blindly "reduced". There never was even in monophonic > recordings, and the free degrees of freedom in your signal chain just > multiply when you go through stereo to ambisonic. So, you need to be > careful about which source(s) of unwanted hiss, distortion or bogus > sources you're talking about, you'll have to develop computationally > tractable models of both your utility signal and the noise, and only > then can you really start to combine all of the machinery into something > which actually works/sounds good. > > E.g. when you expand/limit A-format, implicitly your noise model is a > hiss which is directional to first order and your model of the utility > signal is something like a strong, wideband directional signal near it, > which makes directional sine-to-noise masking statistics relevant. Break > those conditions and bad things will most likely happen. > > So, try your approach on a two sine test signal, separated in frequency > more than a critical band's worth. Pan one of the sines due front, and > revolve the other one around at about 1Hz and say -6dB. Then add pink > noise at about -10dB to each of the B-format channels independently. I'm > rather sure that while your approach will work beautifully for the front > signal alone when adjusted right, it'll lead to nasty, anisotropic noise > pumping with the dynamic signal in place. > > (Oh, and by the way, which A-format? As long as you're dealing with a > perfect mic and linear, time-invariant filtering operation, you don't > have to think about that because you can go willy nilly between A and B. > But once you start applying this kind of processing, every possible > orientation of the mic gives rise to a separate A-format. Which one > should it be? The above example presumes one of the capsules is facing > towards the reference. It gets much worse if you place the source > directly between three adjacent capsules, in angle space.) > -- > Sampo Syreeni, aka decoy - de...@iki.fi, http://decoy.iki.fi/front > +358-40-3255353, 025E D175 ABE5 027C 9494 EEB0 E090 8BA9 0509 85C2 > > _______________________________________________ > 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/20140806/e445ee8b/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. ______________________________________ Prof. Dr. David Worrall Emerging Audio Research (EAR) Audio Department International Audio Laboratories Erlangen Fraunhofer-Institut für Integrierte Schaltungen IIS Am Wolfsmantel 33 91058 Erlangen Telefon +49 (0) 91 31 / 7 76-62 77 Fax +49 (0) 91 31 / 7 76-20 99 E-Mail: david.worr...@iis.fraunhofer.de Internet: www.iis.fraunhofer.de Senior Adjunct Research Fellow, Australian National University. david.worr...@anu.edu.au -------------- next part -------------- An HTML attachment was scrubbed... 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