*Chapter 2 of my upcoming novel, Resurrection, is posted here.
One of the mistakes we make as an industry is measuring quantity vs. quality. We talk of the T in THD as if it really mattered when it doesn’t.
Total Harmonic Distortion (THD), when below a percent, is far less meaningful than what kind of distortion we are referring to. THD refers to the addition of related harmonics. Stimulate an amplifier with a test frequency then measure whatever is not the original test tone. Whatever’s left over are related higher-order frequencies in two flavors: odd and even. An odd harmonic of 1kHz is 3kHz. An even harmonic is 2kHz.
In the same way we do not like dissonance in music, odd-order harmonics grate on us, while even order products feel warm and welcome. But more important is what these tell us about the underlying circuit topology. A tube amp has higher 2nd than a bipolar design and we know they sound very different.
We would be well served to modify the accepted THD term to include a more meaningful measure. For example, THD-E and THD-O. We might then see a more relevant measure of an equipment’s performance based on measurement.
An amplifier with THD-E of 0.1% and THD-O of 0.01% is likely to sound better than another with THD-E of 0.01% and THD-O of 0.1%.
Now, I know…..the nerds reading this will say, “Wait!. If that is true, then why not just say an amp with THD of 0.01% would sound better than either?”
Because, my friends, as I have tried so often to suggest, these quantity measurements are not in themselves meaningful.
Quality metrics point to underlying causes that are meaningful, while quantity measurements are too broad to have meaning.
And that is the point.