Microphones in parallel to reduce noise
in [Design]
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From: miso on 16 Dec 2009 22:15 On Dec 16, 4:09 pm, o...(a)uakron.edu wrote: > Ok, each mic has a surface mount network around it for frequency > shaping. and each one has a internal fet. Until I can dig into it in > the morning I don't know the values, 805 parts that I cant see until I > get a microscope. A bit of probing reveals the outer ones are > tailored to low freqs, inner ones to highs, and gain increases towards > the centers of the array. > > Steve Not exactly frequency shaping, but probably time delay via networks. You need delay to do beam forming. It is easier in radar since the bandwidth is narrow. For audio, you are much better off using DSP techniques where delay comes for free in the sampling. I looked into doing a product with multiple microphones years ago. The idea was not to do beam forming, which merely steers the signal, but zone forming. It is possible with DSP to narrow the pickup to a zone rather than have the beam go out to infinity. The problem with beam forming is it is a patent mine field. As you probably know, half the patents litigated are proven to be invalid, but the cost to litigate makes developing the project unfeasible for the small investor. Even a large Japanese firm I was dealing with didn't want to do it. It would be interesting to see how Polycom got their project to market.
From: miso on 16 Dec 2009 22:20 > > How many Gigaohms input impedance will the complex chip have ? > > Graham The issue is more related to ESD protection on the chip. You can make a very high impedance amplifier in CMOS, but it would be a touchy product in assembly. I don't recall running into a BICMOS with JFETs, but that would be a better technology.
From: Michael A. Terrell on 16 Dec 2009 22:37 krw wrote: > > On Thu, 17 Dec 2009 11:29:21 +1100, "Phil Allison" <phil_a(a)tpg.com.au> > wrote: > > > > >"krw" > >> > >> Some "dynamics" are really electrets in drag. > > > > > >** Totally stupid bullshit. > > > In fact, you are. You and DimBulb; a perfect pair. Just don't try to seperate them. You know what happens when you try to divide zero by zero. -- Offworld checks no longer accepted!
From: osr on 16 Dec 2009 22:44 On Dec 16, 9:23 pm, Eeyore <rabbitsfriendsandrelati...(a)removethishotmail.com> wrote: > o...(a)uakron.edu wrote: > > AMBIENT ** noise pickup, not self noise !! > >> In any case, YOU are 100% WRONG in your assumption that there ought to > >> be a noise problem when combining the mics signals. Wired either in series > >> or parallel, correlation still works to improve the s/n ratio. > > > Mixer front ends still add thermal noise > > Uh ? What's a 'mixer front end' ? Obviously you're not an audio > professional and haven't a clue about current practice. You can make a > mix stage today using inexpensive off the shelf parts that has 100dB or > more dynamic range quite easily. > > So what's the mix stage chip ? > > Graham Nope, My experience is with 1980s audio when every open channel was a problem. I'm glad to admit that. I'm a laser/electro-optics guy. Any specfic AES paper? Steve
From: George Herold on 16 Dec 2009 22:46
o...(a)uakron.edu wrote: > My boss laid a unit on my desk today. Its got ten electret mics fed > into one low noise opamp. Any ideas how they did this without a ton > of noise. All I can see from the board layout is it is NOT the classic > op amp summer. > > Any suggestions for papers on low noise signal combining? > > Steve Crazy idea, Is there anyway to add them in series? George H. |