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Microphone bandpass with unity gain design question.

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MasterT:
You can't get meaningful measurements results if mic is pushed out of specification. Output becomes very non linear, and reliability is in question.
PGA - programmable gain amplifier. What I think, you need some kind of acoustic damping material, that would ensure SPL never goes above 110 dB. Same time if loudness is low, uCPU would change PGA settings, driving gain up.
What is connected after amplifier? 24-bits good audio quality ADC may get you 114 dB dynamic range even w/o PGA.

floobydust:
Why are you rolling off the low end at 1kHz? There is significant sound energy below there, in both music and industrial noise.

There's different types of microphone capsules - cardioid, omnidirectional, noise-cancelling, so have some awareness of what your capsule and housing need to do to pickup what you want. Sensitivity is around -45 dB Pa.

You'll need to RC filter 3.3V power to the mic and 1/2Vcc divider otherwise all noise on that rail will get amplified.

Richard Crowley:

--- Quote from: alexg on July 24, 2018, 07:32:10 pm ---It is important that gain of this circuit will be 1 (unity gain), I want signal from mic remain not amplified, just filtered.

--- End quote ---
Standard practice is to boost mic-level signals to something around "line-level". That is because mic level is "down in the mud" and has a poor signal-to-noise ratio. There is no apparent reason to want to process the signal down at such a low level.


--- Quote ---Microphone will be biased so that in silence it can swing rail to rail with loudest sounds,
--- End quote ---
This appears to be completely contrary to your requirement that the "signal from mic remain not amplified".
"Rail-to-rail" implies amplification.  Unless your power rails are measured in micro-volts which of course is absurd.

alexg:

--- Quote from: floobydust on July 25, 2018, 02:42:45 am ---Why are you rolling off the low end at 1kHz? There is significant sound energy below there, in both music and industrial noise.

There's different types of microphone capsules - cardioid, omnidirectional, noise-cancelling, so have some awareness of what your capsule and housing need to do to pickup what you want. Sensitivity is around -45 dB Pa.

You'll need to RC filter 3.3V power to the mic and 1/2Vcc divider otherwise all noise on that rail will get amplified.

--- End quote ---
About 1kHz, that is a very good question, honestly I cannot justify it reasonably, the way I come up with that number is that I simply was triggering some noise around microphone while capturing waveform and was not particularly happy how lower frequencies sending ripples allover and when played with software filter in the scope I saw that once you trim off anything under 1kHz waveform is nice and symmetrical, so that is how I come up with 1k lower end roll off, for now I just want to make it work and see that I can sort of have control over it but I do admit that trimming off 1K is a bit too much, probably need to back it up to 500 or even 200Hz

As for power, I am using MIC94310, which is an LDO with ripple blocker technology they say,  it is super quiet and clean supply.

alexg:

--- Quote from: Richard Crowley on July 25, 2018, 03:00:52 am ---This appears to be completely contrary to your requirement that the "signal from mic remain not amplified".
"Rail-to-rail" implies amplification.  Unless your power rails are measured in micro-volts which of course is absurd.

--- End quote ---

Sorry, probably worded it wrong and used wrong terminology, in simple words what I want is to be able for microphone to swing all the way up to 3v as close as possible and down to 0v as close as possible if that makes sense.

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