ADAU1961 high hiss noise at the output

We are testing ADA1961 for the first time.
The issue is that at the output of ADAU1961 we have a rather high hiss noise, which is only affected by the output mixer volume. When switching off either ADC or DACs, the noise is still there. When setting down the output volume, the noise is reduced accordingly.
The same noise is on both outputs LOUTP/N and ROUT/N

Any hints?
HPF filter in ADC control R19 is enabled

Thanks
  • 0
    •  Analog Employees 
    on Aug 18, 2021 1:46 PM

    Hello joanamate,

    Are you using SigmaStudio to control the codec?

    If you are can you zip up and attach the project file?

    Dave T

  • Hi Dave,

    thanks for prompt reply. I attach the project file

    Test_1961.zip

  • 0
    •  Analog Employees 
    on Aug 19, 2021 7:37 PM in reply to joanamate

    Hello joanamate,

    It is difficult for me to run this project exactly as you are since you are using an ADAU1452 using I2C. But it was good to see your project. 

    You had mentioned that the HPF is engaged. In the project it was not engaged but I think that is why you mentioned it. It is a good idea to use the HPF located in the ADC. 

    For gain through the project it looks like there is only the 2dB right at the start of the signal flow. I see that all the EQs in your project is set to bypass so that is good, but what I would like for you to do is to test this bypassing the entire signal flow. So I modified your project to do that. 

    On the codec side. Which input are you actually using? I see you are only taking in the left channel in the DSP but in the codec you have the AUX input active and the LINP input. The gains are set to nominal so that is good. Also, I have noticed that on the playback side if you mute the DAC and all other inputs to the mixer is active there is a lot of noise. It is a high impedance node and will pick up noise if nothing it feeding into the mixer. So just mute the audio out of the DSP, you have mutes on each output, and see if it is still noisy. 

    The last thing is to understand the nature of the noise. Have you done an FFT of the noise? 

    Test_1961-DT Edits.zip

    Dave T 

  • Dave, thanks for the detailed answer. We will perform the mentioned tests and let you know.

    Regarding our questions: we are using just one input to the ADC (the LINP) and in single mode, not differential. The AUX is not used.

    I will peform also the FFT of the noise. It might take a couple of days, since we have to care about other projects at the moment

  • 0
    •  Analog Employees 
    on Aug 20, 2021 3:11 PM in reply to joanamate

    Hello joanamate,

    If you are not using the AUX input then you need to shut it off. That certainly can be a noise source. 

    Dave T