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Post by pknaz on May 6, 2018 22:27:27 GMT -5
I'd trust Gene's evaluation of amplifiers over the THX website every day of the week.
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Post by 405x5 on May 7, 2018 7:57:39 GMT -5
I'd trust Gene's evaluation of amplifiers over the THX website every day of the week. You got it! (Gene D. knows his stuff). Not at all to be arrogant, my own system for both movies 🎥 and music is one of the finest I’ve ever experienced, and not ONE component carries the “THX” certification, as I recall. That being said, running the thx audio tests on it would make any thx nut jump for joy. Bill
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mgbpuff
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Post by mgbpuff on May 7, 2018 7:59:10 GMT -5
Audioholics makes some good points. But we are talking about comparative tests under the same conditions for amplifiers. Could more tests have been done - surely. Could good results in some areas overcome worse results in other areas (we're talking about subjective listening results now) - surely. But a technical comparison is a technical comparison, maybe we need more to irreconcilably say that one amp is better than another. But I will always pay attention to a bad result in testing - period, especially when that testing is comparative and consistent between samples. And over design in one area does not necessarily compensate for poor design in another area. Good engineering is always a balance between value and results.
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Post by pknaz on May 7, 2018 9:39:39 GMT -5
But I will always pay attention to a bad result in testing - period, especially when that testing is comparative and consistent between samples. And over design in one area does not necessarily compensate for poor design in another area. Good engineering is always a balance between value and results. Even if the test was a meaningless test?
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mgbpuff
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Post by mgbpuff on May 7, 2018 10:00:29 GMT -5
But I will always pay attention to a bad result in testing - period, especially when that testing is comparative and consistent between samples. And over design in one area does not necessarily compensate for poor design in another area. Good engineering is always a balance between value and results. Even if the test was a meaningless test? You mean like your meaningless post?
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geebo
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Post by geebo on May 7, 2018 10:03:59 GMT -5
It was a valid question.
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Post by mgbpuff on May 7, 2018 10:05:09 GMT -5
O.K. sorry, which test was meaningless and why?
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Post by garbulky on May 7, 2018 10:27:44 GMT -5
IMD is not a meaningless test. Especially if it's showing -35 db distortion spikes. -35 db is audible in certain instances and not a good measurement. However, those were at 100 watts of power which you wouldn't always be listening at. If you assume all your music is at 0 db then you get an idea for 30 db. However your music is not a steady state and can vary between 15-40 db normally. So if you have a zero db peak, you may be having musical information at -30 db. If the music peak was recorded at say -10 db on peaks to prevent clipping, then you have to factor that in too because your -30 db musical content would be -40 db . Old 78 rpm records had about -40 db dynamic range which quickly got worse to -30 db. For comparison, CD's have about 90 db of dynamic range and cassettes about 50. Listening however will tell you how an amp is supposed to sound to you.
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Post by AudioHTIT on May 7, 2018 10:28:48 GMT -5
O.K. sorry, which test was meaningless and why? Right, I think the point is that we don’t know all the tests can best identify good or bad sounding amps, the more information we have the more informed our decisions will be. That said, since we don’t know if all of these tests are useful, distilling them down to a single score can be misleading. My take is that the tests may be useful, but we need more rational for the final score.
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Post by mgbpuff on May 7, 2018 10:49:42 GMT -5
I agree. I do not accept the 'single score', but I do accept the various tests, all of which are tied to some engineering attribute of the design. One test, almost always ignored because it is difficult to effect is showing amplifier performance into varying reactive loads instead of the common pure resistive load which is never encountered in the real world.
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Post by pknaz on May 7, 2018 11:03:24 GMT -5
From the article (linked above) that started this conversation: "Predicting the subjective effect of this objective behavior is probably an exercise in futility" and "I usually test an amplifier...by driving it at a high power with an equal mix of 19 and 20kHz tones, which is very much the worst case"
This is _NOT_ a real world scenario, and in the words of the author's own fingertips, would be an exercise in futility trying to make subjective sense of the objective test. This is what I meant by a "meaningless" test.
So the test is driving two sine waves, one at 19khz and one at 20khz and testing for IMD. Question: How long did it take for that IMD to propagate and reach the -30db point? Did it take 1,2,3,4,5,6 seconds before the IMD gradually increased in strength and peaked at -30db? If so, is this important in dynamic content? If not, does this behavior manifest with actual dynamic content or is it only reproducible under unrealistic lab tests?
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Post by pknaz on May 7, 2018 11:06:03 GMT -5
Additionally, if you read Gene's article from AudioHolics (also linked above) you'll see that many of the tests performed by THX are indeed meaningless and if amplifiers were designed to their (THX's) desired specifications would yield a very poor sounding amplifiers.
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Post by mgbpuff on May 7, 2018 11:14:59 GMT -5
An IMD test is a measurement of the linearity of an amplifier design, pure and simple. If the output contains other than the two fundamentals, then this show the degree of non-linearity. It is a continuous signal test. So what are you talking about? Dynamics and timed response has nothing to do with it.
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Post by pknaz on May 7, 2018 11:25:00 GMT -5
An IMD test is a measurement of the linearity of an amplifier design, pure and simple. If the output contains other than the two fundamentals, then this show the degree of non-linearity. It is a continuous signal test. So what are you talking about? Dynamics and timed response has nothing to do with it. Do you ever listen to continuous signals at 19khz and 20khz? Ever wonder why a test like this would even be performed? Kinda like rating power at only a 1khz input signal, with one channel driven, at 10% THD, do you know anyone who listens to content under that type of a scenario? To me, this screams of "hey, we need a test that makes some amplifiers look bad on paper" If the IMD doesn't manifest until after a period of time, than this test is meaningless If the IMD doesn't manifest under real world musical content, than this test is meaningless
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Post by pedrocols on May 7, 2018 11:37:48 GMT -5
So it seems that my tube amp will never be THX certified darn it.😒
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Post by garbulky on May 7, 2018 11:39:02 GMT -5
So it seems that my tube amp will never be THX certified darn it.😒 I don't think people should pursue thx certification. An amp does not require it to be a high performance amplifier.
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Post by mgbpuff on May 7, 2018 11:41:14 GMT -5
Additionally, if you read Gene's article from AudioHolics (also linked above) you'll see that many of the tests performed by THX are indeed meaningless and if amplifiers were designed to their (THX's) desired specifications would yield a very poor sounding amplifiers. I am not defending THX or their approach to ranking amplifiers. But I am defending sound engineering tests and their indisputable meaning. I did not read that Gene said a test was meaningless, but that THX's rankings based on the tests they chose to perform and tests that they chose not to perform gives a inaccurate estimate of the amplifiers overall performance.
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mgbpuff
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Post by mgbpuff on May 7, 2018 11:48:45 GMT -5
An IMD test is a measurement of the linearity of an amplifier design, pure and simple. If the output contains other than the two fundamentals, then this show the degree of non-linearity. It is a continuous signal test. So what are you talking about? Dynamics and timed response has nothing to do with it. Do you ever listen to continuous signals at 19khz and 20khz? Ever wonder why a test like this would even be performed? Kinda like rating power at only a 1khz input signal, with one channel driven, at 10% THD, do you know anyone who listens to content under that type of a scenario? To me, this screams of "hey, we need a test that makes some amplifiers look bad on paper" If the IMD doesn't manifest until after a period of time, than this test is meaningless If the IMD doesn't manifest under real world musical content, than this test is meaningless O.K. Now you are just showing your lack of understanding of both mathematics and engineering principles. Perhaps you should stick to subjective opinions which are valid even though they often defy explaination.
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Post by garbulky on May 7, 2018 11:52:02 GMT -5
Yep, THX did not make these tests up. They are common tests. The issue Audioholics had was with the ranking and the way they weighed certain measurements.
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Post by pknaz on May 7, 2018 12:02:06 GMT -5
Do you ever listen to continuous signals at 19khz and 20khz? Ever wonder why a test like this would even be performed? Kinda like rating power at only a 1khz input signal, with one channel driven, at 10% THD, do you know anyone who listens to content under that type of a scenario? To me, this screams of "hey, we need a test that makes some amplifiers look bad on paper" If the IMD doesn't manifest until after a period of time, than this test is meaningless If the IMD doesn't manifest under real world musical content, than this test is meaningless O.K. Now you are just showing your lack of understanding of both mathematics and engineering principles. Perhaps you should stick to subjective opinions which are valid even though they often defy explaination. That's a totally fare statement, I might not know as much as you do about mathematics or engineering principles. I'm happy to learn (seriously). What can this test teach us about how the amplifier's in question will sound or perform under a given real world scenario?
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