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How do you reliably ABX equipment that needs to be disconnected, and how can TOS #8 be satisfied in such situations?
Arnold B. Kruege...
post Feb 6 2011, 14:06
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QUOTE (knutinh @ Dec 29 2010, 08:45) *
QUOTE (saratoga @ Dec 29 2010, 06:21) *
Thats probably fine from a blindness perspective, however unless the differences are quite large I think the long time it'll take to switch samples will make it impossible for you to detect a difference. So your test will be blind, but also probably give you a negative result smile.gif


A valid concern. Switch-over times significantly in excess of 1 second cut listener sensitivity to actual differences in tests we've done to find out the effects of switchover delays.

QUOTE
If one cannot remember the audible impression from sound gadget #1 over a time-span of 5 minutes well enough to reliably compare it to sound gadget #2, what does that say about the benefit I would get in my home stereo if I bought one instead of the other? After all, if I purchase a new amplifier, I do not expect to rapidly switch back and forth between it and the older one for the products lifetime.


This is a critical point. Very few people are able to achieve switchover times that are signfiicantly less than 5 seconds. But, a 5 second or longer switch over delay pretty well destroys listener sensitivity to small differences.

We built hardware switching equipment that reduced switchover dealys to less than a quarter of a second and this boosted our sensitivity to small differences that were actually audible. The technique is described in Clark's JAES paper, and I can asnwer questions about it because I developed it over a period of several years.

The bottom line is that most golden ear A/B tests are inherently *not sensitive* to small differences, should they actually exist, because of their lengthy switchover times.


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Arnold B. Kruege...
post Nov 29 2014, 18:36
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QUOTE (LocrianGroove @ Dec 29 2010, 19:11) *
I think 0.1 dB accuracy would be hard to attain by adjusting output levels, but I could compensate by changing RG tags. Thanks for the feedback.


Back in the day I and others did it whenever we wanted to.

We played test tones at various frequencies and then measured the voltage across the speakers and adjusted gain as needed.

We had analog attenuators that were designed to be reasonably easy to set levels within 0.1 dB, and used voltmeters to confirm. 0.1 dB is about the same as 1%.

The volume controls on modern equipment usually has 0.5 steps and those are way too coarse - often easy to ABX sucessfully.
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amirm
post Nov 29 2014, 18:59
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QUOTE (BearcatSandor @ Nov 1 2010, 22:44) *
QUOTE (saratoga @ Nov 1 2010, 21:22) *
Get a really good ADC and record both outputs, then ABX the WAVs.

I've been thinking about this. Unless i am misunderstanding something that i've always taken for granted, that is that the inputs of an amp are electrically different than the speaker outputs, how could you do this with an amp? I assumed you were only speaking of source components.

I'm not an electrical engineer.

You have wisdom though as if you were though smile.gif. Hooking up the output of a power amplifier to the input of a sound card will assuredly damage your sound card. Possibility of smoke pouring out is quite high. And if the input of your sound card is DC coupled, such damage may easily extend to the rest of your computer. The amplifier output has voltage swings that are far, far in excess of the line level input of your sound card. It will cook it and cook it good if you do this.

To do this properly you need to build a dummy load and a voltage divider that feeds the input of the sound card only the very low amplitude excursions is expects (relative to the amplifier).

There are more serious problems with some amplifier designs. Some class D ones will have one leg of the speaker at half the mains supply voltage (e.g. 60 volts in US). Connecting just that leg of amp to your sound card's ground pin on the sound card will cause catastrophic damage to your sound card/PC, and seriously damage the amp too if it does not have a protection circuit.

No way should you attempt this without proper engineering knowledge.


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Arnold B. Kruege...
post Nov 30 2014, 10:39
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QUOTE (amirm @ Nov 29 2014, 12:59) *
QUOTE (BearcatSandor @ Nov 1 2010, 22:44) *
QUOTE (saratoga @ Nov 1 2010, 21:22) *
Get a really good ADC and record both outputs, then ABX the WAVs.

I've been thinking about this. Unless i am misunderstanding something that i've always taken for granted, that is that the inputs of an amp are electrically different than the speaker outputs, how could you do this with an amp? I assumed you were only speaking of source components.

I'm not an electrical engineer.

You have wisdom though as if you were though smile.gif. Hooking up the output of a power amplifier to the input of a sound card will assuredly damage your sound card. Possibility of smoke pouring out is quite high. And if the input of your sound card is DC coupled, such damage may easily extend to the rest of your computer. The amplifier output has voltage swings that are far, far in excess of the line level input of your sound card. It will cook it and cook it good if you do this.

To do this properly you need to build a dummy load and a voltage divider that feeds the input of the sound card only the very low amplitude excursions is expects (relative to the amplifier).

There are more serious problems with some amplifier designs. Some class D ones will have one leg of the speaker at half the mains supply voltage (e.g. 60 volts in US). Connecting just that leg of amp to your sound card's ground pin on the sound card will cause catastrophic damage to your sound card/PC, and seriously damage the amp too if it does not have a protection circuit.

No way should you attempt this without proper engineering knowledge.


All true, and there are similar cautions related to switching one pair of speakers between the outputs of two amplifiers.

Some switches momentarily connect the two sources to each other during the switch-over process. I'd do some careful testing before hooking amplifiers to anything but passive speakers.

That all said I've had good success hooking audio interfaces up to power amp outputs after taking adequate precautions.

The better audio interfaces have enough less distortion and noise than all but the very very best amplifiers that they can be the basis of sensitive reliable measurements and also make recordings that can be very revealing of audible distortion in certain power amplifiers.

When the amplifiers are so good that audio interfaces can't be used to reveal their distortion, their distortion is orders of magnitude less than audibility.
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amirm
post Nov 30 2014, 18:08
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QUOTE (Arnold B. Krueger @ Nov 30 2014, 01:39) *
The better audio interfaces have enough less distortion and noise than all but the very very best amplifiers that they can be the basis of sensitive reliable measurements and also make recordings that can be very revealing of audible distortion in certain power amplifiers.

When the amplifiers are so good that audio interfaces can't be used to reveal their distortion, their distortion is orders of magnitude less than audibility.

Hi Arny. I don't recall ever seeing the results of any such testing. Do you have some files that you can share and what outcomes you are using to base that conclusion?


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Amir
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Arnold B. Kruege...
post Dec 1 2014, 13:03
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QUOTE (amirm @ Nov 30 2014, 12:08) *
QUOTE (Arnold B. Krueger @ Nov 30 2014, 01:39) *
The better audio interfaces have enough less distortion and noise than all but the very very best amplifiers that they can be the basis of sensitive reliable measurements and also make recordings that can be very revealing of audible distortion in certain power amplifiers.

When the amplifiers are so good that audio interfaces can't be used to reveal their distortion, their distortion is orders of magnitude less than audibility.


Hi Arny. I don't recall ever seeing the results of any such testing. Do you have some files that you can share and what outcomes you are using to base that conclusion?


Of course the above makes no sense Amir because you've raked me over the coals at least once before for using audio interfaces to test amps.


Well, I'm still in Connecticut till Wednesday and the Wayback machine is sequestering my old www.pcavtech.com web site from me, so this is the best I can do right now:

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amirm
post Dec 2 2014, 16:50
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Arny, I thought we were talking about listening tests and not measurements.

I am asking for listening test results for the method suggested: using a sound card to capture the signal to the speaker. Do you or anyone else who suggested this has any listening test data and specifically captured files to share? I am starting to think no one does.


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Amir
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Arnold B. Kruege...
post Dec 3 2014, 15:50
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QUOTE (amirm @ Dec 2 2014, 10:50) *
Arny, I thought we were talking about listening tests and not measurements.

I am asking for listening test results for the method suggested: using a sound card to capture the signal to the speaker. Do you or anyone else who suggested this has any listening test data and specifically captured files to share? I am starting to think no one does.


I hesitate to post these files as I am sure that they will be abused. There will be many posts of dubious integrity claiming to have "pased" them, I fear. But in that search for honest men...

https://www.dropbox.com/s/4yovwg2u5cj35ki/U...0tests.zip?dl=0

The key to filenames is as follows:

USA850_010w_cop01_timpanids

USA850 = power amplifier model - QSC USA 850

010w = power levels - 10 watts peak

cop01 = number of passes through UUT, in this case 1 pass

timpanids - program material type - Timpani
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amirm
post Dec 3 2014, 15:59
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QUOTE (Arnold B. Krueger @ Dec 3 2014, 06:50) *
I hesitate to post these files as I am sure that they will be abused. There will be many posts of dubious integrity claiming to have "pased" them, I fear. But in that search for honest men...

Thank you Arny. This is great. I downloaded and will listen later.

How did you do yourself on them?


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Amir
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Arnold B. Kruege...
post Dec 3 2014, 21:10
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QUOTE (amirm @ Dec 3 2014, 09:59) *
QUOTE (Arnold B. Krueger @ Dec 3 2014, 06:50) *
I hesitate to post these files as I am sure that they will be abused. There will be many posts of dubious integrity claiming to have "pased" them, I fear. But in that search for honest men...

Thank you Arny. This is great. I downloaded and will listen later.

How did you do yourself on them?


I aced some, ended up with random guessing on others, as did the other listeners.
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