Noisy record for STMicroelectronics MP45DT02 digital mems microphone

audiomems-microphone

I bought STM32F4DISCOVERY board and I developed a software that records .wav file using MP45DT02 MEMS microphone on this board. .wav files that I record are really good (almost no noise).

I designed a board based on the schematics of this evaluation board. When I used the same software, I have high noise at the background. I also can't record my voice unless I shout or scream. You can listen the record by this link.

I have 3.3 volts on the board and the capacitors are appropriate in terms of value and closeness to the microphone.

I have two boards and I have the same problem on both boards so it seems to me that the problem is systematic.

Could it be a problem of soldering or PCB cleaning after production of the board? Could it be a problem of noisy power supply? What could be the reason?

Edit: Below is the spectrum analysis of the two records. (Green: Eval board | Blue: My board)

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Edit 2: Below is the channel meter of the two records. (Top: Eval board | Bottom: My board)

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Best Answer

It seems that microphones were damaged during PCB cleaning process. The producer puts spray on the PCB after production and small particules may enter inside the sound inlet during the process. When we changed the microphones, they started working. This explains the problem.

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