Measurements Of Chord Mojo

[Arnold Krueger]

How do you level match with a single volume control Arny?

Also passive volume controls like that impact the frequency response at different levels. And some introduce channel imbalance.

Depending on the situation, one may need up to 4 of these boxes, but the costs remain reasonable.

Using separate one for each channel makes things easier.

Resistive attenuators do create the the risk of adding distortion, noise, and added contaminating signals.

The most probable loss is frequency response losses Due to capacitive cable loading.

You have to be aware of what you are doing.

You balance the technical risks against the certainty that a potentially audible mismatch completely destroys the comparison by adding a highly audible influence.

 

[Arnold Krueger]

OK, all the files have been amplitude corrected exactly to match the PK amplitude of the original including correcting the minor channel imbalance .

http://alanmarch.hopto.org/sharing/3re1FgOSQ

Link is unreliable but when it works, it gets me to a login that seems to want a password...

 

[March Audio]

Link is unreliable but when it works, it gets me to a login that seems to want a password...

Hi
There have been some changes to my Nas setup, I will up date the link

 

[Arnold Krueger]

Got the 9 files. Thanks!

 

[trl]

I know Chords Mojo is on Amirs ToDo list, but I have decided to publish my measurements as another data point to compare our two measurement systems for consistency.
[...]

Linearity - Extremely good
View attachment 11230

I havent tested with headphone loads, just as it would be used as a line level source with the QA401 high imput impedance. I wouldnt hesitate to use this DAC as a primary source in a full system despite its portable pretensions. It measures very well.

Im always very cautious when offering subjective impressions, but IMO this DAC does sound a little bit different to most. I find most DACs boringly similar despite what some say. I dont think I hear more with this DAC than any other good DAC, but this has a slightly different tonality. It is my "daily driver" used with Oppo PM1 cans. Oh yeah, it goes loud!

Great review, so from my understanding is this the best DAC ever measured here on ASR? Does it gets a 22- bits of resolution (ENOB), right?

 

[Blumlein 88]

Hi Blumlein 88 , I finally performed this ABX test, only tried the once but here is the result:

foo_abx 2.0.4 report
foobar2000 v1.4 beta 11
2018-04-15 20:34:36

File A: 01 - Before You Accuse Me.flac
SHA1: d25ca7e4d5881a3dc1b9aa892f40203b675086b9
File B: 02 - Before you Accuse Me Chord Mojo.flac
SHA1: 564af148a0856ff60cdaf8a664f6eb853350d6b5

Output:
DS : Digital Output (Chord Async USB 44.1kHz-768kHz)
Crossfading: NO

20:34:36 : Test started.
20:41:39 : 01/01
20:47:25 : 02/02
20:48:27 : 02/03
20:49:12 : 03/04
20:50:36 : 03/05
20:51:22 : 03/06
20:52:04 : 04/07
20:52:22 : 05/08
20:52:57 : 06/09
20:53:29 : 07/10
20:54:00 : 08/11
20:54:17 : 09/12
20:54:33 : 10/13
20:54:52 : 10/14
20:55:18 : 10/15
20:55:31 : 10/16
20:55:31 : Test finished.

----------
Total: 10/16
Probability that you were guessing: 22.7%

-- signature --
99c1f417315675f1db24f154ab9225798ce7a36d

So you are 77.3% sure!

 

[Jakob1863]

<snip>
20:54:52 : 10/14
20:55:18 : 10/15
20:55:31 : 10/16
20:55:31 : Test finished.

----------
Total: 10/16
Probability that you were guessing: 22.7%

-- signature --
99c1f417315675f1db24f154ab9225798ce7a36d

Just as a quick remark, it still isn´t such a good idea to do 16 trial ABXs unless listeners detection ability (wrt the EUT) is really good under the test conditions. Otherwise the risk to miss something due to low statistical power is quite high.

 

[dc655321]

Great review, so from my understanding is this the best DAC ever measured here on ASR? Does it gets a 22- bits of resolution (ENOB), right?

I cannot comment if it is the best dac ever measured on ASR, but it certainly measures very well in this instance.
Linearity (measured here) is not quite the same thing as ENOB.
@amirm may comment further, but he uses a criterion of 0.1 dB deviation as the factor to differentiate dacs on their linearity.
As he's stated on another thread (can't remember which one ATM), using such a small value permits differentiation of the really good from the good and not-so-good.

 

[March Audio]

Great review, so from my understanding is this the best DAC ever measured here on ASR? Does it gets a 22- bits of resolution (ENOB), right?

Well there are other things to consider but yes its the best linearity that I have measured. One thing I do need to do is test with headphone and dummy loads.

In comparison the Motu 8a performance is pretty much as good. It has better IMD and due primarily to the higher output voltage better noise performance. https://audiosciencereview.com/forum/index.php?threads/motu-8a-measurements.2342/#post-72963

It should be noted that Amirs measurements are different to mine so it may be unfair to directly compare. @amirm might be able to explain the detail of his measurements for comparison. I know he has used 2 methods, directly from the AP and exported to excel

For info this is what I do. Noise has an impact on the lower level measurements so I try to minimise this effect by using a high resolution FFT, 262k point. This isnt really for frequency resolution but long sample time. I also average 50 readings. Tne input signal (1kHz) is generated in Adobe Audition and played back by Roon.

 

[March Audio]

So you are 77.3% sure!

I think I need to perform more tests with different tracks to draw any firm conclusion

 

[March Audio]

Just as a quick remark, it still isn´t such a good idea to do 16 trial ABXs unless listeners detection ability (wrt the EUT) is really good under the test conditions. Otherwise the risk to miss something due to low statistical power is quite high.

You could say I went off the boil towards the end..........or I wzs guessing well at the beginning

 

[amirm]

Well there are other things to consider but yes its the best linearity that I have measured. It should be noted that Amirs measurements are different to mine so it may be unfair to directly compare.

For info this is what I do. Noise has an impact on the lower level measurements so I try to minimise this effect by using a high resolution FFT, 262k point. This isnt really for frequency resolution but long sample time. I also average 50 readings. Tne input signal is generated in Adobe Audition and played back by Roon. @amirm might be able to explain the detail of his measurements for comparison. I know he has used 2 methods, directly from the AP and exported to excel.

Both of my measurement styles are different. I don't do any frequency analysis. Rather, I bandpass filter the one tone and measure it using an analog meter. Your FFT method is more noise-free so likely to show better results.

 

[trl]

[...] so likely to show better results

Got it now, so BE718 is more generous than Amir.

 

[Thomas savage]

Got it now, so BE718 is more generous than Amir.

No one is more generous than our graceful leader and inspirational King Amir to suggest othwise is heresy and punishable by death.

 

[amirm]

Got it now, so BE718 is more generous than Amir.

Said differently, I am grumpier than he is.

 

[Wombat]

Said differently, I am grumpier than he is.

Only about MQA that I can recall.

 

[Jakob1863]

You could say I went off the boil towards the end..........or I wzs guessing well at the beginning

There is simply a problem regarding statistical power and the according sample size because that depends on the detection abilities of the listener (detection ability under the specific test conditions) and the effect size.
Foobar let you choose your own decision criterion, but doesn´t supply any information about the dependencies.

Let´s say that you choose the traditional/usual 0.05 criterion than you´ll take any result with a probablity of p < 0.05 (means the probabilit to reach a result by pure random guessing) as evidence that you could hear a difference. So the error risk that you would accept a result as evidence although it could have been due to random guessing is 5% (in the long run).

Statistical power describes the strength of your test to detect a difference if there is a detectable difference (more precise to reject the null hypothesis correctly, because it is false).
So if you want to balance both error risks you should aim for a statistical power of 0.95 and now the effect size/detection ability determines the sample size needed to reach those numbers for both error risks.

Let´s say for example that the effect size is 0.2 which means your actual p is 0.7 instead of p = 0.5 as assumed under the null hypothesis, than you´d need a sample size of 67 trials.

If you´d aim for the minimum statistical power that is nowadays commonly used (1-beta) = 0.8 you´d still need 37 trials at least.
If the effect size or your detection ability is only at p = 0.6 you´d need even 158 trials (same conditions, power = 0.8, alpha risk = 0.05). All numbers so far calculated for an one-sided test.

If we calculate the achieved statistical power from the example above (assumed actual p = 0.7, 16 trials, alpha = 0.05) we get the result:
power = (1-beta) = 0.445 , so the probability to get a false negative is 44.5 %

If we calculate the same for an assume actual p = 0.6, we get:
power = (1-beta) = 0.167, so the probability to get a false negative is even higher at ~83%

 

[Jakob1863]

@BE718 ,

the measurement system that you´ve purchased is a nice one, but you could expand it´s abilities when measuring at FS or a couple of dB´s below by using a separate Notchfilter for the fundamental, see for example:

http://www.tronola.com/moorepage/Twin-T.html

 

[March Audio]

Cool, I will do more trials over a period of time

 

[March Audio]

@BE718 ,

the measurement system that you´ve purchased is a nice one, but you could expand it´s abilities when measuring at FS or a couple of dB´s below by using a separate Notchfilter for the fundamental, see for example:

http://www.tronola.com/moorepage/Twin-T.html

Yes, fully aware of this and discussed elsewhere. its a project already in progress. as mentioned in the op the 20dB attenuator assists with the distortion measurement at the expense of noise floor.