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Low-distortion Audio-range Oscillator
Low-distortion Audio-range Oscillator
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Old Today, 06:01 PM   #8101
jan.didden is online now jan.didden  Europe
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I could try that!

Edmond, if you are reading this, how do I do that?

Jan
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Old Today, 06:04 PM   #8102
Edmond Stuart is offline Edmond Stuart  Netherlands
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Default Notch filter compensation

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Originally Posted by 1audio View Post
Jan, to push the envelope can you connect a soundcard to the notch monitor out from the AP and use Diana to look at just the harmonics? Edmund has a routine for correcting for the insertion loss of the notch. Diana can separate the harmonics and even reconstruct the phase accurate error.
But I'm still busy with this: DiAna, a software Distortion Analyzer
The problem is how to calculate or estimate the insertion loss at the fundamental by means of interpolation. Perhaps B-splines again?

Cheers, E.
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Last edited by Edmond Stuart; Today at 06:18 PM.
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Old Today, 06:15 PM   #8103
Edmond Stuart is offline Edmond Stuart  Netherlands
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Default Notch filter characterization

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Originally Posted by jan.didden View Post
I could try that!
Edmond, if you are reading this, how do I do that?
Jan
Hi Jan,

See: DiAna, a software Distortion Analyzer and further. However, be aware of possible pitfalls like overloading etc.

Cheers, E.
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Old Today, 06:31 PM   #8104
phofman is online now phofman  Czech Republic
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Edmond: in my distortion compensation project I tried estimating the RC filter component values by nonlinear regression (curve-fitting) 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 curve-fitting, 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 curve-fit complex values which makes the equations much simplier.

The equation for RC LPF was trivial with complex numbers nonlinear-compensation/lowPass.m at 078fb9f1c572568f343bb0bd652b2ea55874896d * pavhofman/nonlinear-compensation * 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 nonlinear-compensation/testLP.m at 078fb9f1c572568f343bb0bd652b2ea55874896d * pavhofman/nonlinear-compensation * GitHub

The core of my algorithm is based on nonlinear curve-fitting and the fitting precision is extremely good (sum of squared errors at 1e-20), 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.
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