PDM peripheral's sampling rate at clock rate of 1.032 MHz

Question

I'm using the nRF52840 and the PDM peripheral. The sampling rate at a clock rate of 1.032 MHz is 16kHz per the documentation. I want to make sure I understand the difference between the PDM clock rate and the effective PDM sample rate Am I right in thinking that the maximum sound wave frequency I can measure is then limited to 8 kHz? If that is correct thinking, is there any thing I can do to increase the sample rate other then utilizing undocumented/non-guaranteed nrf_pdm_freq_t values that I place in the /modules/nrfx/hal/nrf_pdm.h file?

ovrebekk · Accepted Answer

Hi 
 The PDM sample rate is limited to 16kHz which as you say limits the audio frequency to 8kHz (normally a bit less as you need to filter the sound signal to avoid aliasing). 
 The main use case for the PDM interface is for handling voice input (remotes with support for voice commands for instance), and for this purpose 8kHz audio is sufficient. 
 If you need a higher sample rate I would recommend finding a microphone or ADC with I2S output instead, as the I2S interface supports sample rates up to 48kHz. 
 Best regards Torbjørn

matty · Answer

Thank you

PDM peripheral's sampling rate at clock rate of 1.032 MHz

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