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Topic: How to level-match electronics (Read 8031 times) previous topic - next topic
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How to level-match electronics

So I've been reading some of the older threads and have learned about the importance of level-matching.

Now I would like to learn how to do it. Are there any videos or tutorials that show how to level-match electronics, the right way? I looked on Youtube and I noticed no videos to be found.

Thing is, IME, if people want to try this out and want to learn it needs to be shown. Since this forum is filled with knowledgable people who do this kind of thing for breakfast, would anyone be willing to show how it is done, and post a video on youtube?


How to level-match electronics

Reply #1
I attempted to give a brief tutorial on how I did it when I conducted a blind test of my "expert listener" audiophile friend and actually started a thread on it at the AVS forum. Within moments of posting it a carnivore from the high-end industry swooped down to intentionally attack and sidetrack the discussion because having the lay public learn what counts and what doesn't in audio, by testing it out themselves, is completely at odds with their marketing strategy of "Trust us, we are more experienced than you and have had training to hear things you wouldn't necessarily notice until you buy an expensive, top-notch system."

New topic. Things become a bit more complex and controversial if you are attempting to level match things that fundamentally have markedly different frequency responses, such as speakers and headphones. Say for example one speaker has a stronger level of bass than the other one being tested. Do you level match them using pink noise? Do you level match them at 1 kHz? Do you instead level match them at 500Hz? Do you use a narrow band of noise centered where the ear is most sensitive, around 3.5 to 4 kHz? Do you use A-weighting when you conduct any of these level matches? You will get very different results depending one which exact method you use when the products have certain frequency response deviations between them.

I'm of the mind that one should accept that level matching things like speakers and headphones is so tricky, problematic, and questionable, that "fair, level matched comparisons" simply can't be done. This doesn't stop researchers at Harmon, etc. from publishing papers where they say "and we level matched" and nobody but me seems to blink an eye. "Our trained listeners preferred speaker A over B due to tonal balance. We level matched the two so that couldn't have influenced their selection" Um. now wait a minute. If you level matched them using A-weighting and speaker A has a broad peak at 4kHz that speaker B doesn't, I'd hardly describe the two as being "level matched" using that method because the very concept of what is "correct in all situations"  itself is nebulous and controversial.

Level matching things that generally have a flat frequency response, such as most good amplifiers, receivers, wires, and CD players is thankfully a much more straight forward process. Thank goodness! I describe the method I used at about 3m42s into this video:

https://www.youtube.com/watch?v=T_V5dPB4dYk

Another thing which is important, yet I hardly ever see anyone talk about it but me, is that not only do you need to carefully level match, you also have to channel balance match. It is not uncommon for amplifiers to have a slight channel misbalance where one channel is for example .2 dB louder than the other, at least at certain settings of their analog potentiometer volume knob. Check for that. In some instances it may be audible in lightning fast switching, like we have in a good ABX test.

How to level-match electronics

Reply #2
Another thing which is important, yet I hardly ever see anyone talk about it but me, is that not only do you need to carefully level match, you also have to channel balance match. It is not uncommon for amplifiers to have a slight channel misbalance where one channel is for example .2 dB louder than the other, at least at certain settings of their analog potentiometer volume knob. Check for that.


I am just waiting for a review where the reviewer admits that he/she preferred the left cannel of system A but the right channel of system B...

How to level-match electronics

Reply #3
^ I notice an ever so slight lateral shifting of the central sound stage across the horizon when there is a small channel balance error. This is, after all, one of the reasons why amplifiers have balance controls.

How to level-match electronics

Reply #4
I attempted to give a brief tutorial on how I did it when I conducted a blind test of my "expert listener" audiophile friend and actually started a thread on it at the AVS forum. Within moments of posting it a carnivore from the high-end industry swooped down to intentionally attack and sidetrack the discussion because having the lay public learn what counts and what doesn't in audio, by testing it out themselves, is completely at odds with their marketing strategy of "Trust us, we are more experienced than you and have had training to hear things you wouldn't necessarily notice until you buy an expensive, top-notch system."

New topic. Things become a bit more complex and controversial if you are attempting to level match things that fundamentally have markedly different frequency responses, such as speakers and headphones. Say for example one speaker has a stronger level of bass than the other one being tested. Do you level match them using pink noise? Do you level match them at 1 kHz? Do you instead level match them at 500Hz? Do you use a narrow band of noise centered where the ear is most sensitive, around 3.5 to 4 kHz? Do you use A-weighting when you conduct any of these level matches? You will get very different results depending one which exact method you use when the products have certain frequency response deviations between them.

I'm of the mind that one should accept that level matching things like speakers and headphones is so tricky, problematic, and questionable, that "fair, level matched comparisons" simply can't be done. This doesn't stop researchers at Harmon, etc. from publishing papers where they say "and we level matched" and nobody but me seems to blink an eye. "Our trained listeners preferred speaker A over B due to tonal balance. We level matched the two so that couldn't have influenced their selection" Um. now wait a minute. If you level matched them using A-weighting and speaker A has a broad peak at 4kHz that speaker B doesn't, I'd hardly describe the two as being "level matched" using that method because the very concept of what is "correct in all situations"  itself is nebulous and controversial.

Level matching things that generally have a flat frequency response, such as most good amplifiers, receivers, wires, and CD players is thankfully a much more straight forward process. Thank goodness! I describe the method I used at about 3m42s into this video:

https://www.youtube.com/watch?v=T_V5dPB4dYk

Another thing which is important, yet I hardly ever see anyone talk about it but me, is that not only do you need to carefully level match, you also have to channel balance match. It is not uncommon for amplifiers to have a slight channel misbalance where one channel is for example .2 dB louder than the other, at least at certain settings of their analog potentiometer volume knob. Check for that. In some instances it may be audible in lightning fast switching, like we have in a good ABX test.


Wow, how embarrassing for the audiophile.    Thanks for showing me that video, I found it very interesting.

Now I just wish someone could show how level-matching is done, via video to a layman. If I asked you nicely, would you be able to put together a short video showing how its done properly?

How to level-match electronics

Reply #5
I moved recently and it takes me months to fully unpack and sort things. Sorry, no video, but maybe a brief verbal tutorial?

What are the two UUTs or DUTs [units under test or devices under test] you wish to level match?
What device will you use for your A/B switching?
Are you testing yourself or another party?
Do you want maximum sensitivity to pick up on tiny little differences or do you have to adhere to some idiot audiophile's mythology based belief system, e.g. "switch boxes cause error so I need the cables actually swapped, instead."
Do you have a CD with test tones [probably pink noise and a 1kHz sine wave]  or do you need a link to a place to download such signals?
Do you want to match levels in the acoustical domain using an expensive, high quality SPL meter or in the electrical domain using an AC voltmeter?
What device(s) will allow you to vary the level of one or both of the DUTs? is it an analog or digital control and what incremental units does it show?

Leaving my PC for some hours. Bye for now.

P.S. Do you want to do a double blind test [needs at least one extra assistant for a hardware test] or single blind? Do you understand the distinction between those or need clarification?

How to level-match electronics

Reply #6
Quote
What are the two UUTs or DUTs [units under test or devices under test] you wish to level match?


Amplifier (AVR) and a power amp.

Quote
What device will you use for your A/B switching?


I don't know. I don't have a switch box, if that is what you are asking. I guess someone will have to manually switch between amps. Or is there another more correct way to go about this that a layman can do?

Quote
Are you testing yourself or another party?


Me, but I would like to test this with other people too.

Quote
Do you want maximum sensitivity to pick up on tiny little differences or do you have to adhere to some idiot audiophile's mythology based belief system, e.g. "switch boxes cause error so I need the cables actually swapped, instead."


I just want to know if I can hear the difference. I want to know if its all in my head. I spent a lot of money on my gear, and I want to find out if my money was well spent or poorly spent, and I can't think of any other way but doing things blind. But I have no knowledge or experience setting up blind listening tests so I don't know where to start.

Quote
Do you have a CD with test tones [probably pink noise and a 1kHz sine wave] or do you need a link to a place to download such signals?


I have a test tone CD.

Quote
Do you want to match levels in the acoustical domain using an expensive, high quality SPL meter or in the electrical domain using an AC voltmeter?


I've been told that acoustical measurements are insufficient for level-matching. I can buy a voltmeter for level-matching, but I'm not a technical guy, hence a video tutorial would be able to help me immensely in understanding how the pros do it.

Quote
What device(s) will allow you to vary the level of one or both of the DUTs? is it an analog or digital control and what incremental units does it show?


I use an AVR which has, I think, 0.5 dB steps.

Quote
Leaving my PC for some hours. Bye for now.


Well, I'm at the deep end here, so by the time you return I might have drowned. 

How to level-match electronics

Reply #7
I agree multimeters are the way to go, but Moran and Meyer used an SPL meter so it can be done acoustically in theory. Radio Shack has a good multimter , analog for ~$25 but I have seen one at Home Depot for even less that might do. Do you have access to either store?

Please list the model numbers of the AVR and amp so I will know if they have things like trim pots, variable gain inputs, analog vs digital controls, room correction circuits, tone defeat/"pure direct" circuits, etc.

OK, now I am really gone for hours...

How to level-match electronics

Reply #8
If your CD player doesn't have dual outs you'll need to split the one set it has with a couple of y-cords. Do you have those?

How to level-match electronics

Reply #9
I agree multimeters are the way to go, but Moran and Meyer used an SPL meter so it can be done acoustically in theory. Radio Shack has a good multimter , analog for ~$25 but I have seen one at Home Depot for even less that might do. Do you have access to either store?

Please list the model numbers of the AVR and amp so I will know if they have things like trim pots, variable gain inputs, analog vs digital controls, room correction circuits, tone defeat/"pure direct" circuits, etc.

OK, now I am really gone for hours...


I own a Check Mate CM-140 SPL meter that has been calibrated at Cross Spectrum Labs, but I do have access to shops relatively close to me that do have volt meters. Not sure how accurate they are, though. I think I've heard from Arnold that SPL meters can't level-match to below 0.5 dB.

Equipment for testing : Marantz SR-6008 AVR. Parasound 5250 S2 power amp. I have other equipment in other rooms, but for now I'll keep it simple.

Quote
If your CD player doesn't have dual outs you'll need to split the one set it has with a couple of y-cords. Do you have those?


What type of outputs do I need? I'm using a cheap Samsung Blu-ray player at the moment. My CDP is being repaired at the moment.

How to level-match electronics

Reply #10
I own a Check Mate CM-140 SPL meter that has been calibrated at Cross Spectrum Labs, but I do have access to shops relatively close to me that do have volt meters. Not sure how accurate they are, though.


No measuring device used for level matching needs to have anything better than nominal calibration. Its about matching, not measuring.

The measuring device has to be highly reliable, and that leaves out acoustic measurements.

Quote
I think I've heard from Arnold that SPL meters can't level-match to below 0.5 dB.



Correct, if that.

Quote
Equipment for testing : Marantz SR-6008 AVR. Parasound 5250 S2 power amp. I have other equipment in other rooms, but for now I'll keep it simple.


Match levels by measuring across the speaker terminals while playing a CD with relevant test tones on it.  Switch back and forth between the two signal paths and set gains until the levels match witni 1% which is about the same as 0.1 dB.

Here is a very credible but inexpensive DVM:

http://www.ebay.com/itm/UNI-T-UT-61E-Moder...r-/161376692778

How to level-match electronics

Reply #11
I misspoke earlier about where the y-cords are placed.

I'm thinking you use your SR6008's preouts to feed the Parasound amp and you don't own an outboard preamp. That's a problem.

Here's how I did it, showing the signal flow, kind of:

1kHz test tone CD>
Disc player [BD is OK]>
preamp [this is your master volume knob so you can set the volume on the fly, even mid test]>
dual pre outs made by splitting the preamp outs RCA L and R into L1 R1, L2 R2>
one half goes to cheapo competitor [your Marantz AVR in your case]
other half goes to high end competitor [Parasound amp]

Speaker Wires are either swapped by hand or you use a speaker level A/B switch box to control which amp is feeding your pair of speakers at any given time. You could build a couple of DPDT switches to accomplish this if you are handy with a soldering gun and/or crimp on disconnects

speakers>
test listener in sweet spot blinded to what is actually playing.

Here's how to use the AC volt meter:

Play the test tone and measure the voltage at the speaker posts. Many people use a resistor as their load but you are using the speaker itself as your load. The analog meter I used had a convenient dB scale right on it but if you didn't have that there are on line calculators to convert volts to dB.

Be sure the two competitors are as close as you can make them, by turning the Marantz's volume knob up or down to match the fixed level of the Parasound.

Unfortunately your Marantz uses .5 dB increments so obtaining an ideal .1 dB match will be iffy, but hopefully you can get close.

Be warned that the Audyssey room correction doesn't actually truly turn off on the digital inputs but if you turn it off and engage "pure direct" you should be safe using the analog inputs, which is what you are doing anyways.

I take no responsibility if every thing blows up, but it worked for me and I won my bet.

How to level-match electronics

Reply #12
Interesting thread.

Quote
Be warned that the Audyssey room correction doesn't actually truly turn off on the digital inputs but if you turn it off and engage "pure direct" you should be safe using the analog inputs, which is what you are doing anyways.


So even if you turn Audyssey off in the receiver setting you are saying that it's still active on the digital inputs? How do you know if its still active?

How to level-match electronics

Reply #13
So even if you turn Audyssey off in the receiver setting you are saying that it's still active on the digital inputs? How do you know if its still active?

My careful auditory analysis, using a lightning fast A/B switch box and headphones connected via a headphone amp driven by the unit's rear preamp outs, showed that my Marantz Audyssey XT based prepro wasn't "transparent" as it should be. I later discovered that although turning "Audyssey XT" to off and even engaging "Pure Direct" did properly extinguish all forms of room correction and speaker misalignment for analog inputs, it didn't disengage the speaker time alignment correction, called "distance", between my front L vs R speakers for any of the digital inputs [HDMI, optical, coax].

Using the front panel headphone jack however properly extinguishes all forms or room correction under all scenarios.

The important take away message is that people, including at least one Stereophile magazine reviewer who divulged he was oblivious to this issue in an AVSforum thread where I mentioned it, who attempt to hear "the native sound of the stereo preamp/amp itself" are quite possibly, accidentally skewing the sound thinking that they are listening to unadulterated stereo sound, but in truth are hearing a phase altered version of it.

My findings were later confirmed by testing carried out by forum member krabapple on his higher end Audyssey XT32 based unit, showing this problem isn't peculiar to just my unit. One can test for it by manually dialing in a gross, easily heard distance error, say 10 ft difference between their FL and FR speakers, and then seeing if it is eradicated to the ear when Audyssey is turned "off" and Pure Direct is engaged. EQ is properly extinguished, by the way; the problem is with "distance" [and maybe ch. level trim too, I didn't extensively test for that].

How to level-match electronics

Reply #14
IIRC, Ethan Winer recommends band-limited pink noise for level-matching speakers.
"I hear it when I see it."

How to level-match electronics

Reply #15
Meyer and Moran have publicly provided the test signal they used, available for download, to set the reference 85 dB SPL they used as measured at the listening chair, however they don't (to the best of my knowledge) specifically state if the level matching of A vs B was done in the acoustical domain, as I had assumed initially, or if it was done in the electrical domain, perhaps using a different test tone for the matching process. Setting the overall gain and matching A to B aren't the same thing.

"File 1:  01_ABX_Level_set.mp3  ( 787k )

This MP3 file is the level setting signal mentioned in the paper on the audibility of a CD-quality loop inserted into a high-bit audio stream, by E. Brad Meyer and David Moran, published in the September, 2007 issue of the Journal of the Audio Engineering Society. The reference system gain mentioned in the paper can be duplicated by playing this signal, a one-octave band of pink noise centered on 1 kHz, so that the level at your listening chair is 85 dB SPL "

BAS article

How to level-match electronics

Reply #16
The problem with the 1 kHz tone is not the frequency response of the speaker, but the frequency response at the listening position. Levels can easily change a dB depending on the position of the mic, position of the speakers, the speaker's radiation pattern, the room ...
"I hear it when I see it."

 

How to level-match electronics

Reply #17
Sorry for not responding sooner, but most of this discussion is going over my head. Is a 1 kHz tone good enough to level-match electronics or is there another method that is more better or more reliable?

I would like to compare the receiver output to my power amplifier output and see if the power amp is making any sort of audible difference to the sound. Unfortunately I don't have an AB switch, and I don't want to put my system in a position that might fry the components.

If my Marantz receiver only has 0.5 dB steps, then that means I can only level-match to within 0.5 dB. Is that okay? Or should I try and match to below that? How would I go about that. Please keep in mind, I'm not a technical guy, just someone that would like to determine if any of my purchasing decisions have any merit.

Are there any places that can build or make AB switch boxes? Or ABX boxes? That would come in handy! It would be great if I could switch between components with a switch of a button.

How to level-match electronics

Reply #18
Sorry for not responding sooner, but most of this discussion is going over my head. Is a 1 kHz tone good enough to level-match electronics or is there another method that is more better or more reliable?

I would like to compare the receiver output to my power amplifier output and see if the power amp is making any sort of audible difference to the sound. Unfortunately I don't have an AB switch, and I don't want to put my system in a position that might fry the components.

If my Marantz receiver only has 0.5 dB steps, then that means I can only level-match to within 0.5 dB. Is that okay? Or should I try and match to below that? How would I go about that. Please keep in mind, I'm not a technical guy, just someone that would like to determine if any of my purchasing decisions have any merit.

Are there any places that can build or make AB switch boxes? Or ABX boxes? That would come in handy! It would be great if I could switch between components with a switch of a button.


When comparing units which have a fairly flat response, such as almost all amps, receivers, and CD players, a 1kHz tone measured electrically with an AC voltmeter to within .1 dB difference or less should be fine. Unfortunately you may not be able to get that close due to the course steps of your volume knob, but the experiment may still be rewarding from a personal perspective, even though you will never be dead certain of the results.

The A/B switcher I used was the preamp's input selector, which then fed two outboard competing units.

 
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