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Topic: Measure Sound Pressure Level with Automatic Gain Control (Read 239 times) previous topic - next topic

mondlos2

I have a Adafruit Max9814 Breakout board. Can I use it to measure sound pressure level in decibels?
I am not sure because it has automatic gain control. Can't that falsify the answer?
I saw an example with volts here: https://learn.adafruit.com/adafruit-microphone-amplifier-breakout/measuring-sound-levels
But I don't believe it delivers correct values and converts to decibels.

Grumpy_Mike

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Can I use it to measure sound pressure level in decibels?
No.
As you say the AGC screws you up.

mondlos2

It is strange that one of their examples is for sound level even if their board is not capable to do it correctly.
Does the AGC only get activated when clipping would be caused or does it always correct the values?
If not you could at least use it for sounds that are constantly quiet enough.

Grumpy_Mike

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If not you could at least use it for sounds that are constantly quiet enough
What part of no are you having trouble with?

DVDdoug

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But I don't believe it delivers correct values and converts to decibels.
Once you get the right breakout board (or microphone & circuitry) you'll have to do the conversion to dB in software.    It usually requires a known-good SPL meter to calibrate it.   i.e.  Find the voltage or DAC reading for a known SPL and use that as a calibration reference.

There's some tricky stuff to making an accurate  SPL meter and it's been discussed before so you might want to search the forum for "SPL meter".

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