Do all audio amplifiers really sound the same???

[anatech]

There are so many reasons why amplifiers sound different. Being an audio technician, I've measured many amplifiers over the years. I've had to accept that measurements don't tell everything about an amplifier. I've also made changes in the character of different amplifiers, even though the THD reading changed only slightly and within the range of uncertainty.

Why? I have some ideas, but nothing concrete. Just accept that this is true.

-Chris

[GRollins]

All the usual measurements are done with unvarying test signals. Music is rarely so accommodating. In fact, short of a synthesizer, or (arguably) a flute, there are no instruments that produce anything within shouting distance of a clean sine wave. Standardized dynamic tests are unheard of, yet music heavily relies on dynamics as part of its presentation. There is nothing whatsoever that will give you even the faintest glimmer of an idea as to how well a circuit images, despite that being one of the primary reasons for going from mono to stereo fifty years ago.
The list goes on and on...
Suffice it to say that there are people who either:
a) can't hear a difference and thus believe that no one else is able to
--or--
b) won't hear a difference because it would upend their world view. Note that this specifically includes the possibility of listener bias as described in the original post; i.e. they expect to hear no difference and so, mirable dictu, they hear no difference. Once their gurus have spoken, telling them there's nothing to hear and that anyone who says otherwise is delusional, then from that moment on, they are dead set against hearing anything.
One of a series of conceptual breakthroughs for me was the fact that people who lose their eyesight find that their hearing increases in acuity to compensate. I subsequently set out to educate my ears without losing my sight in the process. Some people do this by accident. Some people do it on purpose. The vast majority of people never do, either because it isn't important to them or it doesn't occur to them to do so...or because they actively don't want to.
The idea that people have no long term acoustic memory is laughable. You can instantly recognize someone by voice alone over a telephone--and that's a demonstrably low fidelity signal. It's easier still with a better signal.
There are a number of other threads here about this general sort of thing. You'll note that there are people who quickly identify themselves as being in the "there's nothing to hear" camp. But if you read enough posts by them, you'll find that many of them are in pursuit of multiple zeros to the right of the decimal point in THD measurement--far below anything that has been demonstrated to be relevant to human hearing for that distortion mechanism. If you then do something so brazen and ill-considered as to ask them why they pursue something that by their own belief system is unhearable, they will pour vituperation on your head and call you bad names. Their behavior alone will tell you all you need to know about them.

Grey

[KP11520]

The real challenge to that challenge is:

Ask the people who really believe that and or who concluded that study, "What amp do you have?"

If it isn't the cheapest amp that they can find that "functions properly" then they have been eating fecal matter for dinner and are still quite full of it. (I hope that isn't too over the top)

The funny part is when you ask them in another conversation a few days later what they have, they would display pride and brag about some fine piece of amplifier equipment they have and enjoy!

You just can't make this stuff up!

Regards//Keith

[anatech]

Hi Grey,
Well, multiple zeros to the left of the decimal point does not exclude an amplifier from the "sounds great" crowd.

The HP 3562A has a transient test mode. It's an amazing piece of hardware. Tone burst tests were standard at one time long ago. That would qualify as well.

Standardizing a test is trivially easy. Getting a group of people to agree what that standard will be is not. Even getting them to agree that a test is required would be unlikely.

Long term audio memory is short, proved. The fact that you can recognize a friends voice over the phone shows you the marvel of the human brain. What you are not doing is remembering precisely how they sound.

I suspect the listening test (which I agree with also) is more about recognizing the failures of a reproducing system. So it's the problems that you become aware of. Measurements and listening tests together are the only way to design a great amplifier.

-Chris

[bwaslo]

GRollins,

>you'll note that there are people who quickly identify themselves as being in the "there's nothing to hear" camp. But if you read enough posts by them, you'll find that many of them are in pursuit of multiple zeros to the right of the decimal point in THD measurement

I've seen this claim time and again, but have NEVER run into such a person in my reading or meetings with audio design engineers. Are there examples you can give of some?

I think you'll find that it is well accepted and established by the "there's nothing to hear camp" that harmonic distortion levels have virtually no relation at all to sound quality except perhaps at high extremes, or maybe when they increase as signal levels fall (such as in crossover distortion, virtually nonexistent it seems since maybe 1968). And other than by some unscrupulous marketeers several decades ago, there has been virtually no glorification of multiple zeros to the right of the decimal point as being significant to sound quality, at least that I've seen. Even Douglas Self's writings say that such numbers mean little, and that he pursues low distortion numbers more as an academic exercise and to assure that his amplifier designs would be "blameless" in this and other ways, should someone ever be able to demonstrate hearing differences -- and not that the low THD values have any known sound consequences. But I may be wrong about this, and would be interested in being corrected by some examples. I do get bugged by this claim, though, when it is counter to what I've read in journals or hear in discussions with people in the "there's nothing to hear" camp.

BTW, a death-dealing counter to the "there's nothing to hear" camp could be just one singe demonstration - with level matching and ruling-out of oddball amps (high output impedance, non-feedback, screwed up frequency response) of course - of a listener who is able to consistently tell, every time, common commercial amplifiers apart due to their sounds ALONE. It should be a very easy thing to disprove, shouldn't it? It would just take one repeatable demonstration. Why not show up at an AES convention or audio show and do that demonstration for the industry and the skeptics, put the issue to bed once and for all, and become famous?

Really, a lot of AES researchers would LOVE to have something like that to investigate and to find explanations for and to publish about. It is the stuff that could make major career reputations. These people don't resist such concepts, on the contrary it would be an AES members dream situation, but investigations like that can't happen without evidence. Provide the evidence, make everyone happy.

I won't say it can't be done. Just that until some evidence like that actually exists, there really doesn't seem to me to be much to talk about.

[KP11520]

BTW, Stop wasting time at that "other" forum! LOL

[GRollins]

Originally posted by anatech


Standardizing a test is trivially easy. Getting a group of people to agree what that standard will be is not. Even getting them to agree that a test is required would be unlikely.

Long term audio memory is short, proved. The fact that you can recognize a friends voice over the phone shows you the marvel of the human brain. What you are not doing is remembering precisely how they sound.

If it ain't agreed upon, it ain't a standard. I can come up with fifty tests, call them "standards" and wait for others to adopt them. I guarantee that I'll be waiting a long time.
You agree that you can identify voices, but you deny it's by sound. Now, that's a curious position to take. The last time I looked, voices were a purely audible phenomenon.

Originally posted by bwaslo


I've seen this claim time and again, but have NEVER run into such a person in my reading or meetings with audio design engineers. Are there examples you can give of some?

I think you'll find that it is well accepted and established by the "there's nothing to hear camp" that harmonic distortion levels have virtually no relation at all to sound quality except perhaps at high extremes, or maybe when they increase as signal levels fall (such as in crossover distortion, virtually nonexistent it seems since maybe 1968).

BTW, a death-dealing counter to the "there's nothing to hear" camp could be just one singe demonstration - with level matching and ruling-out of oddball amps (high output impedance, non-feedback, screwed up frequency response) of course - of a listener who is able to consistently tell, every time, common commercial amplifiers apart due to their sounds ALONE. It should be a very easy thing to disprove, shouldn't it? It would just take one repeatable demonstration. Why not show up at an AES convention or audio show and do that demonstration for the industry and the skeptics, put the issue to bed once and for all, and become famous?

Really, a lot of AES researchers would LOVE to have something like that to investigate and to find explanations for and to publish about. It is the stuff that could make major career reputations. These people don't resist such concepts, on the contrary it would be an AES members dream situation, but investigations like that can't happen without evidence. Provide the evidence, make everyone happy.

You really need to get out more. Start with some of the threads here at DIY. I believe there are long sections of this sort of thing in some of the threads pinned to the top of the Solid State Forum, although brush fires start up here and there, unpredictably. Who knows, possibly in this very thread...
You're postulating that the THD-is-everything crowd thinks in a linear, logical manner. Again, open the door, get outside, take a deep breath of fresh air. That was pretty much my entire point--that the position is inherently illogical and indefensible.
I'll be the first to defend someone's right to pursue this hobby as an intellectual exercise. I have no problem whatsoever with that. My disagreement with THD proponents begins when they then try to claim that less-than-audible THD is better. Better how? The best claim I've seen is from Bob Cordell that pursuit of lower THD "might" reduce other undiscovered distortions. To me, that claim is dubious. Others seem to find it convincing, however.
As for being a guinea pig...as I detailed recently in another thread, I did it for several years and got tired of it. No matter how many people you prove things to, there's always another one next week, and another the week after that, then another the week after that...all with this snotty "well you didn't prove it to me!" attitude. Screw it. I gave it up. Try it sometime before you urge it on someone else. It gets damned tiresome.
Want proof? Here you are, only a week or two after the last one, only we're not face to face and I'm not going to play along. Won't keep another from popping up next week, though.

Grey

[guitar_joe]

Yes they do sound the same.
(it's true. full stop)

Valve amplifiers will sound different because of their damping factor.

Mind you the fulfillment of this is that both amps are not clipping and have linear frequency respose etc. They both have to be good amps.

[Conrad Hoffman]

IMO, when people talk "measurements" they think of THD. THD is a wonderful tool for amplifier development, but it predicts absolutely nothing about the way an amp will sound. I simplify the whole thing down to "identical signals will sound identical". I don't waste ten seconds with those who don't accept this.

Now, get a good differential amplifier and compare the outputs of two amps (with the same speaker loads, etc), fed from the same signal. This is an old well established test. If you don't see significant differences (say, Carver's 70dB null), the amps will sound the same. If you do see differences, they may still sound the same, but claims to the contrary will carry far more weight.

The reality is that you'll always see significant differences. If you hunt them down, they'll be things like different distortion spectra, different phase shifts, and different hum and noise levels. You generally have to go to great lengths to get two amps to match. Even two supposedly identical channels will invariably be a bit different.

Thus I dispose of the "measurements aren't sensitive enough to show everything" rubbish. Those comments are only made by those who don't know how to measure. The problem is, we have very little correlation between any type of measurement, and some specific amplifier signature.

You can also subscribe to the Doug Self approach- if all errors are reduced below some arbitrary and very small number, the amplifiers must sound the same. The "blameless" amplifier. I'm of this belief, but I've never seen an amp where a differential test between input and output shows near zero error. Worse, I don't believe the most accurate and flawless amp necesarly sounds the best. You can often improve on the source by changing the response, the damping, or, in the case of vinyl, by contaminating it with spurious signals!

[xiphmont]

I deal with off-the-cuff 'sound quality assessments' that fall apart under real double-blind ABX testing every day. (I'm the creator of Ogg Vorbis-- so yes, I do mean 'every day').

I've met thousands of people who claim to be able to hear big differences between codecs, or amps, or headphones, etc and I can count on ten fingers the number who aren't deluding themselves. The placebo affect is incredbly strong. It's human nature.

I consider myself a very neutral individual. Very undeluded. I use blind, automated ABX testing on *myself*. My job is to know for sure, not to guess.

I'm not saying no one can hear the difference between two amps, or that there aren't audible differences. I'm saying that if you haven't done a double-blind ABX test under controlled conditions, you're talking out your *** and no one who knows better should take you seriously. Yes, it all comes down to listening. But even something like the low-level drone of a refrigerator a room over is enough to influence the results of these kinds of audiophile tests (bass pure-tone masking-- very insidious ;-)

I really doubt there are more than ten people here who are qualified to comment on any but the most obvious differences (hell, most of my own sound engineers will go days without noticing like a blown tweeter in a line array, and they're supposedly trained ears!). That includes me, if I haven't done such a controlled review of a particular piece of equipment.