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MEMS microphones Forum Discussions

User21588
Level 1
First question asked
Level 1
Hello,

I am testing an IM69D130 microphone on a Shield2Go evaluation board.

I am getting something that I would call quite a large DC offset and that is heavily fluctuating over time.

It is the same using the I2S output of the ADAU7002 ic on the eval board or the direct PDM output of the microphone itself.

The datasheet doesn't mention anything like that at all. Is that really to be expected? (When testing with a similar product from a different vendor it does not happen).

Sine wave recored to a wave file and opened in Audacity:
5075.attach
You clearly see the movement up and down.

Graph of the min (blue), max (red) and avg/offset (green) for every 3000 samples for a total of 30 seconds. When recording a constant sine wave.
5076.attach

When you subtract the green line the others would look clean. So yes one can probably do some form of post processing/filtering. Not sure how good that would work because it fluctuates so much.

Any ideas?
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2 Replies
davegravy
Level 1
5 sign-ins First reply posted First question asked
Level 1

Did you ever find a solution to this? In my experience with non-mems based microphones, they often incorporate a highpass filter somewhere between 0 and 20Hz to eliminate inaudible low frequency components. 

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GeorgeT
Moderator
Moderator 25 solutions authored 10 likes received 50 replies posted
Moderator

Hello @User21588 ,

Could you please tell us the following information for understanding the problem better?

1. Which microcontroller is used in this work?
2. How are you recording and saving the audio in wave format?

Thanks and regards

George

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