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22nd November 2019, 06:01 PM  #8101 
diyAudio Member
Join Date: May 2002
Location: Westende Resort, BE coast

I could try that!
Edmond, if you are reading this, how do I do that? Jan
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22nd November 2019, 06:04 PM  #8102  
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Join Date: Nov 2003
Location: Amsterdam

Notch filter compensation
Quote:
The problem is how to calculate or estimate the insertion loss at the fundamental by means of interpolation. Perhaps Bsplines again? Cheers, E.
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http://www.dataodyssey.nl/ Last edited by Edmond Stuart; 22nd November 2019 at 06:18 PM. 

22nd November 2019, 06:15 PM  #8103  
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Join Date: Nov 2003
Location: Amsterdam

Notch filter characterization
Quote:
See: DiAna, a software Distortion Analyzer and further. However, be aware of possible pitfalls like overloading etc. Cheers, E.
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22nd November 2019, 06:31 PM  #8104 
diyAudio Member
Join Date: Apr 2005
Location: Pilsen

Edmond: in my distortion compensation project I tried estimating the RC filter component values by nonlinear regression (curvefitting) of the respective circuit equations to the measured transfer values (amplitude and phase shift), initialized with imprecise values of the circuit components. Worked very precisely. Once the circuit model has the exact component values determined by curvefitting, you can probe it for any parameter at any condition.
In your case the equations would be more complicated since the filter is a bit more complex, but you could offer a few typical circuits + user would enter the nominal component values. Good libraries can curvefit complex values which makes the equations much simplier. The equation for RC LPF was trivial with complex numbers nonlinearcompensation/lowPass.m at 078fb9f1c572568f343bb0bd652b2ea55874896d * pavhofman/nonlinearcompensation * GitHub Finding exact values of R1, C1, Rin to fit the measured transfer values (in my trial just randomized exact values) were only several lines nonlinearcompensation/testLP.m at 078fb9f1c572568f343bb0bd652b2ea55874896d * pavhofman/nonlinearcompensation * GitHub The core of my algorithm is based on nonlinear curvefitting and the fitting precision is extremely good (sum of squared errors at 1e20), of course provided the equations are correct. I am sure it would work, especially if you let some software derive the equations for you. Maybe some interpolation will work too, but definitely not as accurately as the circuit model fitted to measured values. On the other hand you do not need any major precision in your interpolation, it does not matter if diana measures values with a few percent of relative error. Just 2 cents. 
22nd November 2019, 07:11 PM  #8105  
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Join Date: May 2002
Location: Westende Resort, BE coast

Quote:
Jan
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22nd November 2019, 07:37 PM  #8106 
diyAudio Member
Join Date: Aug 2016

Latest version of my THD calculator
Latest version of my THD calculator. What's new?
 Import possibility from ARTA  Selection of harmonics 
22nd November 2019, 09:52 PM  #8107 
diyAudio Member
Join Date: May 2002
Location: Westende Resort, BE coast

Ralf, I'm trying to figure out the calculations.
For H2, the measurement (I think) is 94.6dB. The notch atten for H2 is 8.8dB. So the actual H2 is then 85.8dB, right? The amp gain is 40.1dB. That gives me 125.9dB. But the calculated column says 124dB. Maybe I miss something, but I can't solve it. How do you do it? Edit: if I figure in the atten from 600R Zout and 2.5k Zin I get the missing 1.8dB. But that would be for both the (notched) fundamental as well as the harmonics, so should make no difference. I think ... Jan
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22nd November 2019, 10:31 PM  #8108 
diyAudio Member

Edmund, could you enter the fundamental attenuation manually? What I did was plot the attenuation curve for harmonic correction and adjust for the loss/gain in the Shibasoku output which is fixed.
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22nd November 2019, 10:48 PM  #8109  
diyAudio Member
Join Date: Aug 2016

Quote:
Your conclusions are correct. The value of the attenuated fundamental doesn't matter in the calculation. I do the calulation with the unattenuated input fundamental. This has the advantage that I don't need to know the fundamental attenuation of the notch filter. In addition, if the oscillator frequency deviates from the notch frequency, then the attenuation is different again. 

23rd November 2019, 07:53 AM  #8110  
diyAudio Member
Join Date: May 2002
Location: Westende Resort, BE coast

Quote:
Jan
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