Digital microphone

Paper on theory of a Digital microphone.

"A basic concept of direct converting digital microphone
An electroacoustic system which directly converts analog acoustic signals to digital electric signals is described. The system consists of a subtractor, a sampling and holding circuit, a sigma?delta modulator as a comparator, an accumulator, and a local direct digital-to-analog converting transducer similar to a typical electronic analog-to-digital converter. The subtractor is an electrostatic device which has a diaphragm, driving electrodes, and a detecting electrode. The surface area of the driving electrodes corresponds to the significant bits in the digital signal, as an electroacoustic digital-to-analog converter. The detecting electrode produces an electrical signal proportional to the displacement of the diaphragm driven by subtracting the received acoustic signal from the electrostatically driven force. This is regarded as a subtractor. The detected signal is amplified and sampled-held and modulated by the sigma?delta procedure and generates a signal of +/-1 bit, which is added to the accumulator memory by a high clock frequency. The output of the accumulator is the digital signal output and is also fed to the driving electrodes. A 4-bit conceptual system was developed to affirm this concept. © 1999 Acoustical Society of America."

Hi PRR,

The link leads to a "Subscriber only" message.


Any chance of converting the article to PDF and posting it?


Thanx...


Rogy

Does this theory do away with the need for a mic pre? If so you could look at it as a compromise as well as an advantage. I am a firm believer that musical tones are produced by a mic and preamp working in harmony. I see the relationship as somewhat like a camera and a lens. Both contribute to the final product, imparting their own characteristisc on the final product.

Shane

> The link leads to a "Subscriber only" message.

I was shocked to see it, since AES is in the business of selling these things. But I got to it right through Google, without any AES credentials in my browser.

I've changed the link to the Abstract page, which probably is supposed to be Public. I tried that in another browser: the Full Text link opens the article. It probably is not supposed to....

> Any chance of converting the article to PDF and posting it?

No way.

No conversion is needed (it is already PDF), but clearly AES wants to sell this. I'm not going to host it. I think it is a server-bug that left it "out in the open" for me to see. Since I know you guys would rather die than buy an article, I'm not "costing" AES anything. But maybe a flurry of hits on an obscure paper will get their attention and get this loophole fixed.

> musical tones are produced by a mic and preamp working in harmony.

Musical tones are produced by musicians.

While the recording engineer is sometimes part of the band, in many cases the recording engineer should NOT "add anything", simply capture the air waves as exactly as possible.

As far as I can tell, this mike significantly reduces diaphragm action, and reduces the preamp to a comparator. If the diaphragm moves at all, push it back. The push-back signal is the audio output, and in this case is already in digital format.

FWIW, I remembed having read something about (more or less) digital mics not that long ago. Here it is:

http://www.soundonsound.com/sos/mar04/articles/cuttingedge.htm?session=26f984a1df84852139d027abbbb49d84

Peter

[quote author="PRR"]

While the recording engineer is sometimes part of the band, in many cases the recording engineer should NOT "add anything", simply capture the air waves as exactly as possible.
[/quote]

Tell that to my clients.

LMAO :thumb:

If i captured what came outta them and never added/enhanced anything, i'd never work in popular music again.

But i doubt this microphone idea is aimed at popular music. probably headed for the jazz/classical purist market. Where it'll definitely sell...

[quote author="Category 5"]Does this theory do away with the need for a mic pre? [/quote]
No, it uses comparator in sigmadelta modulator
as "mic pre"
This serves as low noise preamp with small dynamic ratio.

Some guys at my school works on it.

But what about mic function? Normal mic is condenser with
constant charge. But this mic is threeport. One port is acoustic,
two ports are electric.
Sensing electric port is constant Q,
actuating port is constant V. Something inconsistent ?
actuating port is variable negative compliancy?
Yes, but feedback destroy this irregularities.
With infinity feedback there is no membrane motion and
only variations on V (=F)
(in pressure, normally compliance controlled mic)
Membrane properties are insignificant for
transfer and pressure is
directly transformed to force.

But in feedback systems we must pay increased transfer by worse
noise characteristics. I never seen this type of digital mic
performs. I see this only as laboratory kit an many
peoples around it and it is still oscillating ... .

xvlk

BTW, didn't Neumann try this with the Solution D or something like that? It sold, what, two or three units? IMHO they should concentrate on keeping the rest of their product line from sinking any firther...

[quote author="JPrisus"] didn't Neumann try this with the Solution D or something like that? .[/quote]
No, Solution D (or D01) is normal mic (condenser, constant
charge) with nice gain-staged amp.
Some patents (Otmar Kern) are couplet with it.
This is followed by two ADC in the mic body.
xvlk

> didn't Neumann try this

A truly digital mike (not just an analog mike with an ADC in the body) is, today, pretty much what xvlk says:

> laboratory kit and many people around it and it is still oscillating....

(However, it does keep the university research assistants busy and out of trouble.....)

If you read the paper, the demo was a 4-bit microphone. For general recording, we need 20 bits. We have a LONG way to go. The way they sliced the 4-bit backplate is easy but wrong (Bell Labs did 6 concentric bits decades ago). Making a 20-bit comparator is probably 64,000 times harder than a 4-bit comparator.

No, this is future-think. You won't see a commercial product soon.