[Jawed]

And I guess to say it another way, there are some measurements where JA's AP may have been a limitation with his Dave measurements and very clearly some measurements where his AP wasn't a limitation for measuring Dave and Mojo (and bettered by Holo May and Weiss DAC).

Search is so useful:

Rob's comments on the AP used in Stereophile's DAVE review

The APx555 is a much better instrument than the SYS2722. Chord have one, and when they measure Dave they get -118dB DR - as opposed to -128 dB with Dave into the APX555. The SYS2722 is simply inadequate to measure Dave - indeed John Atkinson confirmed to me in January that they have now acquired an APx555, so I hope to see updated measurements. But even the APx555 has a tough time with Dave, and I am unsure how much THD is actually down to the APx555, as Dave's level is at the innate level of the 555... It's one reason for the Davina ADC project, so that I can get better measurements.

The analog noise with Dave is at -128 dB; I could get better than this, but this would be at the cost of higher THD, which is damaging from a SQ POV. Moreover, the APx 555 can't measure better than -133 dB anyway, and the noise level is so low that it is immaterial subjectively - it's only when noise changes with signal that it becomes important, and as already discussed, the noise change with signal is unmeasurable.

We've been here before...

 

[vkenz]

well maybe, some do gooder can compile all those Q & A?

 

[miketlse]

well maybe, some do gooder can compile all those Q & A?

Many people nowadays seem to use the term ´do gooder' as an insult, instead of ´altruist'. Try visiting the Mojo thread, with the FAQ created by @Mython2 . I havé always described that as an excellent attempt to capture knowledge for enthusiasts, to enable them to enjoy their passion/music.

 

[flyte3333]

Search is so useful:

Rob's comments on the AP used in Stereophile's DAVE review

Rob's comments were before the Weiss and Holo May DAC measurements were performed by the way?

So timeline is important, no?

And it doesn't change the fact that JA's same (low resolution?) AP gear was able to show measurable differences between Dave and Weiss DAC and Holo. Some where Dave measured better and some not, no?

We've been here before...

I can't see how his comments (which were before JA's Holo and Weiss DAC measurements) address this?

 

[Triode User]

Rob's comments were before the Weiss and Holo May DAC measurements were performed by the way?
So timeline is important, no?
And it doesn't change the fact that JA's same (low resolution?) AP gear was able to show measurable differences between Dave and Weiss DAC and Holo. Some where Dave measured better and some not, no?
I can't see how his comments (which were before JA's Holo and Weiss DAC measurements) address this?

Whilst this exchange might be interesting at one level I must say that the big take home lesson for me is that at this level measurements are a poor guide to how a DAC sounds. I have owned a L2 May and can only say that it sounded relatively poor compared to the Dave. I had been considering it for a second system but instead I sold the May and put the Qutest back in that system.

 

[Rob Watts]

When I saw the Stereophile review of Dave I was shocked and horrified to see the results - particularly the 16bit -90.31dB plot. So I requested the exact same unit back, so I could measure it myself - and Chord kindly shipped the unit back to me, and replaced the US distributors' Dave. And I checked the unit out, and it measured perfectly. This is the plot I achieved using my APx 555:

This is visibly a perfect result from this test - you can't even see the differences between left and right. The ringing you see is absolutely correct, being a consequence of an ideally bandwidth limited combination of square waves. No noise is visible at all. Why the review results are so poor I do not know - I did extensive tests and trials to see why the AP SYS2722 gives poor results on this test, but could find no technical reason to explain Stereophile's findings. Frankly, the SYS2722 is an inadequate a piece of test equipment to measure DACs like Dave - even the APx 555 is not fully up to the task.

Just to remind you here are some other plots from Dave using my APx 555:

Like all my DACs this shows zero measurable noise floor modulation; no other DAC at any price point has zero measurable noise floor modulation. This is a very important concept, as it directly ties in with subjective performance - but why can't other reviewers do this test? I have been talking about the vital importance of this for decades, but the audio business continually ignores this vital issue. Why?

No other DAC DAC shows zero jitter on this test. You can just about make out +/- 100Hz sidebands at -165dB - this is from the AP's ADC. The skirting is from the windowing function of the FFT too.

Again the two tone performance is limited by the APx 555 - even so it's substantially lower than any other DAC at any price point.

 

[antastik]

Measurements systems and operators are always going to play a role, especially when the precision level of the instrument itself is approached. This is on the objective side. On the subjective side, Rob, my humble recommendation is to try and provide some form of evidence. Don't get me wrong, I am a fan of your dacs, but I am having trouble justifying to myself how very low noise levels at strange frequencies might affect the audible band. The connection between objective measurements and subjective perception is something that deserves some form of explanation, don't you think?

 

[griff500]

I'm sure my DAVE will sound much better once I have some graphs showing why.

I totally get why measurements can be useful to the people designing DACs but I struggle to understand why some end users get so hung up on it.

Each to their own though.

 

[Kentajalli]

I totally get why measurements can be useful to the people designing DACs but I struggle to understand why some end users get so hung up on it.

Totally agree with the first part of your statement above, measurements are a design tool, what to measure & what not is up to the designer and/or reviewer.
And Mr. Watts is blue in the face as to why reviewers ignore noise floor modulation.
But this place has become a place of learning, thanx mostly to Mr. Watts. It is interesting to know why and how something works, hence .....
Jitter for example was THE most important measurement for DAC's a few years ago. People went into extreme length to get it lowered, few £1000 addon clocks were (are) being sold, yet Chord DACs are jitter free - who was the last reviewer that jumped out of his skin when he saw such graphs???
Yet they argue about -140dB possible noise that is 2dB higher than another DAC! and no talk about noise floor modulation.
It would be fun (educational?), for @Rob Watts to simulate recordings with stepped noise floor modulations, so we could listen for ourselves and hear the effect.
Perhaps one with large modulations, another with moderate and one without.
And yes, no measurement can tell you something will sound good - they can only tell you what will sound bad and is broken.
After all early solid state amplifiers of the 60/70's all measured beautifully against their valve counterparts, but these days we know better.

 

[Jawed]

It would be fun (educational?), for @Rob Watts to simulate recordings with stepped noise floor modulations, so we could listen for ourselves and hear the effect.
Perhaps one with large modulations, another with moderate and one without.

This is a nice idea.

I remember when I compared Hugo TT and DAVE, side-by-side, I was surprised at how clear the noise modulation sounded in Hugo TT. It took me a while to tune in to the specific effects of directly audible noise modulation, but once heard it was unignorable.

This is a great example of how something that wasn't measurable in Hugo TT is clearly audible. Sure the listener needs to be "trained", but it then becomes a lifelong skill.

Apart from literally hearing noise that changes with the music, I discovered that it is also heard as subtly-broken rhythms and timing in general that becomes mechanical. Finally, most problematically, it changes the dynamics of the music, where individual notes become emphasised seemingly at random. Higgledy-piggledy music.

The overall effect is lots of small details and performance cues (emotionality: emphasis, timing etc.) being subtly broken. Because there's so much broken stuff happening continuously, it's hard to realise that this is abnormal, unless you've heard something better.

I believe this is why DAVE is such a shocking upgrade for many people, because the music feels so different.

 

[Currawong]

I have been talking about the vital importance of this for decades, but the audio business continually ignores this vital issue. Why?

I've been ranting about how manufacturers manipulate the crosstalk (vs. frequency) to tune their amps, yet after most of a decade, I've only seen a single comment about it. Likewise, a friend was measuring amps under actual headphone loads, which nobody else until recently thought to do, and suddenly it's a revelation. Recently too, someone thought to measure the phase of amps, which nobody else is doing, or has ever done to my knowledge. Selling judgemental opinions gets more tractions than trying to find any kind of truth.

 

[thePhones]

With every little snippet Rob gives us about the new m scaler I can hear the hype train moving a bit faster. The more he tells the more we want to know...
We have to find strategies to make him say something

Ah I got something…
@Rob Watts: I am pretty sure that the current M Scaler is pretty far behind the competition like MQA… R2R…the list is long.
I guess you don’t even know how many taps the new M scaler might have to finally catch up and get some traction in the market

 

[Jawed]

@Rob Watts is there mileage in using a hypothetical new WTA3 from 256FS to 2048FS? Or, changing WTA2 so that it outputs 2048FS?

The original introduction of WTA2 in DAVE was a big deal and you've talked over the years about the possibility that WTA2 could benefit from more taps. I'm just curious if you've had the opportunity to play with a larger scope than simply increasing the taps in WTA2.

It seems that everywhere you go looking for possible sound quality factors you get big surprises. Apart from pure tap-count (whether in WTA1 or WTA 2) is there a danger that you're running out of surprises left to unearth?

 

[DaveRedRef-III]

When I saw the Stereophile review of Dave I was shocked and horrified to see the results - particularly the 16bit -90.31dB plot. So I requested the exact same unit back, so I could measure it myself - and Chord kindly shipped the unit back to me, and replaced the US distributors' Dave. And I checked the unit out, and it measured perfectly. This is the plot I achieved using my APx 555:



This is visibly a perfect result from this test - you can't even see the differences between left and right. The ringing you see is absolutely correct, being a consequence of an ideally bandwidth limited combination of square waves. No noise is visible at all. Why the review results are so poor I do not know - I did extensive tests and trials to see why the AP SYS2722 gives poor results on this test, but could find no technical reason to explain Stereophile's findings. Frankly, the SYS2722 is an inadequate a piece of test equipment to measure DACs like Dave - even the APx 555 is not fully up to the task.

Just to remind you here are some other plots from Dave using my APx 555:



Like all my DACs this shows zero measurable noise floor modulation; no other DAC at any price point has zero measurable noise floor modulation. This is a very important concept, as it directly ties in with subjective performance - but why can't other reviewers do this test? I have been talking about the vital importance of this for decades, but the audio business continually ignores this vital issue. Why?



No other DAC DAC shows zero jitter on this test. You can just about make out +/- 100Hz sidebands at -165dB - this is from the AP's ADC. The skirting is from the windowing function of the FFT too.



Again the two tone performance is limited by the APx 555 - even so it's substantially lower than any other DAC at any price point.

Thanks for posting those exemplary readings Rob. I wonder do you have readings for when the Pre-amp is engaged? I just wonder what effect (or not) the Pre has on the measurements Edit: Regarding noise floor

 

[DaveRedRef-III]

I don't have any specific recommendations for an ADC - but if you do go down the path of getting an ADC, go for as high a sample rate as possible, preferably 768kHz.

I will be testing my pulse array ADC soon, and if that goes well - please note big if - then a unit will be available to support analogue inputs, as this is my long term intent, as well as producing ADCs for recordings.



Absolutely from a convenience POV; but don't write it off from a sound quality POV either. Analogue has lots of unsolvable problems - for example volume controls. My digital volume control is much more transparent than an analogue one. Moreover, my pulse array ADC is very simple on the analogue side, and of course the DACs are too; we may be faced with greater overall simplicity by using a pulse array ADC/DAC combo than using pre-amps and power amps. My goal is to do exactly that - making digital more transparent and musical than analogue.



The issue is leakage currents from the PSU - and it does vary from country to country - it's never been an issue with me at home, but it can be an issue when I travel. At home my neutral is very close to ground potential, and I think that's something to do with it. Get your electrician to check neutral to ground voltage. Grounding will solve the issue, but grounding via Dave will not be the best from a SQ POV, as the galvanic isolation on the OP's will be shorted out. If you need to ground it using the M scaler BNC input then try to use another ground that is far away from Dave. You could power it via a battery, and that would eliminate the issue too, and give the best SQ.

Another way is to ground via a high resistance value resistor, as the leakage current is only 100uA.



Sure it will be compatible with all dual input Chord DACs for the max upsampling.

Regarding the potential future ADC product Rob, is it you plan to incorporate a couple of 48v phantom powers in the unit for Condenser mics? I obviously understand plans can change but it would be very useful imo.