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Original Message
RE: Help me understand why
Posted by tomservo on January 27, 2017 at 07:47:25:
Hi E-Stat
The importance of harmonic distortion originated in Radio engineering where broadcasting energy outside your assigned frequency was a big no-no. Here, what mattered was how much was outside the band and Total Harmonic Distortion did the trick.
When amplifiers were all pretty much the same technology, then too or at least at first, lower distortion measurements did correlate to less coloration.
The problem began when high amounts of closed loop feedback were used, instead of 10 or 15dB of loop, with SS amplifiers they were 60 even 90+ dB of feedback. While that made static numbers that were very low, the measurements often departed from what one heard. Because of perceptual masking in our auditory system, the farther away from the fundamental the harmonic is, the easier it is at the same level to hear AND when listening to music which is harmonically structured, odd harmonics sound bad but even harmonics are often perceived as "richness". With natural sounds or industrial sound (none of which are harmonic) then even and odd harmonics can change the timbre. The problem with added feedback is that it lowers the low order distortion components but it generates new ones much higher up. If one examines our hearing sensitivity curve one see's that where ones sensitivity is greatest (around 3-4Khz) one finds that when a loudspeakers distortion components fall in that range they are also most audible relative to the fundamental.
At risk of sounding like a broken record, there are SO MANY things in addition to distortion that a generation loss test WILL RAPIDLY reveal the sonic infidelity of any component especially loudspeakers which by far ARE the weakest link. It doesn't tell you what to fix but by hearing the warts, it often shows where to look and often too, you can hear them afterwards listening directly. This has been invaluable at work especially early on.
Tom Danley
Danley Sound Labs