Questions regarding digital filtering of audio signals

[RobHel]

Hello,

I'm using two nRF5340 MCUs with BLE5.2 audio in an application. I had a couple questions I hoped the Devzone could help answer.

1. On one of the MCUs, I was originally going to have the audio data exit the MCU via the I2S bus. This would then be fed into an external DAC. A DAC, not a codec or amplifier, as the DAC then feeds into op-amps for more external filtering of the audio signal. Instead, can the nRF5340 do this DAC aspect internally and the can the audio signal exit the nRF5340 as an audio (mono, single-ended) analog output?

2. Can double pole bandpass filtering be done in firmware to audio data?

Thanks,

Rob

[ovrebekk]

Hi 

1. There is no built in DAC in the nRF5340, no. You have a PWM module, but then you are limited to 8-bit resolution, and will need to find some way to filter out the PWM frequency externally, which doesn't make it suited for all but very simple audio applications. 

2. This should be possible, yes. The DSP and floating point units in the M33 core can be used to accelerate FIR and IIR filter calculations. 

I am not sure we have any examples for this though. I will have to look into this a bit more and get back to you. 

Best regards
Torbjørn