THD measurement

Gavin49

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REW was already amazing when first released and somehow it keeps getting better and better. Thank you John!

Love the "plot harmonics at the harmonic frequency" option. Some recent graphs using it were enlightening even though the data is no different, just displayed differently.

I starting conducting some tests using a looped back connection. The generator is the source of a dual sine wave signal, to mimic 2nd harmonic distortion. Below is the RTA result.12KHz H2 is -11dB wrt the 6KHz fundamental. Noise, H3 and beyond are in the weeds. I expect to see a THD+N of 28ish% but is shows 0.20%. "get fundamental from generator" is not checked. Looks like REW might be thinking I'm doing something else and/or my setup is incorrect?


1734282245136.png
 

dcibel

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REW knows that you are using a mutlitone signal, whether the "get fundamental from generator" option is selected or not. That's why the distortion window clearly shows F1 and F2 values. For what you are trying to do, you may want to export the generator signal to file and play back from an external audio player.
 

John Mulcahy

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When you select a dual tone signal REW configured itself for IMD measurements. If you want to generate a sine with distortion use the tone generator and select the option to add harmonic distortion.
 

dcibel

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I keep forgetting that option exists, much better / easier solution that what I suggested above.
 

Gavin49

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When you select a dual tone signal REW configured itself for IMD measurements. If you want to generate a sine with distortion use the tone generator and select the option to add harmonic distortion.
Another very useful function, that I also missed. Sorry and thank you!
 
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