High Digital Noise Floor in SigmaStudio 4.6 with EVAL-ADAU1787Z board

Hello, I am having a big issue on SigmaStudio 4.6 with the external board EVAL-ADAU1787Z. From the ADC (Analog Input 2/3) I get a Noise Floor in form of a random and digital noise (sometimes similar to white noise, sometimes more digital with single tones that appear and disappear). From time to time (every few minutes or so) I also get louder noise similar to white noise, that stops only if I change or touch the master volume control of my Dell laptop. The softer background noise is instead always present, and it is on the range of -50dB FS, measured with a level detector in SigmaStudio out of the ADC block. Clearly I can' t work on my audio project with this noise problems. I am wondering if you have experience this before and if you have any suggestion on how to solve it.
I have already tried to swap USB and Audio cable, as well as evaluation board (with another EVAL-ADAU1787Z) and USBi board, but the problem is still the same. My computer is a Dell laptop with Intel Core i5 and Windows 10pro x64. Any help would be crucial at this point because I really do not know how to proceed in my project. Thank you very much in advance for your time and effort.
Guido Baldovino
  • 0
    •  Analog Employees 
    on May 11, 2021 5:22 PM

    Hi Guido,

    Is it possible to send the capture of the noise? Also would be best if you could send the SStudio project. Maybe some settings are incorrect.

    The most important is to check if the PLL is locked in the READ tab in SStudio. Without the master clock the chip will not enable.

    I assume you are feeding the analog input from the Laptop and measuring the HP output. Remember the HP output is differential. We have provided the SE output just for demo purpose and connecting Single Ended Headphones using 3.5mm jack. 

    Let me know if any more questions.



  • Hello Rajeev, thanks for the reply. Could you elaborate a bit on the PLL setup you mentioned? If I understand better I can check further on it. Honestly, I can share any of my SS projects, but the high noise is always present, no matter how the project is, just whenever I wire something out of the ADC and into the stereo output. As soon as I compile, I get a loud digital noise, which gets very very loud (like the sound of an open circuit so to speak) frequently, and goes down eventually by moving the computer volume cursor on my Dell laptop. Despite this loud temporary noise, the digital noise floor that I get out of the ADC in SS is anyway annoying and makes it impossible to work. I am gonna share again the info I can, hoping to get more help from you. 

    I am using a Dell laptop with Win10 with the preinstalled audio drivers by Realtek and the additional preinstalled software by Waves called MaxxAudioPro.

    I am using the external board ADAU1787 together with external board for USB communication. 

    I am sending audio out of my laptop into the board and listening through headphones, and running SS 4.6. 

    I have tried changing board, usb ports and cables, computer, audio cables, headphones, power electricity plugs, powering the board with external supply, changing project in SS, and probably other things but nothing successful so far. 

    I hope you may have a better idea on what it could be now, maybe someone experienced something like this before. Please let me know what I can do to provide a better way for  you to help me, thanks!

  • 0
    •  Analog Employees 
    on May 20, 2021 3:12 PM in reply to whiteguidow

    Hello Guido,

    Have you tried a different audio source? I think it is the laptop audio output combined with either a poor ground on the USB port, which is common, or in the case of an external power supply again, a poor or missing ground. Most external supplies are not grounded. So the digital noise present on the laptop audio output is finding a path to ground though the eval board and that is what you are hearing. I have noticed this with my setup and I rarely use my Dell company laptop as an audio source. I usually use the Audio precision or my personal MAC but even my MAC sometimes has too much noise. 

    First, just disconnect the audio input from the laptop to the eval board and see if it is quiet. Setup an audio source from within the DSP, an oscillator, and see if that is quiet. You can also try using a phone as a temporary experiment. 

    Once I did have a strange ground loop in the lab where if I used the Dell desktop lab computer to run and power the eval  board from the USB port and take the audio from the same computer I had a lot of noise. If I took the audio from a second desktop computer on the bench it was fine. So the ground loop and noise signal return currents was being setup when it was all on one computer but when I used the second computer there was no path for these noise currents so I could not hear them. 

    Dave T