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Old 29th October 2012, 05:06 AM   #28611
1audio is offline 1audio  United States
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Originally Posted by RNMarsh View Post
????? What?
I could have sworn I mentioned CM relates to THD production.... especially in asymmetrical topologies, in particular. And, that tests using asym waveforms have a CM component to them to deal with. Thus, whats the CMR... doesnt anyone care about this aspect of amp design. You should. Thx-RNM
Actually common mode issues are basic to non-inverting amplifiers. In a non-inverting amp both if the differential inputs are moving with the input signal, the feedback terminal following the input as closely as possible. Inverting amps do not have this issue and tend to have less distortion for that reason. Asymmetry of the waveform has little to do with this issue.
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Old 29th October 2012, 10:10 AM   #28612
RNMarsh is offline RNMarsh  United States
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Originally Posted by morinix View Post
Those are for industrial applications. I was wondering because couldn't recall seeing a review in the recording magazines.
The microphone is not for any one appl. These are low distortion, wide bandwith mics.... not any less suitable than "measurement" mics cannot be used for recording music. Try them and learn. -RNM
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Old 29th October 2012, 10:14 AM   #28613
RNMarsh is offline RNMarsh  United States
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Originally Posted by 1audio View Post
Actually common mode issues are basic to non-inverting amplifiers. In a non-inverting amp both if the differential inputs are moving with the input signal, the feedback terminal following the input as closely as possible. Inverting amps do not have this issue and tend to have less distortion for that reason. Asymmetry of the waveform has little to do with this issue.
Asym has everything to do with CM signal source to be dealt with. CM signals do no Only come from rfi/emi/60Hz pickup/grounding. Other issue is how does amp do with CM signals -- CMR? Need to test it or SIM it. Thx-RNM

Last edited by RNMarsh; 29th October 2012 at 10:16 AM.
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Old 29th October 2012, 11:57 AM   #28614
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Issues of differential stages, especially jfets, with common mode signals, are well known - effects of nonlinear input capacitance. Audio signals are not any special, they are just assymetric.
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Old 29th October 2012, 01:04 PM   #28615
bcarso is offline bcarso  United States
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Originally Posted by RNMarsh View Post
Fiber-Optic microphones: If you shine a light on a vibrating diaphram and pick up the reflected light via a f.o. to a detector.... you pretty much dont have to worry about noise, amps and Z and cable pick up of hum emi/rfi et al. Why arent more using them and developing them further for more recording appl? Why, why, why? -RNM
Well in your defense you did qualify your statements with the words "pretty much". I wasn't suggesting that the use of photons and optical detectors was unfeasible, just that a sweeping generalization about photonic techniques eliminating "noise, amps..." is simplistic and not, on the face of it, guaranteed of superior performance.

The optical detectors will require preamps with their own noise issues. Using more light will help to a point. Being able to remote the electronics may be useful in specific circumstances.

" Why arent more using them and developing them further for more recording appl? Why, why, why?"

Why aren't people using them? Perhaps because they don't work as well, are more cumbersome, require more power? The fact is that, already, the thermomechanical noise of diaphragms and the Brownian motion noise of room temperature air is in excess of the contributions of the best JFET preamps --- and we're not even talking about other ambient noise in the best studios.

There is a prevalent notion that there is something about using light that somehow trumps other electronic approaches. And indeed there are powerful benefits with photonics in certain cases, but the techniques have their own subtleties and tradeoffs. Try to get good signal-to-noise out of an optocoupler for example. It is nontrivial.
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Old 29th October 2012, 01:53 PM   #28616
RNMarsh is offline RNMarsh  United States
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I seriously doubt that recording studio staff have ever heard of them let alone tried one.
Speculation and guessing isnt useful.... I can do that myself.
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Old 29th October 2012, 01:58 PM   #28617
SY is offline SY  United States
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You can also read their spec sheets, which will give you a clue.
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Old 29th October 2012, 02:36 PM   #28618
morinix is offline morinix  United States
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Quote:
Originally Posted by RNMarsh View Post
The microphone is not for any one appl. These are low distortion, wide bandwith mics.... not any less suitable than "measurement" mics cannot be used for recording music. Try them and learn. -RNM
So you have used them? Care to post sound clips?
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Old 29th October 2012, 02:41 PM   #28619
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You can also read their spec sheets, which will give you a clue.
I had a look to the Optoacoustics site.
Imagine, a mike manufacturer with NO DATA.
They show somewhere a captor witch is just a piece of acrylic... so it has to be sensible to ambient light variation ? hum, what about the 50 or 60 hz from neon tubes ?
No response curve, no directivity curve, no available dynamic nbr, no signal to noise ratio nbr , no distortion percents, not a word on the technology used, digital or analog...

I figure we have made a misunderstanding, they produce micro lights...
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Last edited by Esperado; 29th October 2012 at 02:48 PM.
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Old 29th October 2012, 02:53 PM   #28620
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t is more serious on the Sennheiser site.

Polar pattern: omni-directional
Optical fiber: multimode 200/230 µm
Frequency response: 20 Hz to 40 kHz (±6 dB)
Sensitivity: 15 mV/Pa
S/N related to 1 Pa sound pressure: > 50 dB(A)
Maximum sound pressure: 134dB
Amplification: infinitely variable in the range; +/-15 dB, switchable in steps 0 dB, +20 dB, +40 dB
AF output level: 15 mV/Pa (potentiometer in mid position, switch set to 0dB)
Output impedance: approx. 330 ohms asymmetrical, 660 ohms symmetrical
Current consumption: 120 mA
Operating temperature range - microphone: -10°C to +70°C; central unit: 0°C to 40°C __________________
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