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Topic: ABX box (Read 7168 times) previous topic - next topic
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ABX box

http://www.avahifi.com/index.php?option=co...&Itemid=238[/url

Read the review here :

[url=http://www.dagogo.com/audio-by-van-alstine-abx-comparator-review-part-1-audio-store-wiring/2]http://www.dagogo.com/audio-by-van-alstine...-store-wiring/2

I'm seriously thinking of buying this unit in a few months so I can start doing some proper apples to apples comparisons between audio equipment. Seems like the perfect tool.

What do you guys think of it? Any criticisms/positives to share? It's a bit pricey at $1000, but if it saves me $$$ down the line plus make me more aware of the issues in perceptual testing and audible differences, makes me a better listener etc then I think it's worth forking money for.

I'm just trying to figure out how one would test an AVR using a power amp with preouts/vs no power amp in the chain, or if one needs two identical AVR's for the test.

ABX box

Reply #1 –
That is a lot to spend on a hobby.  Ever thought of building your own? 

As an aside, if you want to test power amps, a very easy way to do that would be to get a high end sound card (which perhaps you have anyway) and just record the output.  Then playback the files in foobar or another software ABX.

ABX box

Reply #2 –
Quote from: saratoga on
That is a lot to spend on a hobby.  Ever thought of building your own? 

As an aside, if you want to test power amps, a very easy way to do that would be to get a high end sound card (which perhaps you have anyway) and just record the output.  Then playback the files in foobar or another software ABX.


I'm not a technical guru. I've heard of the measuring outputs etc using software. But I've always wanted a proper ABX box. A lot of questions could be answered for me with this piece of kit, plus I can use it for testing upgrades in the future.

Unfortunately no one can loan this unit for me otherwise I would just loan the unit for a few weeks and test as many components as possible.  But I won't be so lucky.

ABX box

Reply #3 –
Quote from: Rich B on
http://www.avahifi.com/index.php?option=co...&Itemid=238[/url

Read the review here :

[url="http://www.dagogo.com/audio-by-van-alstine-abx-comparator-review-part-1-audio-store-wiring/2"]http://www.dagogo.com/audio-by-van-alstine...-store-wiring/2://http://www.avahifi.com/index.php?op...-store-wiring/2

I'm seriously thinking of buying this unit in a few months so I can start doing some proper apples to apples comparisons between audio equipment. Seems like the perfect tool.

What do you guys think of it? Any criticisms/positives to share? It's a bit pricey at $1000, but if it saves me $$$ down the line plus make me more aware of the issues in perceptual testing and audible differences, makes me a better listener etc then I think it's worth forking money for.

I'm just trying to figure out how one would test an AVR using a power amp with preouts/vs no power amp in the chain, or if one needs two identical AVR's for the test.


The article was an amusing trip down memory lane. AVA and the reviewer are well into reinventing the wheel, both as far as the comparator and also the listening test techniques that we invented almost 40 years ago. For example there is the issue of common speaker grounds - we never ever built an ABX relay box for power amp testing with common grounds, not even as prototypes.  We simply knew better.

Anybody who advises a DIY approach to this project IMO vastly underestimates the difficulty and costs of the project. At ca. $1K I don't know how they make a penny selling these.

ABX box

Reply #4 –
Quote from: Arnold B. Krueger on
Quote from: Rich B on
http://www.avahifi.com/index.php?option=co...&Itemid=238[/url

Read the review here :

[url="http://www.dagogo.com/audio-by-van-alstine-abx-comparator-review-part-1-audio-store-wiring/2"]http://www.dagogo.com/audio-by-van-alstine...-store-wiring/2://http://www.avahifi.com/index.php?op...-store-wiring/2://http://www.avahifi.com/index.php?op...-store-wiring/2

I'm seriously thinking of buying this unit in a few months so I can start doing some proper apples to apples comparisons between audio equipment. Seems like the perfect tool.

What do you guys think of it? Any criticisms/positives to share? It's a bit pricey at $1000, but if it saves me $$$ down the line plus make me more aware of the issues in perceptual testing and audible differences, makes me a better listener etc then I think it's worth forking money for.

I'm just trying to figure out how one would test an AVR using a power amp with preouts/vs no power amp in the chain, or if one needs two identical AVR's for the test.


The article was an amusing trip down memory lane. AVA and the reviewer are well into reinventing the wheel, both as far as the comparator and also the listening test techniques that we invented almost 40 years ago. For example there is the issue of common speaker grounds - we never ever built an ABX relay box for power amp testing with common grounds, not even as prototypes.  We simply knew better.

Anybody who advises a DIY approach to this project IMO vastly underestimates the difficulty and costs of the project. At ca. $1K I don't know how they make a penny selling these.


So you say this is a good piece of kit for testing audio gear?

ABX box

Reply #5 –
Quote from: Rich B on
Quote from: Arnold B. Krueger on
Quote from: Rich B on
http://www.avahifi.com/index.php?option=co...&Itemid=238[/url

Read the review here :

[url="http://www.dagogo.com/audio-by-van-alstine-abx-comparator-review-part-1-audio-store-wiring/2"]http://www.dagogo.com/audio-by-van-alstine...-store-wiring/2://http://www.avahifi.com/index.php?op...-store-wiring/2://http://www.avahifi.com/index.php?op...-store-wiring/2://http://www.avahifi.com/index.php?op...-store-wiring/2

I'm seriously thinking of buying this unit in a few months so I can start doing some proper apples to apples comparisons between audio equipment. Seems like the perfect tool.

What do you guys think of it? Any criticisms/positives to share? It's a bit pricey at $1000, but if it saves me $$$ down the line plus make me more aware of the issues in perceptual testing and audible differences, makes me a better listener etc then I think it's worth forking money for.

I'm just trying to figure out how one would test an AVR using a power amp with preouts/vs no power amp in the chain, or if one needs two identical AVR's for the test.


The article was an amusing trip down memory lane. AVA and the reviewer are well into reinventing the wheel, both as far as the comparator and also the listening test techniques that we invented almost 40 years ago. For example there is the issue of common speaker grounds - we never ever built an ABX relay box for power amp testing with common grounds, not even as prototypes.  We simply knew better.

Anybody who advises a DIY approach to this project IMO vastly underestimates the difficulty and costs of the project. At ca. $1K I don't know how they make a penny selling these.


So you say this is a good piece of kit for testing audio gear?


I would never advise the purchase of a component that I have as little actual useful info about as this one.  The first version with common grounded speaker level wiring was a bad joke. Hopefully they are learning...

One irony is that they could have asked any of the people who developed the original ABX comparator to advise, and they would probably do it gratis. This would have saved them some grief already. They are obviously very wise in their own wisdom, and so I wish them all the luck in the world!

ABX box

Reply #6 –
For comparing amps, receivers, AVRs (in stereo mode), integrated amps, bi-wiring, passive bi-amping, and speakers, this will do a lot of different kinds of A/B tests and it costs $986 dollars less:

http://www.amazon.com/OEM-Systems-IW-101-P...XY127ZN050765W8

Level matching can be achieved easily by downloading a test signal, for free, and getting your hands on a cheap voltmeter.

Once you establish that neither you nor your friends can hear a difference between say your Marantz AVR and some other receiver (or preamp/power amp combo), obviously both in true "Pure Direct" mode, you then can move on to using the A/B switch to compare DACs, CD players (if you can synchronize them), or any other line level devices using the volume knobs on the two receivers for level matching purposes:

DAC 1 ----> AVR 1 spkr. outs--------------\

                                                                                                .............................................................A/B  switch  -----------> Pair of Speakers

DAC 2 ----> AVR 2 spkr. outs--------------/


This alone will be enlightening but for scientific validity the test needs to be blinded so the person doing the listening can't be aware of which device is being listened to so they can't be subliminally biased one way or the other. One way to achieve this is to have one person test another so only the test conductor knows how the A/B switch is wired. This would be called a "single blind test".

If even the test conductor doesn't know how the switch box is wired, because it was done by a third party, then that's a "double blind test" or DBT. In lieu of that if the only test conductor on hand is out of sight to the listener and doesn't communicate with them during the test [worry about even just subtle body language cues and facial expressions] then for all intents and purposes the test is double blind.

Guessing the identities correctly just once or twice could just be dumb luck, so several trials need to be run in order to establish statistical significance. Getting, for example, more than 12 out of 16 trials correct would show good results that it most likely wasn't just dumb luck.

ABX box

Reply #7 –
Quote from: mzil on
For comparing speakers, amps, receivers, AVRs (in stereo mode), integrated amps, bi-wiring, passive bi-amping, and speakers, this will do a lot of different kinds of A/B tests and it costs $986 dollars less:

http://www.amazon.com/OEM-Systems-IW-101-P...XY127ZN050765W8

Level matching can be achieved easily by downloading a test signal, for free, and getting your hands on a cheap voltmeter.

Once you establish that neither you nor your friends can hear a difference between say your Marantz AVR and some other receiver (or preamp/power amp combo), obviously both in true "Pure Direct" mode, you then can move on to using the A/B switch to compare DACs, CD players (if you can synchronize them), or any other line level devices using the volume knobs on the two receivers for level matching purposes:

DAC 1 ----> AVR 1 --------------\

                                                                                                ................................................A/B  switch  -----------> Speakers

DAC 2 ----> AVR 2 --------------/




This alone will be enlightening but for scientific validity the test needs to be blinded so the person doing the listening can't be aware of which device is being listened to. One way to achieve this is to have one person test another so only the test conductor knows how the A/B switch is wired. This would be called a "single blind test".

If even the test conductor doesn't know how the switch box is wired, because it was done by a third party, then that's a "double blind test" or DBT. In lieu of that if the only test conductor on hand is out of sight to the listener and doesn't communicate with them during the test [worry about even just subtle body language cues and facial expressions] then for all intents and purposes the test is double blind.


Doesn't that switch need to be mounted into a wall or something? What's the point then of the ABX switch box? It doesn't make any sense to charge $999 if a cheap little switch can do the same job right?

ABX box

Reply #8 –
The switch won't know it isn't mounted in a wall. 

Quote
It doesn't make any sense to charge $999 if a cheap little switch can do the same job right?


My suggested version doesn't have a fancy wireless remote control. You've got a bunch of speaker wires running to the switch which rests on your lap as you listen. [You don't want to have to get up and walk across the room to switch. It should be quick and easy when you switch so it is right there on your lap.] Also with my version you have to take notes with pen & paper as to which trials were correct and which were incorrect. A computerized assistant doesn't keep score for you. Random assignment, usually done by the test conductor, for which device under test [DUT] will be wired as A and which will be B for each trial is done by the flip of a coin, literally.

Fancy ABX switch boxes have internal means to achieve A/B assignment randomization and electrical level matching for you. No volt meter, calibration tone, pen & paper, or coin is necessary.

ABX box

Reply #9 –
Quote from: Rich B on
What's the point then of the ABX switch box?


The big pay-off for ABX tests is the ability to make a fool of yourself with only you looking.

Anything that requires someone else to watch while you make a fool out of yourself is rather counter-productive.

ABX box

Reply #10 –
That AVA box looks pretty sweet! I like that it handles line-level devices, power amps and speakers. But it's a pricey way to find out that properly designed electronics really do sound pretty much the same.

ABX box

Reply #11 –
It does. My brother works in the audio field and is thinking of maybe splitting the costs for both of us to use.

Just a question on power amp level matching. If one is using an AVR and ensures the volume is set to a comfortable level, like say 65 dB as measured at the terminals, and one connects up a power amp using the preout function to the same AVR, would the volume levels change by adding the power amp at the same MV, measured at 65 dB (or rather measuring the voltage)?

ABX box

Reply #12 –
Quote from: Rich B on
If one is using an AVR and ensures the volume is set to a comfortable level, like say 65 dB as measured at the terminals, and one connects up a power amp using the preout function to the same AVR, would the volume levels change by adding the power amp at the same MV, measured at 65 dB (or rather measuring the voltage)?


I think you are talking about comparing the sound of an AVR by itself vs. the sound of an out board power amp getting its input from the same AVR's preamp outs. As long as you have a means of adjusting the level of the outboard amp to match that of the one inside the AVR [most power amps don't have their own level knobs, although some do] this will work.

As you make minor adjustment per song (or listener) with the AVR's master volume knob it simultaneously raises the volume coming out of its speaker output terminals as well as its preamp output terminals. You only need to calibrate the outboard amp to match that of the AVR's internal amp once, at the beginning of the test, and you then will be free to adjust the master volume of the receiver for all subsequent listening.

The level matching (don't forget to check both the L and R ch) is done by measuring the output AC voltage at the amps' speaker outs, say while reproducing a continuous 1 KHz tone.  You need not worry about what SPL it produces in the room at the distance you sit so all you need is an AC voltmeter. Some ABX switch boxes do level matching for you, others don't.

ABX box

Reply #13 –
Quote from: Rich B on
It does. My brother works in the audio field and is thinking of maybe splitting the costs for both of us to use.

Just a question on power amp level matching. If one is using an AVR and ensures the volume is set to a comfortable level, like say 65 dB as measured at the terminals, and one connects up a power amp using the preout function to the same AVR, would the volume levels change by adding the power amp at the same MV, measured at 65 dB (or rather measuring the voltage)?


The comparison appears to be of an external power amp as compared to the power amps in the AVR.

The two signal paths that are being compared are then:

(1) A:  AVR internal circuits including preamp  -> internal AVR power amp -> Speakers.   

This path's total gain is then:

    AVR internal circuits including preamp  gain (dB)
+ Internal AVR power amp (dB)
--------------------------
= Total gain in electronics path A


versus:

(2) B: AVR internal circuits including preamp -> External power amp -> Speakers

This path's total gain is then:

    AVR internal circuits including preamp  gain (dB)
+ External AVR power amp (dB)
--------------------------
= Total gain in electronics path B

The correct way to measure this gain this is to take a steady test tone and measure the difference in voltage between the common source of the test tone with the output of each of the two paths which is exposed at the speaker terminals.

The correct way to match this gain this is to take the  steady test tone and measure the difference in the output of each of the two paths which is again exposed at the speaker terminals.

The exposure is that the gain of the external power amp and the gain of the AVR internal power amp are different. Usually good power amps have their own volume controls, so hopefully the external power amp has more gain, and its gain can be reduced to match that of the AVR internal power amp using its volume controls.

ABX box

Reply #14 –
Quote from: Arnold B. Krueger link=msg=0 date=
The exposure is that the gain of the external power amp and the gain of the AVR internal power amp are different. Usually good power amps have their own volume controls, so hopefully the external power amp has more gain, and its gain can be reduced to match that of the AVR internal power amp using its volume controls.


I understand that it's good practice to ensure the volumes are properly matched. I'm not disputing that.

Most consumer power amps that I've seen don't include volume controls. I just wanted to know if, in my scenario, if one were using an AVR, set to particular volume, and only changing the power amp, via preamp outs, would it be necessary to match levels.

I'm asking because many people I know have bought outboard power amps with their AVR's claiming [insert subjective waffle] vs just using their AVR. So I wanted to know if in these cases, simply changing the power amp itself without doing anything would alter the volume levels at any particular MV.

So if we use an MV of 50 (for 75 dB or what have you). Connect a power amp up. Without changing the MV of 50, would the SPL levels be higher? Because that may explain why people go hysterical after upgrading to a power amp. If only the volume levels changed, it may explain a lot.


ABX box

Reply #15 –
Quote from: Rich B on
Quote from: Arnold B. Krueger link=msg=0 date=
The exposure is that the gain of the external power amp and the gain of the AVR internal power amp are different. Usually good power amps have their own volume controls, so hopefully the external power amp has more gain, and its gain can be reduced to match that of the AVR internal power amp using its volume controls.


I understand that it's good practice to ensure the volumes are properly matched. I'm not disputing that.

Most consumer power amps that I've seen don't include volume controls. I just wanted to know if, in my scenario, if one were using an AVR, set to particular volume, and only changing the power amp, via preamp outs, would it be necessary to match levels.



Matching levels isn't nice or good practice. It is one of a short list of keys to having a valid test.

The whole list is:

(1) matching levels

(2) Time-synching the music being used to do the comparison. IOW simply but aggressively using the identical same music to listen to both items being compared.

(3) Concealing any information about relevant differences so that the listener only knows what he hears

(4) Letting the listener control the test and switch whenever he wants to. Making the switchover short enough that the most sensitive kind of human memory can be used.

(5) Actually do a test - that is compare the UUT to a fixed, repeatable, reliable, relevant reference.  The preferred universal reference is the proverbial short, straight piece of wire.

Make sure that the following remains constant for the duration of at least every test:

(a) Listening to the identical same music.

(b) Listening via the identical same system.

© Listening in the identical same room.

(d) The identical same listener doing listening.

(e) The listener is seated in the identical same place.

This all seems like utter simple common sense to me, but almost every audiophile and reviewer listening evaluation seems to blow at least one critical point.

ABX box

Reply #16 –
Arnold, could you please answer this for me :

Quote
Most consumer power amps that I've seen don't include volume controls. I just wanted to know if, in my scenario, if one were using an AVR, set to particular volume, and only changing the power amp, via preamp outs, would it be necessary to match levels.

ABX box

Reply #17 –
Quote from: Rich B on
Arnold, could you please answer this for me :

Quote
Most consumer power amps that I've seen don't include volume controls. I just wanted to know if, in my scenario, if one were using an AVR, set to particular volume, and only changing the power amp, via preamp outs, would it be necessary to match levels.



Of course!

Level matching is an absolute non-negtiable requirement for a valid test.  Necessary but not sufficient.

If you don't match levels at the speaker terminals +/- 0.1 dB 20-20 KHz, don't bother doing any other testing.

I still keep external volume controls (just 10K potentiometers in boxes with jacks) around for level matching when I need to.

ABX box

Reply #18 –
Quote from: Arnold B. Krueger on
Quote from: Rich B on
Arnold, could you please answer this for me :

Quote
Most consumer power amps that I've seen don't include volume controls. I just wanted to know if, in my scenario, if one were using an AVR, set to particular volume, and only changing the power amp, via preamp outs, would it be necessary to match levels.



Of course!

Level matching is an absolute non-negtiable requirement for a valid test.  Necessary but not sufficient.

If you don't match levels at the speaker terminals +/- 0.1 dB 20-20 KHz, don't bother doing any other testing.

I still keep external volume controls (just 10K potentiometers in boxes with jacks) around for level matching when I need to.


You're the expert on these matters, but if I were to test an AVR sans power amp, and an AVR with power amp, I would just test two identical AVR's (one without power amp) and one using power amp voltage-matched at the terminals.

It's unlikely I would have two identical AVR's handy to test, but that's how I would do it with my low level of knowledge. Short of that, I'm lost on how I would compare a single AVR with power amp attached, and the same AVR without power amp attached, matched in level.

ABX box

Reply #19 –
Quote from: Arnold B. Krueger on
Quote from: Rich B on
Arnold, could you please answer this for me :

Quote
Most consumer power amps that I've seen don't include volume controls. I just wanted to know if, in my scenario, if one were using an AVR, set to particular volume, and only changing the power amp, via preamp outs, would it be necessary to match levels.



Of course!

Level matching is an absolute non-negtiable requirement for a valid test.  Necessary but not sufficient.

If you don't match levels at the speaker terminals +/- 0.1 dB 20-20 KHz, don't bother doing any other testing.

I still keep external volume controls (just 10K potentiometers in boxes with jacks) around for level matching when I need to.


Ok, thanks.

ABX box

Reply #20 –
Rich, you have your AVR setup with its volume knob in the primitive and as far as I'm concerned wrong mode, for this day and age. I can tell this by the way you describe volume settings on it:

Quote
So if we use an MV of 50 (for 75 dB or what have you).


You have it on "Absolute" mode, which is actually a bit of a misnomer, and instead you really should change it to "Relative". The advantages are numerous:

- gives the user a meaningful visual indication of volume changes in a well defined, universally agreed upon standard: decibels [or dB for short], so changes can be discussed meaningfully with other people

- once calibrated by Audyssey (which you should do) gives the user a good indication of the SPL they are achieving when presented with any defined signal level, even up to a full scale signal [0dBFS]. That is, if you set your volume to level "X", and then  a year later listen to your friend's different Audyssey calibrated AVR in a different room, at a different seating distance, with different speakers, also at volume indication setting of "X", you are hearing it at (roughly) the same SPL. [Unfortunatly I can only say "roughly" because the system isn't accurate enough to achieve proper, precise level matching to the tenth of a dB by this means.]

As an analogy, think of it being like you now have a thermometer with gradations marked on a scale of 1-10 [or 1-11, 1-100, or even better (to understand this), A through Z, doesn't really matter] whereas everyone else has thermometers marked in Fahrenheit [or if you prefer, Celsius]. If a friend asks you, "Boy, it just dropped below freezing at my house. Is it below freezing where you live too?" You can only answer: "I don't know. My thermometer says it is in the middle of its range and I don't even know what the top and the bottom of it's range means exactly. All I know is the temperature at my house reads 'M' and I can't even safely assume other people with thermometers that read 'M' are experiencing the same temperature as I am".

Here's the button sequence to convert to the proper Relative volume indications:

Menu > manual setup> option setup> volume control> alter volume display to "relative".

Once you have done this, when a person says, "I like to listen to my rock and roll CDs and DVDs at about -35 dB volume on my Audyssey [or for that matter THX] calibrated receiver", it has a specific meaning to other people and they can replicate the conditions themselves on their Audyssey or THX receivers.

I'm pretty sure this defacto standard is also used by current Yamaha and many other major brands which come with mic calibration technology as well.

What is this other power amp you are contemplating comparing to your AVR, by the way?

ABX box

Reply #21 –
Quote from: Rich B on
Short of that, I'm lost on how I would compare a single AVR with power amp attached, and the same AVR without power amp attached, matched in level.


Can you get your hands on a source device with variable output level? If so I can tell you how to do it.

Such devices might include:

- TV set playing any incoming source, including an optical disc player

- a computer playing whatever you like

- a laptop/notebook playing whatever you like

- a smartphone, cell phone, or portable music player that has music stored in it

- an optical disc player, such as my Oppo, which has a variable output level option

ABX box

Reply #22 –
Quote from: mzil on
Rich, you have your AVR setup with its volume knob in the primitive and as far as I'm concerned wrong mode, for this day and age. I can tell this by the way you describe volume settings on it

You have it on "Absolute" mode, which is actually a bit of a misnomer, and instead you really should change it to "Relative". The advantages are numerous:

- gives the user a meaningful visual indication of volume changes in a well defined, universally agreed upon standard: decibels [or dB for short], so changes can be discussed meaningfully with other people

- once calibrated by Audyssey (which you should do) gives the user a good indication of the SPL they are achieving when presented with any defined signal level, even up to a full scale signal [0dBFS]. That is, if you set your volume to level "X", and then  a year later listen to your friend's different Audyssey calibrated AVR in a different room, at a different seating distance, with different speakers, also at volume indication setting of "X", you are hearing it at (roughly) the same SPL. [Unfortunatly I can only say "roughly" because the system isn't accurate enough to achieve proper, precise level matching to the tenth of a dB by this means.]

As an analogy, think of it being like you now have a thermometer with gradations marked on a scale of 1-10 [or 1-11, 1-100, or even better (to understand this), A through Z, doesn't really matter] whereas everyone else has thermometers marked in Fahrenheit [or if you prefer, Celsius]. If a friend asks you, "Boy, it just dropped below freezing at my house. Is it below freezing where you live too?" You can only answer: "I don't know. My thermometer says it is in the middle of its range and I don't even know what the top and the bottom of it's range means exactly. All I know is the temperature at my house reads 'M' and I can't even safely assume other people with thermometers that read 'M' are experiencing the same temperature as I am".

Here's the button sequence to convert to the proper Relative volume indications:

Menu > manual setup> option setup> volume control> alter volume display to "relative".

Once you have done this, when a person says, "I like to listen to my rock and roll CDs and DVDs at about -35 dB volume on my Audyssey [or for that matter THX] calibrated receiver", it has a specific meaning to other people and they can replicate the conditions themselves on their Audyssey or THX receivers.

I'm pretty sure this defacto standard is also used by current Yamaha and many other major brands which come with mic calibration technology as well.

What is this other power amp you are contemplating comparing to your AVR, by the way?


Hi Mzil. My Marantz AVR has been set in the relative mode. I'm aware of the absolute and relative settings. When I said an MV of 50, I also referenced an SPL figure to put it into context. 75 dB. It doesn't really matter what the MV number is, so long as the SPL that I want can been obtained (using the trim controls).

I listen at -15 MV on average (0 dB is calibrated 75 dB as per SPL meter at my seat). I don't typically like using Audyssey. I've never had good experience with it, even following the step by step methods over at AVS regarding mic positioning. Regarding the power amp, I'm just making a general inquiry. No specific power amp in particular.