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Noisy signal on Hifiberry outputs

Karl-Heinz Dahlmann

March 16, 2023 18:01

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I am bit disappointed about Hifiberry. First installation was very frustrating due to missing information what driver to use and what (raspi driver) not to use. It is now working with a clean installation of Raspi OS-Lite 64 bit without desktop (remote only). One important thing to hear music is to disable DRM VC4 V3D Driver (!).
I can not find any hints in the sparely installation documentation.

Okay it is running now and putting out music. But anyway I am also disappointed about the noise on the output. And there is no defect this noise is existing when nothing plays and also when something plays. I tried two different (new) Raspberry Pi 4 with 2 new Hifiberry. This problem seems to be system immanent. It is not heard as frequency is above 20 kHz but if you want signal processing this can be very disturbing. We are talking here about short pulses every 50us with an amplitude of about 1V (!). 

This noise is even with no running playback (silent).

This is when it is overlayed to music.

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7 comments

• 0
  
  Karl-Heinz Dahlmann March 16, 2023 18:24

  Okay - this comes from the power supply, but - when connecting audio hardware to a computer, is there no filtering made ??
  
  This is audio output from my smartphone Google Pixel 6 - clean.

  

• 0
  
  HiFiBerry team March 17, 2023 06:59

  What driver to use and how to disable onboard sound (including HDMI) can be found on our web site:
  https://www.hifiberry.com/docs/software/configuring-linux-3-18-x/ 
  
  This explains the driver settings for every card.
  
  As you're talking about "HiFiBerry", I have no idea what card you're using. However, I also won't interpret your scope pictures. My best guess is just a poor power supply or incorrect grounding (a problem that you won't see with your mobile phone as there is no ground connection). 
  
  As our sound cards are designed to work at frequencies up to almost 100kHz, there can't be any analog filtering below this frequency. 
  
  

• 0
  
  Karl-Heinz Dahlmann March 17, 2023 12:40

  Thanks for answer. I am using the DAC 2 Pro.
  Yes the used power supply was bad but choosing a better one, gave me noise on the 5V of about 10mV rms. I can measure it at the output. When I talk about filtering then I mean filtering the power supply. I guess you use a LDO and some very small capacitances in 0402. Anyway an LDO is not a useable filter for high frequency noise. So filtering the power supply does not effect your bandwith of the audio outputs.

  When a product is called HiFiBerry I (and probably other customers) I have expectations on the result of the implementation in the proposed environment (Raspi). When you state noise level for the product it is just the same data of the datasheet of the PCM5122. This is the best value someone can get under laboratory conditions but not in real life. With 10mV rms rest noise you can get a THD of about 0.5% or -46dB with a maximum output amplitude of 2V rms. Why this is important - in silent periods of music (like classic parts) THD goes easily up to -25dB when output amplitude is only 200mV. Just my 2 cents on the product which could be made better investing a little bit in power supply filter components. ;-)

• 0
  
  HiFiBerry team March 17, 2023 12:51

  I can ensure you, we (and also others) measured THD and THD+N and also power supply noise. Definitely a lot better than your setup. You're probably injecting noise to ground at some point of your setup and no filtering of any power supply lines will do anything about it. 
  There is some problem in your setup, but I can't debug your measurement setup. 

• 0
  
  HiFiBerry team March 17, 2023 13:03

  Just some thing that is a regular cause for ground noise: Connecting ethernet with shielded cables. That would be my starting point to find the root cause, but there can be all kinds of other sources for it.

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  Karl-Heinz Dahlmann March 17, 2023 16:30

  Nope - there is nothing connected than just a RPI4, a Hifiberry DAC 2 Pro on top and my scope. And the power supply. All configuration is done via WIFI - so no noise from outside. 

  For me is okay now as I do not have a shielded room to do further measurements. But in practice you will always have distortions more and less depending on equipment and location. I have now distortion rms of about 5mv which is near the border to measure with my equipment now.

  With no power connected:

  

  with power connected with a quite good power supply:
  
  

  and detailed noise in higher time resolution:
  
  

  This status is okay now for me and much better than yesterday with a horrible chinese power supply (maybe the cheapest one can get - but (!) officially sold in germany).

• 0
  
  Karl-Heinz Dahlmann March 17, 2023 16:33

  This topic can be closed - up to you.