John Curl's Blowtorch preamplifier part III

[mmerrill99]

Originally Posted by vacuphile

Yet, blind testing apparently never has become a great succes in automobile development either. There must be a lesson in this for audio!

But it's not all measurements/simulations in F1 car development - drivers, test drive & give feedback about car handling, etc.

[DF96]

Originally Posted by mmerrill99

But I've never seen anybody on here suggest that if you are negatively biased towards there being an audible difference in amplifiers (for instance, could be DACs, cables, whatever) then you are likely not a suitable listener for ABX testing of amplifiers, as you will be biased towards a null result - have you?

I may be wrong, but I suspect that you have suggested it. Certainly someone has. You talk as though you are not 'on here' but merely talking to people 'on here' (from an imagined position of superiority?).

What if people don't know or admit to their negative bias, how do you discover it?

Everyone has prior assumptions, 'positive' or 'negative'. A good test will help overcome them, unless they are so strong that they are forced to reject the test results.

Have you got some acceptable evidence that the results from 'sighted' listening ala how Hoyt stated are more wrong than the results from ABX listening?

Nobody has evidence which you will accept, because your bias is so strong.

Perhaps but there can be other physical factors besides bit patterns that may not be the same between listening sessions & could result in audible differences.

Do I detect some wriggling and squirming in the light of an inconvenient test result? Differences clearly 'heard' between bit-identical files are somehow not a false positive? Differences between item A (seeing A) and item A (seeing B) are not a false positive?
Surely this is not bias at work?

[PMA]

Originally Posted by gpapag

In terms of level balancing, you have done a great job. Plus the amp does not change the dynamic range of the signal (<0.2dB)

Is this one?

George

Thank you for posting your analysis, George. I will post mine as well, but it is good to have yours as an independent one.

However, I do not think it is a technical point or real test parameters that are attacked. It is the ABX itself, by those who do not like the protocol. I understand it, but if I have a choice between technically well performed ABX and a sighted test, I would vote for the ABX. Further, where is the proof that the parameters like level equalization within 0.2dB were fulfilled in the sighted test? That would be my question to the oponnents.

[PMA]

Originally Posted by Jakob2

Below 0.3 dB it gets more and more difficult and that´s usually the region where imE all listeners only notice the sound difference but not the level difference as such.

So using level difference at different niveaus even allows to monitor the effect of training.

As you know well, level difference is not only a result of "volume control setting", but it is however a quite complex result of frequency response and non-linearities as well. As a non-linearity in my DUT goes up to 1%, it affects the "level" as well, should it be a peak level, peak rms, avg rms and min/max rms. Please check the file stats I have shown in my previous post.

However, we still have a "null" ABX result, so we should not blame the result to a "poor" 0.2dB level matching.

[scottjoplin]

Seems to me the bottom line is, it's probably easier to sell your overpriced, shiny gear if you can come up with a good enough reason to legitimise sighted tests.

[Jakob2]

Originally Posted by PMA

As you know well, level difference is not only a result of "volume control setting", but it is however a quite complex result of frequency response and non-linearities as well. As a non-linearity in my DUT goes up to 1%, it affects the "level" as well, should it be a peak level, peak rms, avg rms and min/max rms. Please check the file stats I have shown in my previous post.

A positive control is a difference (known to be detectable) presented within a test setup to check if everything works as intended.

So, the answer to your question is simple, use material where such difficulties does not exist; for example take the "wire sample" and use it to present the mentioned level difference as a positive control.

[TNT]

Originally Posted by mmerrill99

But it's not all measurements/simulations in F1 car development - drivers, test drive & give feedback about car handling, etc.

It will soon be over...

YouTube

//

[mmerrill99]

Originally Posted by DF96

I may be wrong, but I suspect that you have suggested it. Certainly someone has. You talk as though you are not 'on here' but merely talking to people 'on here' (from an imagined position of superiority?).

Semantics, semantics - you know what I mean but choose to take a different meaning - I wonder should you be accused of "putting words in my mouth"?

Everyone has prior assumptions, 'positive' or 'negative'. A good test will help overcome them, unless they are so strong that they are forced to reject the test results.

Yes, you make my point - so let's try to use a "good test" by using some controls that internally validate the test procedure - simple, really

Nobody has evidence which you will accept, because your bias is so strong.

Try me with some evidence rather than some spurious argument. I have a feeling that you are really being self-revealing in this as I seem to remember that you rejected Jakob2's evidence about the insensitivity of ABX testing - am I wrong?

Do I detect some wriggling and squirming in the light of an inconvenient test result? Differences clearly 'heard' between bit-identical files are somehow not a false positive? Differences between item A (seeing A) and item A (seeing B) are not a false positive?
Surely this is not bias at work?

Of course there can be false positives in sighted listening, I stated that many times already but you fail to admit that ABX testing is prone to false negatives despite evidence & many here still use ABX test results (of any quality) to try to claim that a sighted listening report is a false positive. Fact of the matter is you are trying to elevate some unknown quality listening 'test' to a status that is unwarranted & unscientific & trying to use it to negate sighted listening

[PMA]

Originally Posted by Jakob2

A positive control is a difference (known to be detectable) presented within a test setup to check if everything works as intended.

So, the answer to your question is simple, use material where such difficulties does not exist; for example take the "wire sample" and use it to present the mentioned level difference as a positive control.

Oh, I see. In a test setup itself, the level difference is verified to be in order of 0.01dB. Less than 0.1dB. Now, please tell me why you ask, if there has been no positive ABX protocol yet?. In case there are positive results, I understand there is a reason of being suspicious to the level difference only. I still have a strong feeling there is a reluctance to the ABX method itself, rather than to real technical issues. Seems to me as a substitute issue.

Now, to your test with black boxes. I have read your description carefully. Please tell me, you, who say that 16 attempts in ABX is not enough and you consider it statistically unimportant, how valid is your 5/5 result in a semi-sighted, semi-blind test as you have described.

[Jakob2]

Originally Posted by PMA

<snip>
Further, where is the proof that the parameters like level equalization within 0.2dB were fulfilled in the sighted test? That would be my question to the oponnents.

There must exist (still after all these years ) some profund misunderstandings.
The most outspoken advocats for strict level equality were indeed the proponents of "blind" listening tests (in which was back then usually the ABX comparator was used). Level difference should be below 0.1 dB (iirc in the Clark amplifier challenge hhoyt mentioned the target was below 0.05 dB).

Despite the "partisan" attribution there is good reason for best possible level equality especially when using fast/easy switching between the DUTs.

In sighted listening the most common routine (i´ve seen used) is/was to reduce the level to zero before changing the DUT and after the exchange to step the level up until listeners think it´s almost the same loudness as before.

I have done some tests with (obviously unbiased listeners due to the results) humans to monitor what level difference using this routine will be actually result and found (by using music) that the difference was in the region of 0.3 dB - 0.8 dB, but randomly distributed between the two DUTs.

As written quite often before, in this case the level difference presents an additional "noise" that might make detecting the real difference (if any exists) more difficult.

If listeners are biased (under sighted conditions) it obviously can happen that the level difference will not be randomly distributed but in favour of one of the DUTs, so that should be monitored/ruled out.