Blind Listening Tests & Amplifiers

[nw_avphile]

Originally posted by ashok
Good amplifier designs are supposed to mean that they are practically transparent - that they add almost nothing to the signal they amplify. . .
So most amps which sound very different must be adding something of their own ( different frequency response, distortion spectra , output impedance etc). Some will be liked and some will not.

That's what the null test is for! It tells you both subjectively (if you listen to it) and objectively (if you measure it) EXACTLY how the amplifier is changing, adding to, taking away from, distorting or otherwise altering the input signal.

I agree with some of what you say. But once you reduce the input/output difference to the level of most any well designed amplifier, it becomes relatively easy to argue the amplifier distortions are NO LONGER AUDIBLE. The blind tests support this argument. Amplifiers that can be distinguished in a blind test tend to do poorly on the null test, those that cannot be distinguished, do well.

I suggested folks who can produce a known attenuation in their system play music at a comfortable level (a level you would use to listen for subtle differences in a piece of audio gear). Then reduce the music by say 60 or 70db and see how loud the result is. You may find you can no longer hear it from your listening position! If you can hear it, it's so incredibly faint, it's easily masked by even the slightest background noise, let alone the original signal.

So again, it stretches common sense and credibility for someone to claim they can hear something that's 60 or 70db below the signal--or at least they can hear it well enough for it to account for the vast differences people profess to hear between amplifiers.

The thing to keep in mind here is the things I'm suggested can be verified with a minimum of special equipment. This stuff isn't philosophical, hypothetical or intangible. It's real and verifiable. Conversely, those who disagree, are asking others to make a leap of faith and simply believe in what cannot be objectively verified.

[Peter Daniel]

Originally posted by nw_avphile



So far, nobody in this thread has provided any credible objections as to why null testing isn't valid. The closest I've heard is it also identifies inaudible distortions, which is true, but that doesn't invalidate it as a test of amplifier transparency. It's almost as if some of you want to believe there's some other magic "ingredient" to amplifier sound that wouldn't be accounted for by comparing the input to the output in real-world operating conditions. How else can you explain your views? If a tree falls in the woods when nobody is around does it make any noise?

Like I said, it comes down to art and science. For those of you who want amplifiers that "artfully" distort the sound, or prefer to use very costly components because they make *you* think it sounds better, that's fine. Many people prefer art over science. But I also ask that you don't try to discredit the rest of us who prefer more objective proof that one amplifier, or capacitor or whatever, sounds and/or measures better than another one.

This whole thread reminds me very much of a Bose thread. Although it didn't provide any valid conclusion it was very entertaining. The person who started the current thread seems to be very enthusistic about his point of view, yet to me it seems like we are talking here about apples and oranges. If I can use a good analogy I could compare it to a discussion between two types of people. One type have never had sex and they just talk about it using their imagination and try to describe it the best way they feel approporiate. Second type, had sex and they know what it's all about. There is no way they can pass their experience and sensations they were subjected to, to the group of the people who never had it.

Originally posted by nw_avphile
Finally, I have a question for everyone...

How many of you think you could tell a $300 mainstream (Asian made) integrated amplifier from high-end separates costing at least ten times as much like those from say Krell or Bryston in a blind test in your own home (your speakers, your music, etc.)?

Who really cares about that kind of a challenge and what does it really prove?

Even if I wouldn't be able to hear the difference between both amps in a DBT, it won't suddenly make me able to enjoy the sound of a $300 integrated amp

[fdegrove]

Hi,

Conversely, those who disagree, are asking others to make a leap of faith and simply believe in what cannot be objectively verified.

Are we?

Seems the other way around to me.

Cheers,

[Peter Daniel]

There is another side to the whole subject. Some of you may be right claiming that properly measuring and capable with a load amps should sound the same and you can actually predict their sound by conducting so called null test. I can accept that and I can see your point.

Yet for me such equipment is useless, since it's not design to create real music. It's like a copy machine, which will never create nice picture but only passes out what it's fed.

For me a good amp is like a good violin. I don't care if it's 100% accurate if the price I'm paying for that is lifeless product, the music which doesn't have body and soul. For me the amplifier has to create "flesh and blood" experience, it has to provide a lot of technicolor and drama (I'm not using my words here, but I like them). Only then I can really enjoy the amp. Otherwise, what is keeping me from listening to a basic system that came with my computer?

[nw_avphile]

Originally posted by Peter Daniel
The person who started the current thread seems to be very enthusistic about his point of view, yet to me it seems like we are comparing here apples to oranges. If I can use a good analogy I could compare it to a discussion between two types of people. One type have never had sex and they just talk about it using their imagination and try to describe it the best way they feel approporiate. Second type, had sex and they know what it's all about.

Well... as I've explained more than once, I've done the high-end audio thing and was on the other side of the fence for quite a while. I still consider myself an audiophile and have spent five figures on my "hobby" so it's not like I'm sitting at home with an Emerson stereo from Wal-Mart.

I designed and built a high-end dual mono, fully symmetrical power amp. It has regulated higher voltage rails for the gain and driver stages, hand matched parts, audiophile WonderCaps, Roederstein metal film resistors, dual huge torroids, soft recovery rectifiers, fancy gold connectors, multiple current mirrors, Kimber Kable, silver solder, etc, etc. It's a great amp, was a labor of love, and it's still going strong. But I also built it before I discovered the reality of blind testing. So please don't insinuate I'm a DIY or audiophile virgin.

[Peter Daniel]

Originally posted by nw_avphile

Well... as I've explained more than once, I've done the high-end audio thing and was on the other side of the fence for quite a while. I still consider myself an audiophile and have spent five figures on my "hobby" so it's not like I'm sitting at home with an Emerson stereo from Wal-Mart.

I designed and built a high-end dual mono, fully symmetrical power amp. It has regulated higher voltage rails for the gain and driver stages, hand matched parts, audiophile WonderCaps, Roederstein metal film resistors, dual huge torroids, soft recovery rectifiers, fancy gold connectors, multiple current mirrors, Kimber Kable, silver solder, etc, etc. It's a great amp, was a labor of love, and it's still going strong. But I also built it before I discovered the reality of blind testing. So please don't insinuate I'm a DIY or audiophile virgin.

Even if you went to the other side of a fence it either wasn't long enough or you picked the wrong spot. If, as you say, you spend five figures on your hobby, you wouldn't be mentioning the above parts. This is the basic stuff and not high end. Just as an example, I'm using $28 resistors in my amps and $75 caps, and I still didn't justify to spend 2 grands for the interconnects. And I don't even dream about considering myself as a hard core audiophile yet.

[fdegrove]

Hi,

I designed and built a high-end dual mono, fully symmetrical power amp. It has regulated higher voltage rails for the gain and driver stages, hand matched parts, audiophile WonderCaps, Roederstein metal film resistors, dual huge torroids, soft recovery rectifiers, fancy gold connectors, multiple current mirrors, Kimber Kable, silver solder, etc, etc. It's a great amp, was a labor of love, and it's still going strong.

And to what "low-end" gear would that set-up "null" I wonder?

Cheers,

[nw_avphile]

Originally posted by fdegrove
I think it was the great Peter Walker of Quad fame who said that all good amplifiers should sound the same.

Note: good and should.Very subjective terms, are they not?

Yes they are, but not being able to tell the difference between a $300 Japanese piece of mainstream consumer electronics and audiophile gear costing more than ten times as much isn't subjective at all. It's black and white. Either you can hear enough of a difference to do better than you would just guessing, or you can't.

Likewise, measuring the difference between the input and output of an amplifier and finding if it's at a level that's way below audibility is also objective.

I don't care what components you start with to do your comparisons. If you you can tell them apart in a proper blind test, then you have my vote there's an audible difference between them. Pick the one you like better and go from there.

But if you can't tell them apart, I argue they really don't have any significant audible difference (to the people listening at least).

[fdegrove]

Hi,

I don't care what components you start with to do your comparisons. If you you can tell them apart in a proper blind test, then you have my vote there's an audible difference between them. Pick the one you like better and go from there.

Like it or not the difference is still there.

I am not blind, I don't listen blind either and to me the entire issue is moot in that I notice time and time again that even across the globe and independently from eachother people notice the same:

In casu: people like Fred Dieckmann, Peter Daniel, Eric (Mr.FeedacK), countless others worldwide and myself are in concordance about quite a few, yet seemingly, unmeasured/uncorrelated phenomena.

It is sometimes freaky, spooky, to see someone across the globe confirm your own experiments...and that is exactly how I hope the net will accellerate development in audio.

Other than that null us out if you like, we know better than that.

Cheers,

/Frankie Pedantie.

[Steve Eddy]

Originally posted by fdegrove
I see, that's why you spun a thread on that ad nauseam?
Oh, and now it's phase? Not polarity?

The previous thread was about polarity and how it is not synonymous with phase. Apparently you still seem to be laboring under the notion that phase and polarity are synonymous.

This discussion is about phase, as it has to do with time delays.

The proof.

<i>High-Frequency Phase Response Specifications--Useful or Misleading? Jensen, Deane, JAES, Vol. 36, Issue 12, p. 968, preprint no. 2398.</i>

Yes, and that is either ahead in time or lagging in time...so what's your point?

I'm simply distinguishing between frequency-dependent delays and frequency-independent delays.

Again, what's it going to be? Phase or polarity? And if absolute polarity doesn't matter anymore than I'm either death or stone cold dead.

It's phase when it's phase and it's polarity when it's polarity. Absolute polarity and absolute phase are not one and the same. Though since you can't seem to distinguish the difference between polarity and phase, I can understand your confusion.

Isn't that what we call phase shifts?

Yes. And as long as frequency versus phase is a linear function, group delay, which is the first derivative of this function, will be flat and all frequencies will be delayed by the same amount. And the shape of the waveform will not be altered.

Wow...that's new to me.
Imperfect splitters he? Glad you caught up but it seems you still haven't caught all of it.
Just discovered different behaviour in different order filters, or what?

It's not simply a matter of the order of the filter. Two second order filters with the same cutoff frequency may have vastly different group delays.

Take a look at the group delay of a second order Bessel compared to say a second order Chebychev.

Not that you would want that.

Well, techincally speaking, you would want that. A flatter (i.e. better) group delay that is. The flatter the group delay, the more linear the system.

No, it's frequency dependent delays that you don't want.

And it's group delay that shows you how frequency dependent the delays are.

And phase accuracy IS major importanto!!!

You're missing the point.

The point is, simply looking at phase data doesn't impart any useful information.

Here, let me give you an example from the preprint I cited above.

<center>
<img src="http://www.q-audio.com/images/phase1.jpg">
</center>

This is a phase plot of two networks, A and B.

Considering just the phase data, one might conclude that network B was worse than network A. However network B actually has a much flatter group delay plot. Meaning that network B is the more linear of the two and alters the signal the least.

So again, forget about phase. What matters is group delay.

se