Yet another A/B test of DACs

[pma]

When you really want to find out the differences between DACs level matching is important within 1% (0.1dB).

And this I am doing in CoolEdit Pro, and not by a Bastlerei method . However, no ABX difference between two at least average DACs.

 

[solderdude]

For those not knowing what Bastlerei is... a Bastler is German for DIYer as in MacGyver way (working with what one has at hand).

 

[pma]

BTW, many guys now have BTL class D amps with both of binding posts live, floating around 1/2 PSU voltage at idle and none of them grounded. Will you suggest a null method then? Which of outputs, OUT1+, OUT2+ x OUT1-, OUT2-??

 

[solderdude]

Will you suggest a null method then

I won't. As said... it was just an alternative method mentioned by John.
I also wouldn't recommend just any multimeter and inputs from soundcards can also be overloaded nor would matching by ear or SPL meter work properly.

You will have to know what you are doing, how and why and what to expect under which circumstances ... in all cases.

 

[Blumlein 88]

I think I have figured out a way to adjust by ear to within .1 db. I'll be famous for sure.

Most of you are familiar with beat frequencies. We use it when tuning instruments. If two frequencies are very close to each other we hear not just the tones, but a difference tone.

So I put 440 hz in the left channel, and 445 hz in the right. Clearly you hear a beating at a 5 hz rate. The intensity of the beating is greatest with both signals equal. Increasing or decreasing one of the signals reduces the intensity you hear of the 5 hz beating. It is very obvious when the difference is only .1 db between the signals.

So I created a 15 second signal and the middle 5 seconds one channel is .1 db low. The transition is obvious. It is fiddly. But you adjust until the beginning and end are clearly louder than the middle 5 seconds. And then you adjust for maximum intensity. If you go too far the middle sounds loudest and you back up a bit. You do have to keep your head completely still during this. Moving your head will obscure the effect. I could hear it even with a .05 db difference. I could not hear a .03 db channel imbalance. BTW this was over speakers. Haven't tried headphones I'd think it works even better over phones.

Try this out, and tell me if I've missed some glitch that prevents it from working.

Maybe @j_j can explain pitfalls of doing this over headphones.

 

[RayDunzl]

Haven't tried headphones I'd think it works even better over phones.

Speakers will produce the beating in the air.

Headphones would be interesting, with the different signal in each earpiece, since there is no beating, except that which your brain creates.

You might try that condition right away.

I was surprised (somewhat) to hear beating where none physically existed, one pure tone in each ear.

I think @j_j explained it all to me, but I can't find the posts right now.

 

[Blumlein 88]

I've tried it with headphones. It does work, but is a bit less obvious. Other caveats. You have to get seating pressure of the phone on your ear even or that changes the relative loudness enough to be corrupting. For the same reason you have to keep your head still. And this one is weird, don't move your eyes. Moving your eyes side to side modulates the intensity of the beating. Why do people listen on headphones anyway.

I'll probably start a thread on this later today. It works great over speakers. Maybe we can figure out the optimum base and beat frequencies.

 

[raif71]

Get a cable like this one. Male on both ends. Plug it in place of your headphones. Many people have one to connect telephone to car stereos.
You can use the other end to check voltage output with a multimeter. It can be a bit fiddly, but not terribly so. Put the black lead on the sleeve or ground portion. Put the red lead on one of the other parts of the plug to check either right or left channel. If you have balanced headphone outs, then this will be different.

Find a comfortable volume for your test with one of your DACs. Without changing volume send it a test tone, 1 khz is fine, 440 hz might be better for a cheap multimeter. I'd suggest a -6 db tone. Write down the voltage. Switch to your other DAC, and sending it the same test tone, adjust volume on it to match the voltage reading with your first DAC. Get the two within 1% of each other. If you read 1.oo volts then you want something between .99 and 1.01 volts. Takes longer to read these instructions than to do it once you have done it a couple times.

Now as long as you don't change volume on either DAC you can switch back and forth with matched volumes. If you have a headphone amp you can even change volume on it as long as the DACs are putting out the same voltage/volume.

View attachment 108402

Ok, for balanced measurement, suppose I connect the amp as such:

So, measurement of the the voltage using DMM, would be black lead to "G" and the red lead to ?. Thank you in advanced.

 

[JustAnandaDourEyedDude]

Ok, for balanced measurement, suppose I connect the amp as such:
View attachment 108531

So, measurement of the the voltage using DMM, would be black lead to "G" and the red lead to ?. Thank you in advanced.

With the Pentaconn connector, to measure the left channel the black lead of the MM connects to L- and the red lead to L+. Similarly, for the right channel, black lead to R- and red lead to R+.

 

[Blumlein 88]

With the Pentaconn connector, to measure the left channel the black lead of the MM connects to L- and the red lead to L+. Similarly, for the right channel, black lead to R- and red lead to R+.

Yes this. You are measuring the difference between plus and minus. You don't use ground for these purposes.

 

[DSJR]

Sorry to chip in, but A-B comparisons MUST be as precisely level matched as you can get it. I tried to do an A-B of two radically different signal paths and one was ever so slightly lower in level than the other and lost out. Once I matched them I couldn't tell the difference and once I got confused as to which was which, the previous quieter one if boosted a tad too much then 'sounded' better. Total crap comparison in your collective eyes, but it taught me several lessons I've not forgotten as really, the radically simpler signal path should have been 'vastly' better - but it wasn't...

Anyway, good luck with the testing as it should be plain sailing once the initial tweaks have been ironed out

 

[Tim Link]

Speakers will produce the beating in the air.

Headphones would be interesting, with the different signal in each earpiece, since there is no beating, except that which your brain creates.

You might try that condition right away.

I was surprised (somewhat) to hear beating where none physically existed, one pure tone in each ear.

I think @j_j explained it all to me, but I can't find the posts right now.

I was also a bit surprised to perceive beating on headphones with pure tones in each ear.

 

[Blumlein 88]

Okay so this has turned into a cautionary tale. I thought I could hear the beat frequency change volume when on channel was reduced in level by only .1 db which was surprising. Of course I was looking at the sound editor and knew where I had made the changes. Don't under-estimate your eyes ability to confound your ears.

I found when I covered the screen and listened the difference disappeared. Once gain sighted listening strikes. I can hear a difference, but only when on channel is reduced about 1 db which is not surprising.

Mea Culpa!

 

[andreasmaaan]

Okay so this has turned into a cautionary tale. I thought I could hear the beat frequency change volume when on channel was reduced in level by only .1 db which was surprising. Of course I was looking at the sound editor and knew where I had made the changes. Don't under-estimate your eyes ability to confound your ears.

I found when I covered the screen and listened the difference disappeared. Once gain sighted listening strikes. I can hear a difference, but only when on channel is reduced about 1 db which is not surprising.

Mea Culpa!

Ha! Still, very interesting idea.

(My word of caution was going to be about the inbuilt assumption that any difference in hearing acuity between the L and R ear is so much less than 0.1dB at the frequencies of the beat tones that it is not a significant factor, which I doubt is generally the case.)

 

[Nango]

@raif71 Don't forget to tell us the music you use and where you think you hear any differences.

 

[raif71]

With the Pentaconn connector, to measure the left channel the black lead of the MM connects to L- and the red lead to L+. Similarly, for the right channel, black lead to R- and red lead to R+.

I suppose in this case, it is ok just to pick either L or R, for the measurement ie be consistent for each setup, right?

 

[JustAnandaDourEyedDude]

I suppose in this case, it is ok just to pick either L or R, for the measurement ie be consistent for each setup, right?

Yes, pick either and be consistent between the DACs, i.e. pick just the L for both DACs or just the R for both DACs to match the voltages to within +/- 1%. Please see Post #26 and Post #58. Same thing even if you use unbalanced (single-ended) 3.5mm connectors: pick a single channel, either L or R, consistently for both DACs, to match the voltage.

You can separately verify that (in the case of a stereo sine tone played from a file), the voltage of L and R channels of a DAC are the same to within +/-1%. As pointed out in Post #58, Amir has measured channel imbalance in some DACs, which may be sufficient to cause a real and repeatable sensation of difference between the two DACs you test in the listening part of the test. Or you can do one-eared listening tests, with a earplug in the other ear.

 

[bennetng]

CoolEdit Pro

Perhaps you (and other Adobe Audition users) can try oldsCool mentioned in this post:
https://www.audiosciencereview.com/...he-obsession-with-dr-meters.11297/post-649576

 

[raif71]

My sanity setup before DMM arrives. DACs are Topping D10s and E30. Amp is Ifi Zen Can. ABing between the 2 DACs, I could not detect any difference.

 

[raif71]

Get a cable like this one. Male on both ends. Plug it in place of your headphones. Many people have one to connect telephone to car stereos.
You can use the other end to check voltage output with a multimeter. It can be a bit fiddly, but not terribly so. Put the black lead on the sleeve or ground portion. Put the red lead on one of the other parts of the plug to check either right or left channel. If you have balanced headphone outs, then this will be different.

Find a comfortable volume for your test with one of your DACs. Without changing volume send it a test tone, 1 khz is fine, 440 hz might be better for a cheap multimeter. I'd suggest a -6 db tone. Write down the voltage. Switch to your other DAC, and sending it the same test tone, adjust volume on it to match the voltage reading with your first DAC. Get the two within 1% of each other. If you read 1.oo volts then you want something between .99 and 1.01 volts. Takes longer to read these instructions than to do it once you have done it a couple times.

Now as long as you don't change volume on either DAC you can switch back and forth with matched volumes. If you have a headphone amp you can even change volume on it as long as the DACs are putting out the same voltage/volume.

View attachment 108402

My DMM has already arrived. Is it ok if I use this cable to attach to DAC and do AC voltage measurements ?

I will match both AC voltages coming out of the two DACs with 1khz tone. After voltage match, I will then attach the two dacs to AB switch and then to the amp. I'm asking this as I don't want to unnecessarily damage my DAC while putting the DMM leads at the 3.5mm jack during measurements. Thanks