Tonality control adds a lot of noise (Bass only, in fact)

RaoulJ

• November 25, 2023 15:48
• Edited

Measuring the behaviour of the tone control on my Node 100 with BluOS 4.2.0, I see a few interesting things:

1. Level is decreased by approx. 6dB 
Good ! Then no risk of overload by pushing Bass/ Trebbles. That's how it should work.

2. Enabling tone control has a negative (but not dramatic) impact on SNR
Not so good, but quite expected

3. Changing trebble setting has no signficant additional effect on noise level than just activating tone control

4. Changing bass setting; whatever the value, literally KILLS the SNR
We speak of a -30dB SNR impact for ANY setting.
-6dB, -0.5dB, +0.5dB, +6dB...
Well, except for 0dB.

I guess it's kind of a bug.
Could you check and fix that, please ?

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• 

  RaoulJ

  • November 25, 2023 13:26
  • Edited

  OK, so adding more details
  
  I measured using Audio Precision Multi Tone 32 signal (24 bits 48kHz)
  The signal is in a WAV file on my computer, shared with the Node 100.
  It's then played through SPDIF output to an RME ADI-2/4 Pro SE.
  The RME is connected to my PC with USB
  So the signal path is purely digital: No analog conversion.
  Measurement is done using Virtins Multi Instrument 3.9.9.2
  NB: Don't worry about the Voltage measurement. It's just wrong.
  
  Here is the measurement when tone control is disabled
  
  
  Here it is when I switch Tone control on, but all controls are on 0dB
  
  
  We lose only 10dB (6dB of which are due to the -6dB level change to avoid saturation)
  That's pretty good actually.
  
  Now with some Trebble change (-6dB)
  
  
  This has very little impact. This is the worst case scenario: all other trebble settings are better.
  
  But what happens if we dare to touch Bass control ?
  
  
  It doesn't even cover the CD dynamic range - and still in full digital 24 bits !
  We've lost 36dB of dynamic range just by modifying bass level by 0.5dB.
  
  All other bass settings give similar results.

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  RaoulJ

  • November 25, 2023 14:22

  Of course, that does have very little impact on the analog output, since this one is VERY weak...
  But I only use the Node 100 with its digital output, anyway.
  
  

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  RaoulJ

  • November 25, 2023 15:54
  • Edited

  Measuring the same signal through Analog output, the best result we get is for -12dB volume
  
  

  because at 0dB or fixed volume, the output is saturating:
  It's 0.23% TD+N, which is not good
  
  As from -1dB (2 notches below max level), we get results close to the "best".
  

  Again, this saturation only occurs in the Analog path.
  There is no such thing in digital domain, as the measurements in the post above show.
  
  Bottom line: with analog output, don't use fixed volume, but lower the level by 2 notches at least for best results.
  
  By the way, there is very little impact of the volume control on sound quality.
  We can check that by comparing the (pure digital) output through SPDIF at full / fixed volume (identical)
  
  

  to the results with a small level decrease
  

  This difference is negligible, of course.
  So the level control itself is well implemented.

   

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