When I get the spare time I'll go re-run some experiments. I know I've seen this more than once, but possibly at higher than audio frequencies?
At any rate, watch this space. I expect to get sufficient time right after I help my second kid through college: 2025 ought to be about right.
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" gives you just what it says. See details at http://www.wescottdesign.com/actfes/actfes.html
Hearing perception is a funny and tricky area. The type of distortion will factor into the amount you can stand or detect. I know that odd harmonics are less obnoxious, often dsirablee compared to even mode harmonics.. So, best have a look at the wave form and not just a % THD meter for this one. Non harmonics related would even be worse and more disrubing to human perception.
Best Regards,
Marc
I have indeed built distortion circuits to cause either odd or even type of harmonic distortion, primarily for use with electric guitars but also tested to a lesser extent on other audio signals such as mixed music and voice-only signals.
There is a lot of "conventional wisdom" that odd harmonic distortion is supposed to be worse than even harmonic distortion. What I have found is that lower order even is worse than lower order odd. (Mash down peaks of one side and "expand" the other side, or [lesser] do nothing but mash down peaks of one side, sounds to me worse than mashing down peaks in a symmetric manner.)
It appears to me that the intermodulation distortion is worse when harmonic distortion of a sinewave is towards the 2nd harmonic than when harmonic distortion is towards the 3rd.
As for audibility of distortion of a single frequency sinewave signal - to a fair extent audibility of harmonic distortion increases with harmonic number until the harmonics approach ultrasonic frequencies. Especially, distortion harmonics at frequencies below 2 KHz will be less audible than ones in or a little above the human hearing frequency response hump centered around 2.7-2.8 KHz. Also, when a distortion test is on audibility of specific harmonics from distortion of a pure sine wave as opposed to testing for audible intermodulation distortion, 2nd harmonic "passes-as-least-offensive".
2nd harmonic is same-note 1-octave-up from fundamental. Audibility of harmonics in a distortion test on a pure sine wave largely increases as harmonic number increases (as long as the harmonic is not ultrasonic or approaching ultrasonic), and also is less if it is a whole number of octaves from the fundamental, second-least if it is a "fifth" above (1.5 times higher in frequency) a whole number of octaves above the fundamental. However, when there is significant harmonic distortion towards 2nd harmonic as opposed to higher harmonics, ratio of audible offensiveness from IM distortion to ausible offensiveness of harmonic distortion appears to me to be maximized.- Don Klipstein ( snipped-for-privacy@misty.com)
I've finally seen a double-bind test on PBS:
But this write-up is just a teaser - they put two audiophiles and two engineers in a room, and behind the scenes, "randomly" switched between analog and digital (without interrupting the piece), and the listeners had two little paddles - "analog" and "digital", which they'd raise or lower, as they perceived the difference.
The result? The audiophiles guessed right 55% of the time, and the engineers guessed right 52% of the time.
Not much better than random chance! ;-)
Cheers! Rich
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