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In Reply to: I guess I'm just deaf posted by Feanor on July 6, 2012 at 10:55:37:
"I can't see what's off the graph, but I can see that the higher order harmonics are progressively lower in amplitude and that all are lower in amplitude with higher feedback. The HOs become signal-tracking noise: not good, but at some point so small as to be irrelevant"
It's easy enough to see the trend in the plots, no? It's clear there will be a 7th, 8th etc. etc. as the feedback increases because that is how the first 6 harmonics behaved. It won't stop there.
Ah, but how small is small and at what listening level?? Read Cheever for an idea about the audibility and then read the Pass paper to see how small small is. Hint, its a lot more complicated than those simple graphs you found.
No, 2nd order is masked and so is the third to some extent. The higher the level of the fundamental the wider the masking. Its because your hearing mechanism makes it's own distortion was it's all vibrating. Geddes and CHeever both show that its level dependent with masking the lowest at low levels, which means your ear is going to be most sensitive to extraneous distortion (like crossover distortion) at low levels. Crowhurst shows that a signal correlated and modulated "noise" floor is generated with high feedback that will mask low level signal information, ruining low level resolution. You can easily hear many db below a true noise floor, such as tape hiss, because it is not correlated with the signal.
Of course a very high level of 2nd order will tend to make things sound more open and brassy but as long as it doesn't exceed the masking threshold it should be inaudible. When you don't hear the distortion it will always sound more pleasant than audible distortion.
There is an interesting trial done by Keith Howard that you can find in Stereophile where he simulated distortion patterns with software modified music. He found that NO additional distortion sounded better than ANY additional distortion. However, he found that a monotonic or only even order harmonic pattern sounded LESS distorted than one with a lot of odd and high order harmonics. I suggest you read that one too.
Now, obviously if you can't hear what's wrong then live long and prosper but you found a reason to prefer your Class D. All I can say is that I haven't found one yet that I can live with (even though I have tried to live with three different ones and heard at least a dozen others at length) and they most definitely don't fit my criteria.
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Follow Ups
- RE: I guess I'm just deaf - morricab 15:07:49 07/06/12 (1)
- I'll reread Geddes, Cheever, et al. a few more times - Feanor 16:21:33 07/07/12 (0)
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