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Glitch in analog audio output when using I2S module


I'm using the NRF52832 with I2S module connected to TLV320DAC from TI. I've configured the DAC and I2S module successfully. I'm getting audio output (simple sine wave read from a table) but there is an impulse glitch in the audio signal. The glitch appears to occur at the end of every I2S buffer send. When I set the I2S TX buffer size to 250 samples, I see a glitch in the audio at the corresponding time interval. For example, 250 buffer size at 41666 sample rate, causes a glitch in the audio every 0.006 seconds. When I increase the I2S buffer size, the glitch period increases correspondingly.

I've checked my sine table interpolation algorithm. It looks good. I believe the problem is with the NRF52832 and not the DAC. The I2S buffer size is the only variable which seems to affect the audio glitch. Oh, I also tried using I2S slave mode where I program the DAC to send the I2S clocks to the NRF chip. That did not change the glitch though.

I recorded the audio output in Audacity. Take a look at the waveform and frequency spectrum...


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  • Typically you can choose between Release and Debug in SES by:

    The difference between the two is found by opening the project file in text editor, e.g.:

      <configuration Name="Release"
        link_time_optimization="No"    gcc_optimization_level="Optimize For Size" />
      <configuration Name="Debug"
        c_preprocessor_definitions="DEBUG; DEBUG_NRF"

  • Ah! Good to know thank you. I can confirm that those configurations certainly don't appear if you follow the nRF Connect SDK installation instructions, at least as of a month ago.

    I feel I'm probably not missing out on anything anyway, since "DEBUG_NRF" does not appear in the SDK anywhere:

    As far as I can tell, that define is obsolete. I think the current way to do it is CONFIG_DEBUG and friends but I'm working blind so I'm not sure.

  • Sorry, I forgot you were using NCS, my screenshot were for nRF5 SDK. In your case I guess you can add the following to prj.conf:

    # Debugging configuration
    # add asserts

  • Thanks for that Kenneth. Yes, I sort of barged my way into this thread not realising how isolated the nRF5 world was from the NCS world, so I'm sorry for the confusion.

    I appreciate that list of CONFIGs. Haven't been burnt so bad stepping into the unknown so many times in this project so far, I'm going to tread very carefully. Every CONFIG seems to have unintended consequences that soak up precious hours. So to be honest, unless a compelling reason comes up, or some really good documentation, I'm going to leave sleeping dogs lie! Great to have them to refer back to though.