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In Reply to: Could you pls. clarify the point? posted by hexenboden on June 13, 2006 at 21:42:09:
I am addressing Soundmind about distortion measurement, since I have many 10's of thousands of dollars in test equipment (at least when it was new) and I use it virtually every day. How about the rest of you?
Follow Ups:
...I'm still unclear of your point. BTW if your point is that you have experience measuring equipment and still cannot correlate it to listening then I would ask why you have the measuring equipment in the first place. It is also possible that you personally may have trouble correlating but others don't. But in any event I am still unclear but interested in the point you are making.BTW I have the greatest respect of your ability to design and produce amps that deliver clean high power and measure (and sound) very good, and all at a reasonable price. That is the mark of great engineering, however you achieve it.
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I CAN correlate some of my measurements with subjective performance. However, I cannot measure FM distortion in amps with my test equipment, and you probably don't know why I should be concerned. One or two good measurements is not enough. Learn and grow.
Progress is always good, but it is also important to understand where progress is most needed. You design amplifiers for a living, I do something else. I probably know more about your profession, as an amateur, than you know about mine. Consumers are the final arbiters of taste, but they can never of course be as informed as professionals. Still, I hope I never said that a couple of measurements were enough, that would indeed be a mistake. Information is not necesarily equivalent to knowledge because it can frequently be misguided, even for the most enlightened designers. When you have a screwdriver you see screws everywhere... This is true of doctors, lawyers, engineers...you name it.FM distortion is nonlinear distortion of the signal in the time domain. I'm sure it's a worthwhile goal to reduce it. But how much more phase distortion is being induced by speakers and rooms? We must keep things in perspective. Measurements are useful for that too.
Right now as a consumer I am a lot more interested in progress (and the dissemination and commercial application of exisiting knowledge base instead of all this nonsense) in the fields of loudspeaker and room correction than amplification or digital.
Learn and grow indeed.
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I don't think that you understand FM distortion in linear amplifiers. I recommend that you read Barrie Gilbert's thesis on the subject.
nt
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There's a nice collection of articles on analog design here . I believe the article John is talking about is this one .
You are correct, Andy C, thanks for finding the links.
To the amazement of many here, I'm sure, ;-) this is the sort of article that excites audio designers and shows a previously unpredicted problem with negative feedback, except for Otala's early paper, of course, that never got into the AES Journal, because it was considered too controversial by the Lipshitz crowd. This is for real. Matti told me this, himself. That's why he dropped out of the AES publishing game.
To the amazement of many here, I'm sure, ;-) this is the sort of article that excites audio designers and shows a previously unpredicted problem with negative feedback, except for Otala's early paper, of course, that never got into the AES Journal, because it was considered too controversial by the Lipshitz crowd.Hi John,
Yes, I seem to remember a pretty long thread about the Gilbert paper on DIYA :-). I think your interpretation of this paper is somewhat different from mine though. The conclusion I reached was that the closed-loop distortion was as usual much less than the open-loop distortion. However, the open-loop amp had no AM-to-PM conversion, while such distortion was present in the closed-loop amp. It seems to me that referring to this as a "problem" depends on the assumption that the subjective effect of the AM-to-PM distortion is far worse than that of AM-to-AM. I'm not aware of any studies that have taken place regarding the relative audibility of AM-to-PM distortion compared to AM-to-AM when the magnitude of the distortion components are equal. It would be interesting to find out though. But regardless of our differing interpretations, I think we both agree that it's an interesting paper that's well worth spending time on.
And speaking of interesting publications, there's a classic text on the Volterra series that for a long time was out of print and unavailable except for very expensive used copies. It is now back in print again, with new material added. I didn't realize until recently that for time-invariant nonlinear systems, the input-output relationship was completely described by the Volterra series, which includes the linear system theory as a special case. Very thought-provoking stuff. The book is The Volterra and Wiener Theories of Nonlinear Systems .
HowdyI ordered it, it sounds like a fun read :)
-Ted
...with the thread title taken from the Beavis and Butthead quote, "It's 10 PM. Do you know where your weiner is?". But I figured people would think I was weird - and I didn't want them to know the truth! :-)
HowdyIt's been a while since I did any optimal Wiener filtering, but my wife seems to like...
-Ted
this still does not make it clear to me what the order of magnitude of this problem is in a well designed circuit.
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