Lengthy mic settling time after power up / reset - Nano BLE 33?

[kleydon]

I'm using the Nano BLE 33 Rev2's on-board microphone (MP34DT06J) with the PDM library and vanilla setup code (tutorial here), and am noticing there is an extremely long "settling time" before values from the microphone are trust-worthy.

When I first turn on the board (or perform a hardware reset), the microphone values are incorrect for roughly the first ~3.5 seconds. (Values start high, and gradually settle, over the course of this ~3.5 seconds).

Is the source / reason for this "settling time" understood? (Is there buffering within the microphone hardware? Within the PDM library? Some sort of digital filtering?)

Has anyone found a fix / work-around for the issue?

It seems unfortunate that a board that is so capable, and in other ways designed to be quick and responsive, requires such a long delay before the microphone produces usable values; I'd love to know what is going on here, and whether or not it can be remedied.