I figured out the issue, when setting the sampling bit width to I2S_DATA_BIT_WIDTH_16BIT esp-idf sets the word length to 16 bits as well, so a whole frame is just 32 bits, the i2s bckl was only 327 680 hz. I was expecting 64 bit clock cycles per frame, which would make the bckl 655360 hz. Just ...

I'm using an INMP441 i2s microphone ( datasheet ) and using the esp-dsp library and esp-idf 5.0.1 to create an fft series. I'm sampling at 10 240 Hz but I can't see any signals higher than about 2500 Hz, and the plot of the fft shows an alias around 2500 Hz as well. Is there some error in my i2s ...