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:
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.
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.
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.
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