RE: monitoring environment ?

bjorn-spockeli — Mon, 14 Oct 2019 13:28:41 GMT

HI John

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

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.

[quote user=""]what is the maximum sample rate of the ADC ?[/quote]

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.

[quote user=""]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 ?[/quote]

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