Measure Total Harmonic Distortion with Noise easily with ARTA

[@TrystansWorkbench]

*Comment* *From* *JohnAudioTech* That's about what I'd say my FeelTech measured at. Have you baselined your equipment? By that I mean tested the sound card with a low distortion source to see what it adds to the measurements? *Reply* *by* *Trystan* That's great. I've baselined it as far as doing a loopback test taking the output of the soundcard with a generated 1Khz to the input of the soundcard. This gives be a THD+N of 0.05%. From that, I can't tell if the THD+N is being generated or if it's the input that being distorted. I've also run your test tones WAV files kzbin.info/www/bejne/mYOUha1umbZkhKc through the loopback, and your 1%, 0.5% match up, then your 0.3% measures 0.31%, 0.2% as 0.21%, 0.1% as 0.13% and the pure one as 0.06%. It gives reasonable confidence in ARTA and a cheap USB Soundcard as a starting point. In planning on building a bulb stabilized wien bridge oscillator - so hopefully that will help. Thanks for your comment John! (I managed to delete the video off the channel - so that's why I've added the comment back!)

[@jatza07]

Why 1k resistor ?

[@TrystansWorkbench]

It's to provide a small load for the signal generator as the sound card has a high impedance input.

[@jatza07]

@@TrystansWorkbench thank you. Another question - when I plug my FG-100 DDS Function Generator I get same THD+N = ~0.3%. Suprisingly using iphone and appliication on it , for the same voltage I get 0.018% !!! Does it mean my hardware funtion generator itself produces some harmonic distortion? I would say yes. Question if 0.3% comprimises it as a tool to measure THD of an amplifiier. THank you :) PS. I am a beginner in this field.

[@TrystansWorkbench]

@@jatza07 So am I ! Yes the DDS function generators synthesize a waveform, so there will inevitably be distortions. Your iPhone is impressive - but bear in mind a function generator has to generate radio frequencies too, but your iPhone only has to cover audio. Search for a "Victor Oscillator" for a very low distortion oscillator ( a Wien Bridge Oscillator ) which you can buy. In measuring distortion in amps, then subtract off the measured distortion of the oscillator driving it. Also remember to take an attenuated tap off the speaker (or load) you are using. I'm no expert though, have fun!