<html><head><meta http-equiv="Content-Type" content="text/html; charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class="">It's actually pretty straightforward:</div><div class=""><br class=""></div><div class="">1. Put the sine wave through a notch filter tuned to the same frequency.</div><div class="">2. Look at resulting squiggle on a scope.</div><div class="">3. Assure that the notch filter is doing its job.</div><div class="">4. Fine tune the frequency to completely null out the fundamental.</div><div class="">5. Measure the amplitude of the resulting squiggle.</div><div class="">6. And report that as a percentage of the original sine amplitude.</div><div class=""><br class=""></div><div class="">By "Notch Filter" I mean a filter that can fully null out a particular frequency to zero. And of course doesn't add any distortion on its own.</div><div class=""><br class=""></div><div class=""> -- Don</div><div class=""><div class=""><div dir="auto" style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div style="color: rgb(0, 0, 0); font-family: Menlo; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">--<br class="">Donald Tillman, Palo Alto, California<br class=""><a href="https://www.till.com" class="">https://www.till.com</a></div></div>
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<div><br class=""><blockquote type="cite" class=""><div class="">On Nov 11, 2022, at 4:39 PM, Tiago Ventura via Synth-diy <<a href="mailto:synth-diy@synth-diy.org" class="">synth-diy@synth-diy.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="">Greetings folks!<br class=""><br class="">The technical literature in general, *whenever* it bumps into the<br class="">topic of sine wave generation techniques the difficulty of generating<br class="">such a signal is always mentioned. And then, several techniques and<br class="">circuits are presented and analyzed. The THD% of these circuits are<br class="">mentioned for comparison purposes.<br class=""><br class="">How the heck are these distortion levels measured or calculated in practice?<br class="">What are the main techniques and procedures applied in order to<br class="">measure the total harmonic distortion (THD%) of a given sine wave?<br class=""><br class="">The idea of using a second sine wave as a comparative reference of<br class="">what is "pure" is pretty obvious, but what kind of source would be<br class="">able to present an acceptable "purity" for this purpose? (a digital<br class="">source sounds ridiculous for this but I can't think about anything<br class="">else!)<br class=""><br class="">Remembering that it is essential to also calculate the accuracy of<br class="">this measurement. Are there other alternative techniques for making<br class="">such a measurement? Is there anything available in the technical<br class="">literature exploring this subject?<br class=""><br class="">Any thoughts/comments/suggestions would be greatly appreciated.<br class=""><br class="">Tiago Ventura<br class=""><br class="">Greetings from Porto Alegre/Brazil<br class="">-30.03376474999071, -51.238242916392814<br class=""><a href="https://www.instagram.com/psychoincorp/" class="">https://www.instagram.com/psychoincorp/</a></div></div></blockquote></div></div></body></html>