Blind Testing Amps

ddude003

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@RichB Please don't classify all Tube PreAmplifiers/Amplifiers as non-linear... A triode tube is about as linear as they get... Tubed PreAmplifiers/Amplifiers have several types of architectures each with its own tradeoffs, just like SolidState PreAmplifiers/Amplifiers...
 
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What is linear vs non-linear... educate me on the difference and benefits of each.
 

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Oh boy... an hour is precious these days.

Interesting that Earl shrugs his shoulders at why people like tube amps, since he says it can't be the added distortion with it being masked.

Interesting... Earl says frequency response changes as the speakers heat up... and it takes more than a sweep to heat them up. Perhaps listen to music for 15 minutes, then measure them. I don't know that I've ever compared it.

Stopping at the water break... gotta go cut grass.
 
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BenToronto

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Just how "high" is the output impedance? As long as damping factor taller than maybe 5, should sound the same as yet higher. (Motional feedback amps have output impedance like -2 Ohm, if I recall correctly.)

Not a very complete list of amps tested with ABX box. I bought most of my amps at the Salvation Army store (good name when you think about it, eh). How come you didn't test anything from the 1980's?

Kidding, but I am not kidding about any good amp from 1980s sounding the same as any today.
 

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No one disputes this, so a bit of Red Herring. None of your speakers listed would have such a well know, accepted issue.


Link??
I have high output impedance tube amps easily heard. Again, not a disputed issue at all and nothing equivalent to your claim.

If attempting a valid test method you would need to provide that there is a case where a different amp could be identified. Such amps exist, it is not irrational to take this approach. It is always possible the the test could never yield a possible.

There are many dogmas.

- Rich
 
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RichB

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No one disputes this, so a bit of Red Herring. None of your speakers listed would have such a well know, accepted issue.

Link??
I have high output impedance tube amps easily heard. Again, not a disputed issue at all and nothing equivalent to your claim.

I write very openly about my listening session and my feelings about it.
I am not sure why you find this threatening.

Even with the caveat that amps operating within their range, have no way of telling what that range is. Most amps with similar topology should behave similarly but it is possible to implement protection mechanism like soft clipping for maximum reliability.

This is non a simplistic view where absolutes are determined with couple of measurements.
No one disputes that amplifier design can differ in this are.
Link to all of the being the same???
These type of posts get silly fast.

BTW, I did not see this attitude toward reviews observations made about the AHB2 so must assume there is something else at play.

- Rich
 

RichB

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@RichB Please don't classify all Tube PreAmplifiers/Amplifiers as non-linear... A triode tube is about as linear as they get... Tubed PreAmplifiers/Amplifiers have several types of architectures each with its own tradeoffs, just like SolidState PreAmplifiers/Amplifiers...

OK.
Here is the $150,000 (per pair) VAC Statement 452 iQ Musicbloc mono/stereo power amplifier measurements:
VAC Statement 452 iQ Musicbloc mono/stereo power amplifier Measurements | Stereophile.com
420VAC452fig1.jpg



The are clearly swings driving the simulated speaker of 1 dB. However, it is also worth noting the drop in response with load, down almost 1 dB into 4 Ohms and about 2.5 dB into 2 Ohms.

I am not saying anything about SS to SS amp comparisons only that you have to measure them. In theory, a ABX test could be auditioned and found not audibly identifiable. What would be the proper conclusion from such a test? That the amplifier is indistiquishable for a well behaved SS amp. That would not be my first thought :)

- Rich
 

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Not a very complete list of amps tested with ABX box. I bought most of my amps at the Salvation Army store (good name when you think about it, eh). How come you didn't test anything from the 1980's?

Kidding, but I am not kidding about any good amp from 1980s sounding the same as any today.
You know you are welcome to setup a test of however many amps you want to include and get however many people involved as you'd like. As for us... having the number of guys arrange to drive or fly in to my home and stay 4-6 days, and arrange to get this many amps to my home at one time, was anything but simple to make happen. We did what we could do, but of course for some it might not ever be enough. :whistling:

As for 1980 amps sounding the same as any today... I would have no reservations to say that amps from the 1970's would sound the same as amps today, provided everything is kept within the amp's capabilities. I can't tell you why we did not try to source one, but it doesn't matter, as it's over and done with... excuses are just that and serve no purpose other than to perhaps pamper someone's curiosity.
 

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Correct, but again, there is nothing to suggest any of those amps, with proper gain structure, would produce audible hiss at LP unless the sensitivity of the speaker is very high, say >98db....extremely rare in the HiFi market where as noted, 99% are more like your Revels. None would produce hiss then unless malfunctioning. Your claims were not for hiss/noise giveaway though, which of course is a well known metric. You are claiming actual sound differences into a non-pathological load, not overdriving the amps.
That is an extraordinary claim. Thus, N-Ray, Cold Fusion, etc methods scrutiny warranted.


That would be cool, especially in the context of intended use. There are real blind test experts there, like JJ and SIY.
Beware of return policy though it seems...


That's more than my belief. :)

cheers

On second, thought, I don't understand the need to consult ABX experts to discuss if a speaker switch can be used to switch speakers. This is make and break switch so there is no ground issue and if polarity is reversed on one amp, it does destroy an amplifier. That's a good feature.

Clearly, the MiniDSP SHD can used to digitally-level match for amp comparisson. That is superior matching analog attenuation with .1 dB resolution.

It could be made blind but requires an operator out of view. This is not an all-in-one tool for blind or sighted testing, but from a performance perspective, superior and measured at ASR.

- Rich
 

AJ Soundfield

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On second, thought, I don't understand the need to consult ABX experts
They aren't "ABX" experts, they are valid blind test experts, ABX being one of many valid, as is triangle, MUSHRA, etc.
In the same way your sighted AB is one of many totally invalid methods.
I'm not suggesting you consult with them if your sole desire is completely invalid testing results. Only valid. Those, they (SIY, JJ, DDF, etc) can help you with.
I think we understand now why you're not bringing it up over there, :)

cheers
 

AJ Soundfield

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Clearly, the MiniDSP SHD can used to digitally-level match for amp comparisson. That is superior matching analog attenuation with .1 dB resolution.
It could be made blind but requires an operator out of view. This is not an all-in-one tool for blind or sighted testing, but from a performance perspective, superior and measured at ASR.
A SHD is in no way superior or even comparable to an AVA ABX for randomized DUT blind testing. Anyone remotely familiar with blind testing and subsequent statistical analysis would understand this,
 

Mike-48

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This is not directly related but this was Jon Iverson's take on blind testing (which I am in favor of):
A Different Take on Blind Audio Tests (twit.tv)

Right. I worked in a statistical field for 30+ years, and the most common errors in methodology are not technical ones, but in interpreting results. As Iverson correctly points out, what is being tested here is the entire system, which includes not just the amps in question but the specific users' ears and brains. He also is correct that detecting audible differences can be learned -- Harmon, e.g., has an audio course to teach that. A null result in an audio AB or ABX test (as noted) says only that under the test circumstances, those listeners could not detect a difference. That does not imply that there is no difference of importance -- though I'd posit that differences people hear easily (e.g., in speakers) are probably more important ones.

Iverson also makes a great point about needing time to hear differences. If that wasn't true, why would manufacturers make boom-sizzle speakers that sound good long enough to be bought, but become tiresome over time? On a subtler level, how many of us have not developed sensitivity to coloration in a component we had used happily for a long while? The urge to upgrade is not all audiophila nervosa.

I do believe in buying well-engineered equipment. I also believe that audio quality goes beyond measurements, not in some mystical way, but just because music is so complex and varied, as is our hearing, and our taste.

Mike (still only 1/2-way through Iverson's interview)
 

Sonnie

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The only problem I have with Jon is a massive amount of non-proven hypotheticals. It sounds good if you take everything he says as factual and proven, but it's not... or at least I've not seen it published anywhere.

A lot of this discussion has stemmed from the AHB2 amps (it came from that thread)... interesting what Benchmark's chief designer says about listening and measuring, very interesting articles: https://benchmarkmedia.com/blogs/application_notes

The first paragraph of his Listening vs. Measuring article caught my attention right away.

At Benchmark, listening is the final exam that determines if a design passes from engineering to production. When all of the measurements show that a product is working flawlessly, we spend time listening for issues that may not have shown up on the test station. If we hear something, we go back and figure out how to measure what we heard. We then add this test to our arsenal of measurements.

Even though measurements show no flaws, they still listen, and if they identify something different, they figure out a way to measure what they heard. This is truly amazing to me. Take a look at the products they make, and take a look a the specs, and look at the unbelievably crazy good specs verified by numerous people taking measurements with the best gear available to do so. Then imagine that these guys at Benchmark STILL listen for differences and THEN figure out a way to measure those differences. They firmly believe that if they hear a difference, they should be able to measure it.

I can't see where he would not be as qualified as any other in the industry. So pick your poison... there are a LOT of different schools of thought out there that in some ways contradict each other.
 

Mike-48

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Here is the $150,000 (per pair) VAC Statement 452 iQ Musicbloc mono/stereo power amplifier measurements:

Right again. Note the tube amp's clearly audible (1.5 dB) variations in frequency response into a reactive load. Compare that to a really good SS amp, the Benchmark AHB2, at about $3000. The variation is down to about 0.2 dB:

1115BAHB2fig01.jpg


Such difference should be audible to a careful, trained listener. If not, there would be something wrong with the test conditions.
 

Mike-48

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Even though measurements show no flaws, they still listen, and if they identify something different, they figure out a way to measure what they heard. This is truly amazing to me.
Agreed! Probably that's why the AHB2 has been so positively received. And, I'd add, that is the way to make progress in audio . . . to find a way to measure what's heard.

Iverson is not wrong about one thing. A null test in an AB test is impossible to translate into a finding of no objective difference. That is a truth of statistical tests generally: you can't prove a difference doesn't exist, only that your methods are not sensitive enough to find it.
 

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A null result in an audio AB or ABX test (as noted) says only that under the test circumstances, those listeners could not detect a difference.
Correct and of course, anyone familiar with controlled testing knows this. The opposite of course, a positive result, would certainly warrant further investigation. But not if ascertained under completely invalid conditions.
Btw, both Iverson and Fremers reputed positive results would be proof positive FOR blind tests working just fine.

Iverson also makes a great point about needing time to hear differences.
There are no time limits to blind tests, unlike echoidc memory.

I also believe that audio quality goes beyond measurements, not in some mystical way, but just because music is so complex and varied, as is our hearing, and our taste.
Audio/soundwaves quality doesn't go beyond audio/soundwaves measurement. Otherwise it can't be designed into and manufactured with. Unless magical :) . Audio "experience" under typical, uncontrolled conditions certainly does. But that has little to do with soundwaves, as I have linked numerous times before.

cheers,
 

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Oops wrong graph
 

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Iverson is not wrong about one thing. A null test in an AB test is impossible to translate into a finding of no objective difference. That is a truth of statistical tests generally: you can't prove a difference doesn't exist, only that your methods are not sensitive enough to find it.

I say bologna all day long... as I've still not seen anyone publish any sort of proof of this. Again... not saying there are no differences, but there has been no published proof of it that I have read thus far. To say that blind testing is invalid just because no one on the face of the earth can disprove it, is silly. Besides that... what is any amp company going to advertise for those that claim they can hear a difference? What is it that they advertise? "Our amp was identified by 1 person out of 100 in ABX double blind testing as being ???". Is it really going to be significant enough to make the amp sell? The only improvement is that it can be more neutral than the other amp, unless it is coloring the sound in some way... or does not have inaudible specs.
 

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In theory, a ABX test could be auditioned and found not audibly identifiable. What would be the proper conclusion from such a test?
You mean conclusion from your theory, not test. There was no test.
 

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Agreed! Probably that's why the AHB2 has been so positively received. And, I'd add, that is the way to make progress in audio . . . to find a way to measure what's heard.
Actually, publishing these sort of "findings" for peer review and replication is how progress is made,
I've haven't seen any.

Iverson is not wrong about one thing. A null test in an AB test is impossible to translate into a finding of no objective difference. That is a truth of statistical tests generally: you can't prove a difference doesn't exist, only that your methods are not sensitive enough to find it.
"It"? Established how?
 

RichB

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The only problem I have with Jon is a massive amount of non-proven hypotheticals. It sounds good if you take everything he says as factual and proven, but it's not... or at least I've not seen it published anywhere.

A lot of this discussion has stemmed from the AHB2 amps (it came from that thread)... interesting what Benchmark's chief designer says about listening and measuring, very interesting articles: https://benchmarkmedia.com/blogs/application_notes

The first paragraph of his Listening vs. Measuring article caught my attention right away.

At Benchmark, listening is the final exam that determines if a design passes from engineering to production. When all of the measurements show that a product is working flawlessly, we spend time listening for issues that may not have shown up on the test station. If we hear something, we go back and figure out how to measure what we heard. We then add this test to our arsenal of measurements.

Even though measurements show no flaws, they still listen, and if they identify something different, they figure out a way to measure what they heard. This is truly amazing to me. Take a look at the products they make, and take a look a the specs, and look at the unbelievably crazy good specs verified by numerous people taking measurements with the best gear available to do so. Then imagine that these guys at Benchmark STILL listen for differences and THEN figure out a way to measure those differences. They firmly believe that if they hear a difference, they should be able to measure it.

I can't see where he would not be as qualified as any other in the industry. So pick your poison... there are a LOT of different schools of thought out there that in some ways contradict each other.

It is amazing, but clearly Benchmark knows that the ultimately their battery of tests in not enough to ship a design.
They listen to these amps with a variety of loads.
Perhaps, they have found in listening, unexpected results. Once observed, a test was made that uncovered the source.
Observation, leads to analysis that leads to correction that ultimately completes with observation.

I believe that everything that can be heard can be measured, but not everything heard is necessarily measured.
Amplifier manufacturers are not guaranteed to measure the same, some are more comprehensive than others.
Manufacturers (the good ones) perform all standard measurements found in reviews, they know the tests.

Simply reciting, that everything can be heard is measured is simplistic.
Obviously, amps have different design goals and will measure to assure that they achieve them.
This is the nature of product development.
There are many "objectivists" in audio that have made up their minds and can be every bit as intransigent as the pure subjectivist.

Personally, I want more and better measurements.
The "working within their limits" is near meaningless statement that cannot be determined.
Many amps wont accurately display when they are clipping, soft clipping, current limiting a transient, etc.
An AVR amp has a measurement goals but also, perhaps more important, reliability goals.
It is critical that these products operate and sound good to the target audience.

Those leaning objectivist (as I am), still need to probe the conditions of the listening session.
There are weaknesses to all and any findings have limitations and may not provide meaningful efficacy for all systems.

- Rich
 
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RichB

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You know you are welcome to setup a test of however many amps you want to include and get however many people involved as you'd like. As for us... having the number of guys arrange to drive or fly in to my home and stay 4-6 days, and arrange to get this many amps to my home at one time, was anything but simple to make happen. We did what we could do, but of course for some it might not ever be enough. :whistling:

This was great!
It is a serious undertaking to setup test with multiple participants and I applaud anyone who does it. I don't think I would ever have the energy to undertake something like that. Wow.

- Rich
 
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RichB

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They aren't "ABX" experts, they are valid blind test experts, ABX being one of many valid, as is triangle, MUSHRA, etc.
In the same way your sighted AB is one of many totally invalid methods.
I'm not suggesting you consult with them if your sole desire is completely invalid testing results. Only valid. Those, they (SIY, JJ, DDF, etc) can help you with.
I think we understand now why you're not bringing it up over there, :)

cheers

Quick switching has known benefits and clearly an aspect of blind.
Did I say it was blind? NO.
Neither did I every imply that this was better than a blind.
This is a dispute without merit.
It is not unreadable to question the limits of test equipment and seek performance specifications. This should not be interpreted as goring ones ox.

Instantaneous switching is a lot better, then multi-day or even one minute change over.
The notion that comparisson cannot be made in home is ridiculous, all honest audio people do this, some admit it.

Over where? I posted this information on ASR, I am not a coward as you infer.
I do not snipe from my keyboard, nor do I impugn. ;)
These techniques are not productive, detracting from respectful discussion.

- Rich
 
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