We discuss a lot how measurements have little correlation to sound quality. One of the reasons for this, of course, is that most measurements were never designed to inform us how something actually sounds. Rather, the original measurement standards, like THD, were designed to help engineers know if the amplifier they were building was working well enough to even use. In other words, their original intent had little to do with what we rely on them to tell us today. Created for one purpose, morphed into service for something else simply because there were no better alternatives. For example, back in 'the day', when an amp designer could get his tube power or preamp's distortion below 10%, that meant things were working well enough to release to the general public. Over the years as designers were able to reduce this figure lower and lower, it became marketing material to help sell products. At no time I am aware of were THD measurements effectively used to judge the actual sound quality. They did, however, serve the marketing departments of stereo manufacturers quite well. Today we see measurement gurus jumping up and down about slight rises in tiny distortions occurring well below what humans can even hear. But why? Because they can? What evidence is there we hear any of these distortions? The first measurements that could begin to describe sound quality that I became aware of was inter modulation distortion (IM); and then only if it was high enough to cause trouble. Ever diminishing levels of IM are also meaningless when it comes to describing the sound of something. Yet they do make for good marketing material for companies and help measurement people have something to write down. Matti Otala, John Curl and Eero Leinonen in their famous 1976 paper on TIM, made one of the first serious attempts to measure what we hear and show a difference. But in general, we use what we have 'on the shelf' because, well, we can. Not that it actually makes any sense to do so. And that's what's interesting to me. In every case I can think of, measurement systems start out as simple means of quantifying one thing, then get morphed over for something else that makes no sense for the end game. We use them because they are there. Take our Imperial measurement system we are so fond of here and in the UK. It's a system we use only because we grew up with inches, feet and yards and while we might know of the far superior metric system, most of us are basically clueless about it. The 'Imperial' measurement system is based on nothing more than a few barleycorns yet - yet it stays with us - just like THD does to this day. Watch this video if you want a good laugh and explanation. Bottom line. Just because we CAN quantify something in a certain way doesn't mean we SHOULD cling to it as proof of anything.
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