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Low output volume and severe distortion with DAC2HD + DSP add-on

Oskar Jonson

January 08, 2021 17:34

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Hello, 

I'm using a raspberry pi4 with DAC2HD + DSP add-on with hifiberryOS version 20201213 and dsp add on program version 13.

I have a problem with low volume output, it is roughly half compared to other sources when set to 100% (e.g. chromecast audio, TV etc...), is it possible to increase this?

Also, when the volume is 100% there is severe distortion, however this goes away by reducing volume to ~ 90%. It also disappears when I remove my eq filter (which has a peak gain of +10dB) so I suspect there is some headroom issue in the DSP? How do I solve that? 

Thanks

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7 comments

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  HiFiBerry team January 09, 2021 04:50

  That's perfectly normal that you will have distortions when you increase the signal by with an EQ 10db. Before doing so, you need to reduce the level bei 10dB if you want to use a full level signal. A DAC can't deals with anything higher then 0dbFS. Therefore, the input of the DAC (which is the output of the DSP) needs to be lower.

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  Oskar Jonson January 09, 2021 07:15

  Ok, does that mean that if I want to be able to set the volume to 100% in the GUI of hifiberryOS I will have to use an EQ that only lowers output? I.e. instead of peaking bass I have to reduce highs etc. 

  Also, how does all of this relate to the low output volume (even with flat EQ)? The spec. of the DAC2 HD states a maximum output voltage of 2.1Vrms so it should be able to produce the same output as my other sources

   

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  HiFiBerry team January 09, 2021 07:20

  You can use peaking eqs, but you have to reduce the overall volume at some point.

  I can't say anything about your "other sources" as I don't know these. Is the output volume ok without the DSP?

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  Oskar Jonson January 09, 2021 08:39

  Sorry, I was mistaken regarding the volume output. It is simply the volume slider that behaves differently in spotify depending if you are connected to hifiberry or chromecast audio (e.g. 50% is much louder on the chromecast compared to 50% on the hifiberry, but at 100% they are the same)

  I'm still confused regarding the EQ level in the DSP. You say that I can use peaking EQs, but how do I ensure that the DSP does not exceed 0dBFS? Just reducing the volume slider some arbitrary amount does not seem very robust to me. Is there some best practice here?

   

    

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  HiFiBerry team January 11, 2021 12:09

  You can decrease the volume by a specific decibel value in "Channels and limits"

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  Oskar Jonson January 11, 2021 12:34

  That's great, I'll do that. How many dB of headroom is it in the dsp? I.e. how large EQ gain can I use before i have to reduce the volume?

• 1
  
  HiFiBerry team January 11, 2021 12:39

  The DSP itself has enough headroom for all practical applications, you don't have to care about this. But the DAC doesn't have any headroom. If you try to play a signal that has more than 0dbFS level, it will distort. Usually there is always some headroom in the recordings. You might need to experiment a bit what works best for you.
  If you reduce the level by 10dB before adding a peaking eq with 10dB you are always on the safe side, but depending on your equipment and it's settings, it might volume might be a bit low.