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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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In Reply to: Good points on harmonic spectrum. posted by Tony Montana on October 3, 2003 at 12:44:19:
Tony:There is evidence that the audibility of harmonics depends on their order. In general:
The higher the order, the more it is audible.
Odd order harmonics are perceived as more "unpleasant" than even order.So, a system may sound great with 0.1% THD if it's all second harmonic, while another may sound edgy and hard with 0.01% that's all 5th and 7th. The threshold of audibility for 7th-harmonic distortion is apparently extremely low -- we really don't like it.
It's intuitively obvious when you consider that the 2nd harmonic is simply one octave higher than the signal (same with the 4th and 8th), whereas the 7th is completely unrelated to the fundamental (musically-speaking).
There are many people (myself included) who believe that the shape of the envelope of the harmonic is relevant. A monotonically decreasing harmonic series seems to have the least audible impact. In other words, no harmonic should be higher in level than the one below it.
This is one of the reasons for the debate over feedback. One of the effects of feedback is that it lowers the total magnitude of the distortion, but shifts it to higher orders. Take the two circuits I described above: A simple circuit with no feedback might be all 2nd, and applying feedback could shift it up to mostly 4th-8th, albeit at a lower level. The second circuit will probably sound brighter and harder, even though the total distortion might be 20dB lower.
Of course, on the flip side some would say that the first circuit has lots of "euphonic" 2nd order distortion, therefore the second is more accurate. I know which I would rather listen to.....
Peter
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Follow Ups
- It varies wildly, depending on the harmonic - Commuteman 14:45:54 10/03/03 (1)
- Thanks Jon and Commuteman for the comments. - Tony Montana 13:54:44 10/08/03 (0)
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