monitoring environment ?

[John Jones]

Hi 

I have searched a LOT but I can not find if Nordic can record audio with high enough fidelity to a SD card (I have seen in the SDK how to attach a SD card ). 

I want to be able to record fogs/owls etc  (the audio environment)  at 48kHz sample rate is this possible ? 

what is the maximum sample rate of the ADC ?

Would it be possible to apply a Goertzel filter for real-time classification algorithms. I would like to filter specific terms of a fast Fourier transform on temporarily buffered audio samples without the computational expense of a complete transform. The outcome of each algorithm could then be used to trigger recordings to a microSD card. Has anyone completed anything like this ?

Thank you for your considered response.

Regards

John Jones

[bjorn-spockeli]

HI John 

I want to be able to record fogs/owls etc  (the audio environment)  at 48kHz sample rate is this possible ? 

We have two audio intput interfaces, PDM and I2S on the nRF52 series. Do you want to use a PDM microphone or do you have a dedicated ADC with an I2S interface? How large is each sample?

PDM only allows for a 16kHz output, see PDM — Pulse density modulation interface. The I2S peripheral supports a LRCLK of upto 48kHz with 8, 16 and 24-bit sample width, see I2S timing specification

 Or do you mean writing the data to the SD card? We do have a SD Card Example which uses the SPI peripheral which supports a clock frequency up to 8Mhz.

what is the maximum sample rate of the ADC ?

 The maximum sample rate of the SAADC is 200kHz, see https://devzone.nordicsemi.com/f/nordic-q-a/15381/how-to-implement-max-sampling-with-saadc.

Would it be possible to apply a Goertzel filter for real-time classification algorithms. I would like to filter specific terms of a fast Fourier transform on temporarily buffered audio samples without the computational expense of a complete transform. The outcome of each algorithm could then be used to trigger recordings to a microSD card. Has anyone completed anything like this ?

We do have a FPU FFT Example in our SDK, I suggest that you take a look at that.  Triggering writes to a SD card should not be an issue by using Software interrupts, i.e. the Event Generator Unit(EGU) peripheral. 

 Best regards

Bjørn