PDM Library - Random Microphone Spikes on Nano RP2040 Connect

[julienmartin84]

Hello!
I have been playing with the PDM library and the bundled PDM example on an Arduino Nano RP2040 Connect.

v2.1.0: no spike artifact
v2.2.0: spikes artifacts
v2.3.1: spikes artifacts

Screenshot 1: no noise in the room

Screenshot 2: was playing a clean sine wave near the arduino

The spikes seem to disappear when using a frequency of 8kHz or less instead of the 16kHz default of the example.
I describe the problem in details here
In this Arduino forum topic, user Klaus_K identified some change that occurred with 2.2.0 and that could maybe cause the issue.

[facchinm]

Hi @julienmartin84 ,
thanks for taking the time to report the issue here.
The glitch is due to the new clock frequency provided to the microphone (starting from c97ec7e), which is above the nominal maximum at 16khz sampling rate

I pushed #302 to fix this, it would be awesome if you could test it and report if it really fixes the issue 😉

[julienmartin84]

It is working correctly after i updated Arduino Mbed OS Nano Boards
Thank you!

[RickorDD]

I have a problem with my Arduino Connect PR2040 and the internal MIC.
SerialPlotterExample and Edge Impulse runs not with Decimation = 64 only with 128 but there the Spikes.

https://forum.edgeimpulse.com/t/arduino-nano-rp2040-help/4638/22