DAC Noise Modulation: Chord DAVE vs Topping DX7 Pro+

[Blumlein 88]

Well I have to admit. It takes very little stress to wipe out my ability to hear noise modulation or dithering differences at -300 db. I'm not sure I can hear -120 db under "stressful" conditions of blind testing.

 

[Sean_S]

I am interpreting Rob’s statement to be implying that MODULATION of the noise floor is what sounds bad, not having a higher noise floor per se. I don’t think you’ve directly rebuffed that by showing the Topping has a lower noise floor, when it has slightly more modulation. I’m sure Rob would say that that difference in modulation is more audible than the absolute difference in noise floor…in fact, I think that’s exactly what he’s trying to say. But I do think you’ve shown that the difference in noise modulation between the DAVE and the Topping makes their price difference appear ridiculous.

 

[JimWeir]

In one of the Chord TT2 review thread, I was asked to comment on noise modulation claims by the product designer Rob Watts. I attempted to recreate his measurements and compare them to Topping DX7 Pro+ which I just reviewed.
View attachment 229006

DAC Noise Modulation
Noise modulation refers to noise floor of the DAC changing with signal. To the extent the signal changes, if the noise floor changes with it, it is said to be "modulated." An ideal DAC would keep its noise floor constant as one has (ideally) nothing to do with the other. In reality activities of the DAC can manifest itself as extra noise, raising that component of the signal.

Chord DAC Claimed Lack of Noise Modulation
Rob Watts claims his DAVE DAC to be completely free of noise modulation and being the only DAC to be so. He backs it with the following measurement:

View attachment 229007

Notations in red are mine. This is the text below the graph:
View attachment 229008

Before getting into the details, the graph shows two overlaid measurements. One is when the DAC is producing a 2.5 volt signal, and the other, when it is producing nothing. From the graph it appears that the noise floor is the same in both measurements, backing what he says.

I wanted to replicate his measurements so that I could test other DACs to see how well they do. As I note above in red, this is made difficult by lack of documentation in the above measurements. The noise floor that you see is the result of both DAC noise and how much FFT has reduced it (called "FFT Gain"). I can make that noise floor as low as I want as long as I keep increasing the number of FFT points. As a result, the comments Rob makes about how low the noise floor is, i.e. -180 dB, is useless. That is NOT the actual noise floor of the DAC. So that claim is wrong although in the context of this comparison, it can be ignored. That is, both the no signal and 2.5 signal measurement are subject to the same FFT gain.

For some odd reason, the output voltage is picked to be 2.5 volt for a DAC that can go up to 6 volts. I suspect this may have been picked because it shows least distortion. So on that front, the claim of low distortion is also misleading especially since 0 dB is NOT set to 2.5 volt. Instead, it is set to 6 volt. In reality then, distortion is NOT -150 dB but something close to -142 dB. But again, in the context of comparing noise floors, we can ignore this.

Noise Modulation Comparison
I took the above graph and applied it to measurements of Topping DX7 Pro+. I played with the FFT samples and measurement bandwidth until I got something similar to DAVE DAC. Something still bothered me though. The measurements I performed of the DAVE DAC did not produce such a clean output. So I stepped back and ran the test against DAVE DAC which I happen to still have (owner is on long vacation). Here are the results for DAVE:
View attachment 229009

We see very different results. Distortion products are much higher (in relative terms) and so is the noise floor. What is more, there is noise modulation although in reverse. Noise floor actually goes up instead of down with no signal! Strange. To measure how much it is changing, I first compensated for FFT gain of 48 dB and then smoothed the two graphs:
View attachment 229010

Smoothing screws up the 1 kHz tone so ignore that as all we care about is the noise floor differential which is 2.8 dB. It is changing from -114 dB to -111 dB. This is barely above best case threshold of hearing. So in an extreme case of 1 kHz tone NOT being audible, and with suitable amount of amplification, one may be able to hear that modulation.

Now let's run the exact same test but simply moving cables from DAVE DAC to Topping DX7 Pro+:
View attachment 229014

We immediately see confirmation of my reviews of both products: Topping DX7 Pro+ despite costing 20 times less, has much lower noise floor. It seems to have more distortion spikes but that is because the noise floor is so low, allowing them to peak through. In absolute levels, it is still superior to DAVE DAC by 6 dB.

It does show noise floor modulation and this time, as expected noise floor goes up with signal. Smoothing and compensating for FFT gain we get:

View attachment 229016

The average noise modulation is 4.2 dB which is just slightly more than DAVE DAC. However, in this case, the modulation is occurring at -130 dB to -127 dB. With threshold of hearing at -115 dB, no way this is remotely audible no matter what contrived test we create for it. It is a completely non-issue and the reason I don't measure it.

Note: these tests are pushing limits of physics and instrumentation. Distortion measurements at -150 dB and lower is just crazy! It is unknown how accurate the AP is in this regard. Ditto for its own noise floor/modulation. When I first started to test the DAVE dac it had small train of pulses which disappeared after warming up. So some variation is to be expected in such tests.

Conclusions
This investigation of noise modulation shows that not only does the DAVE DAC perform worse than shown, but it also suffers from some noise modulation. While this noise modulation is slightly (0.5 dB) less than Topping DX7 Pro+, it happens at the threshold of hearing which may make it audible in pathological situations. Topping DX7 Pro+'s noise floor and modulation thereof is so far below audible threshold that it simply is not an audible concern in any contrived situation.

Maybe company's claim that it is the best there is was due to understanding of DAC performance years back (Rob Watts' post is from 2015 although renewed in 2021). This is certainly not true today where a $699 Topping DX7 Pro+ easily outperforms the DAVE DAC on both distortion and noise performance.

Company needs to provide comparative measurements to other current DACs before continuing to make such objective performance claims. And certainly not push points that are not the strength of its DAC, i.e. noise performance.

Bottom line, noise modulation is not a performance metric to worry about in well implemented DACs.

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As always, questions, comments, recommendations, etc. are welcome.

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Audiophiles are often confused when they see a term like “noise modulation”.
The test for this is to run an amplitude modulated sine wave and see if the noise level varies with it.

This test is demonstrated whe you explain dithering when making a recording, as shown about 2/3rds through this (one of my favorite) videos

 

[amirm]

I am interpreting Rob’s statement to be implying that MODULATION of the noise floor is what sounds bad, not having a higher noise floor per se. I don’t think you’ve directly rebuffed that by showing the Topping has a lower noise floor, when it has slightly more modulation.

I most certainly did. Did you not read the original article? Here is the key measurement and quote:

The average noise modulation is 4.2 dB which is just slightly more than DAVE DAC. However, in this case, the modulation is occurring at -130 dB to -127 dB. With threshold of hearing at -115 dB, no way this is remotely audible no matter what contrived test we create for it. It is a completely non-issue and the reason I don't measure it.

The fact that DAVE's noise floor is also higher is a side-benefit of this analysis. It was not the core.

 

[Sean_S]

I most certainly did. Did you not read the original article? Here is the key measurement and quote:


The fact that DAVE's noise floor is also higher is a side-benefit of this analysis. It was not the core.

Touché, I read right past that, and retract my initial statement. Your excited distain of Watts’ arrogance had me off balance.

 

[dananski]

I don’t think you’ve directly rebuffed that by showing the Topping has a lower noise floor, when it has slightly more modulation.

The 2.8 vs 4.2 dB difference demonstrated here gives the 'win' to the DAVE for implementing its claimed goal, as it did with its reconstruction filter, but accompanied with a huge shrug: So what? The modulation range is entirely above another, cheaper device's and established theory says it won't be audible in either.

There's a bunch of claims, usually but not always by manufacturers, which rely on some technical uniqueness to stand out. For example this DAC with its many taps and 'zero' noise floor modulation. It's implied that this uniqueness is actually audible.

This is somehow a major selling point despite being an inherently fragile claim. Either the principle could be proven incorrect within human audibility, or implementation could be incorrect in the device.

This article indicates that DAVE's implementation of low noise modulation is fine though there's not much setting it apart. I'd like to see the underlying audiblity claims investigated too, but I think that requires large, controlled, double-blind studies. The reviews here don't claim to look beyond well-established audio science as far as I have seen. And this is generally very wise. Go into the weird unverified frontiers of science and you will find antivaxers, perpetual motion machines and the occasional sensible thing that nonetheless might still have a methodological error to be picked up by someone two years later.

 

[PeteL]

The 2.8 vs 4.2 dB difference demonstrated here gives the 'win' to the DAVE for implementing its claimed goal, as it did with its reconstruction filter, but accompanied with a huge shrug: So what? The modulation range is entirely above another, cheaper device's and established theory says it won't be audible in either.

There's a bunch of claims, usually but not always by manufacturers, which rely on some technical uniqueness to stand out. For example this DAC with its many taps and 'zero' noise floor modulation. It's implied that this uniqueness is actually audible.

This is somehow a major selling point despite being an inherently fragile claim. Either the principle could be proven incorrect within human audibility, or implementation could be incorrect in the device.

This article indicates that DAVE's implementation of low noise modulation is fine though there's not much setting it apart. I'd like to see the underlying audiblity claims investigated too, but I think that requires large, controlled, double-blind studies. The reviews here don't claim to look beyond well-established audio science as far as I have seen. And this is generally very wise. Go into the weird unverified frontiers of science and you will find antivaxers, perpetual motion machines and the occasional sensible thing that nonetheless might still have a methodological error to be picked up by someone two years later.

Sure but ranking DACs in a chart with great, good, fair mention, in some way also « imply » That when you are at the very top, you are getting something audibly better, and since no other factors than audio performance are reviewed, and those device don’t do anything else than delivering something meant to be heard. Not audibly better, means not better period, in term of the measured metrics. Basically there two questions. Does the dacc does it claim it does, is it audible is not, in general what get’s a product praised or dismissal s not about audibility, it’s about «competitiveness, but competitiveness at what? many time they are not even listened too, assuming it’s just fine. It just should be a bit clearer than DAC number 15 in the chart, is equally good in term of what has been assessed here as DAC number one, That there is nothing that has been demonstrated in these measurments that should make you chose one over the other and to assess which is the best of the two DAC comes down to other factors that the reviews don’t give us.

 

[amirm]

Sure but ranking DACs in a chart with great, good, fair mention, in some way also « imply » That when you are at the very top, you are getting something audibly better, and since no other factors than audio performance are reviewed, and those device don’t do anything else than delivering something meant to be heard.

The entire effort here is around engineering excellence. Topping brings it not by chance, but being in top tier of SINAD. You get to that position by having extremely low noise floor which is what it has. Another DAC in the "fair" category would lose DAVE DAC.

 

[PeteL]

The entire effort here is around engineering excellence. Topping brings it not by chance, but being in top tier of SINAD. You get to that position by having extremely low noise floor which is what it has. Another DAC in the "fair" category would lose DAVE DAC.

Ok, I personally disagree that this is the main way to demonstrate engineering excellence, but I get your point. All these top tier DAC using near flagship reference design get the same result plus ou minus 3 inaudible, thus unsignificants dBs.

 

[Lukino]

It's about money. More money, more purity of engineering, etc. Unfortunately, this does not apply in the audio business. Thanks to measurement, untruths and marketing fabrications are revealed.

 

[PeteL]

It's about money. More money, more purity of engineering, etc. Unfortunately, this does not apply in the audio business. Thanks to measurement, untruths and marketing fabrications are revealed.

In my book, great engineering is being great at solving a real problem, and being able to concretize it.

 

[Lukino]

This is how it should be. Real engineers should produce verifiable displacement based on measurements. The point is that many sell DACs for xxxx dollars and pack a 250 dollar DAC in 4kg of aluminum. Hence the accuracy on this forum. Thanks Amir.

 

[PeteL]

This is how it should be. Real engineers should produce verifiable displacement based on measurements. The point is that many sell DACs for xxxx dollars and pack a 250 dollar DAC in 4kg of aluminum. Hence the accuracy on this forum. Thanks Amir.

When you say « Pack a 250 dollar DAC » You mean, pack what 250$ for a DAC can get you in 2022 correct? No worries I am not tryingto say the cost is justified, just trying to assess what you mean, You mean he could have just taken a Topping and hide it in the enclosure? Yeah, today Chord might as well just do that I agree.

 

[Lukino]

When you say « Pack a 250 dollar DAC » You mean, pack what 250$ for a DAC can get you in 2022 correct? No worries I am not tryingto say the cost is justified, just trying to assess what you mean, You mean he could have just taken a Topping and hide it in the enclosure? Yeah, today Chord might as well just do that I agree.

Could but....business. Not engineering. Yes at the $250 DAC level.

 

[PeteL]

Could but....business. Not engineering. Yes at the $250 DAC level.

Personally I may be critical of the price, I may as well be critical of marketing and audibility claims, all that is wrong. Now, The truth it is that Rob Watt, is part of a handful of engineers that have proven to be able to build a dac from scratch that performs to the level of perfectly converting those bits at the limit of any degradation that is possible for a human to register and to do this seven years ago. There is him that did, therés Putzeys with Mola Mola venture, Who else really?I’d be happy to increase that pool of people, there got to be others. There has been some R2R measuring poorly, Schiits tryouts in discrete DACs Also didn’t reach these levels. Really, When you are one of the 2-3-4 person in the world that can pull that off, may it be possible that somehow you get so taken that you think you hear stuff that don’t exist and that you think that you have the authorithy to say it, I don't know, It may get to his head. But again… Who else than him and Putzey’s have proven can make that? Yes the developpers at AKM ESS or others, but it’s different, those are huge Engineering teams, leaded by a head engineer but on really incrementals, decade long IP builds.

 

[Lukino]

Personally I may be critical of the price, I may as well be critical of marketing and audibility claims, all that is wrong. Now, The truth it is that Rob Watt, is part of a handful of engineers that have proven to be able to build a dac from scratch that performs to the level of perfectly converting those bits at the limit of any degradation that is possible for a human to register and to do this seven years ago. There is him that did, therés Putzeys with Mola Mola venture, Who else really?I’d be happy to increase that pool of people, there got to be others. There has been some R2R measuring poorly, Schiits tryouts in discrete DACs Also didn’t reach these levels. Really, When you are one of the 2-3-4 person in the world that can pull that off, may it be possible that somehow you get so taken that you think you hear stuff that don’t exist and that you think that you have the authorithy to say it, I don't know, It may get to his head. But again… Who else than him and Putzey’s have proven can make that? Yes the developpers at AKM ESS or others, but it’s different, those are huge Engineering teams, leaded by a head engineer but on really incrementals, decade long IP construction.

Yes, some work was done by RW, etc.... It has to be left.... And then they started abusing it, but that's to be expected when money is involved. That's the bad thing about it. Further, they only cover up lies and exploit the audience's ignorance. But thanks to the people who stop this audio propaganda. This forum. Speaking of which, I'm looking forward to the new AKM and ESS products...

 

[Phorize]

Amir: The measurements don't support your claims Rob

Rob: Measurements don't tell the whole story Amir, you need to listen

Amir: When you listen, do you perform a double blind test?

Rob: No, that's to stressful Amir

Amir: Thanks for the interview Rob

Audiologist: why are all of you middle-aged/old men arguing about this? It's like worrying about the performance of the boxing gloves you are going to wear when you fight Tyson Fury.

 

[Geert]

I am interpreting Rob’s statement to be implying that MODULATION of the noise floor is what sounds bad, not having a higher noise floor per se.

That's indeed what Watts believes in. A year ago I made an analysis of a presentation he did, discussed in the 300dB topic.

Quoting from my analysis:

At 11:08 Watts states you can hear noise floor modulation below the level of measurability.
At 11:29 he applies that theory to mains cables, so it's not only about filters in DAC's.
At 11:44 he repeats immeasurable small levels of modulated noise can be detected by the brain, which affects sound timbre.
From 13:00 on he explaines how distortion between -130 dB and -150 dB is easily audible. OK, not -300 dB but does -150 dB make more sense?
At 20:46 he states no matter how small an error in a small signal is, it's audible. (Error refers to small signal linearity I think, as he explained before). From here on he applies this small signal theory to the noise floor of noise shapers, and that's where the -350 dB refers to. Not filtering but noise shaping. This time there's an effect on perceived depth
This is summarized at the slide at 23:10, which also states this theory explains why interconnects sound different.
At 28:20 he explains how noise floor modulation is responsible for the sound difference between different DAC concepts, like R2R DAC's.

Still complaints anyone about misquoting Watts?

 

[JSmith]

It may get to his head.

Let's not forget... "blind tests are stressful". That honestly says it all really... he knows.


JSmith

 

[PeteL]

Yes, some work was done by RW, etc.... It has to be left.... And then they started abusing it, but that's to be expected when money is involved. That's the bad thing about it. Further, they only cover up lies and exploit the audience's ignorance. But thanks to the people who stop this audio propaganda. This forum. Speaking of which, I'm looking forward to the new AKM and ESS products...

Of course money. That would be very naive to believe any engineering development is nor about money.