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DAC Noise Modulation: Chord DAVE vs Topping DX7 Pro+

Somafunk

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Robbo99999

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My rob watts bullshit bingo card is complete, I win the cuddly toy. (I say this despite owning a mojo2/poly of which I’m perfectly happy with, I wouldn’t choose to buy any other chord products though)
There's just too much snake-oil used to justify the high price of these Chord products, even if Rob Watts might actually believe his snake-oil. Some people seem to lap it up still, but it's just not believable. I suppose it was interesting to see a Rob Watts interview after the various roastings here on ASR, he's not changed his tack, he just must really believe in his creations I guess or he can't leave the situation. Bit of a depressing video, **** it though, he can do what he wants for whatever reasons he wants, just I won't be buying his products, that's fine.
 

johnwmclean

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Dan Clark makes a lots of positive comments about Chord gear and personally uses a TT2 / M scaler and Mojo, comments start around 17.05.
I wonder how Dan created his technical marvels when his choice of electronics is shoddy Chord gear?

Also in context Rob Watts said in that video he spends 300 hours a year flying, I really don’t think it’s much of a stretch to take sizeable portable rig with that amount of time in the air.
 

Music1969

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I wonder how Dan created his technical marvels when his choice of electronics is shoddy Chord gear?

Have you actually read through Hugo TT2's measurements?

Shoddy ?

It is highly transparent... and I don't even own any Chord stuff anymore

If you're argument is cost, well that's irrelevant to the technical stuff it sounded like you were commenting about

 

Robbo99999

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Dan Clark makes a lots of positive comments about Chord gear and personally uses a TT2 / M scaler and Mojo, comments start around 17.05.
I wonder how Dan created his technical marvels when his choice of electronics is shoddy Chord gear?

Also in context Rob Watts said in that video he spends 300 hours a year flying, I really don’t think it’s much of a stretch to take sizeable portable rig with that amount of time in the air.
Cheers for posting that, it was an interesting video to watch anyway re the DCA Expanse headphone! It was interesting when Chord & Rob Watts was mentioned - Dan Clark looked a little uneasy at each mention, initially I thought it was because there might have been a conflict between him not wanting to give any negativity about another manufacturers product juxtaposed with the general ASR perception/influence of Chord & Rob, not to mention that Rob had praised the DCA Stealth as his favourite headphone - however later it turned out at around 35mins (& shortly before) that Dan sounds like he does really notice difference in sound between DACS (and had passed a few blind tests) and acknowledges that he believes there is stuff that the Chord products are doing (re their sharp filters) that are having some positive effects which are immeasurable/"unknown" currently. Dan had said earlier in the interview when Chord products were mentioned the first time that he liked Chord products for their easy ability to drive low impedance headphones, so he discusses Chord twice in that interview. I am surprised by his revelations, and it does add some positive weight to the philosophies surrounding Chord products......I'm not on that same page, but it does go some ways to potentially placing a seed in my brain re the potential benefit of Chord products in terms of their sharp brickwall filter for instance, but the seeds not in there yet, but it's a little closer. They're still overpriced in my mind, and I'm not really further convinced to be honest.
 

Els

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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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How can this and other Chord Dacs measure so bad yet sound so good?
 

Els

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Because your ears are not resolving enough.
Are you an ear doctor? What do you charge? I have 8 Dacs, ranging from 29 Euros to 3000 Euros,<not bragging>. I can hear the diference. The most resolving Dac might not be the best Dac.
 

srkbear

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Are you an ear doctor? What do you charge? I have 8 Dacs, ranging from 29 Euros to 3000 Euros,<not bragging>. I can hear the diference. The most resolving Dac might not be the best Dac.
He was being facetious. Like others who have spent enough time with an open mind on here, he’s aware that DACs don’t “sound” like anything other than the original master. The differences in measurements between DACs tested on here are almost all indistinguishable by the human ear—in other words they all sound the same, if they’re pure DACs. If they’re integrated DAC/amps then there’s an amplifier circuit affecting the end result, but as far as the DAC component alone, they all perform the same task.

Digital audio doesn’t have a “sound”, right? Ones and zeroes. If the DAC is doing its job properly, it should be decoding the digital sample of the original master with the closest fidelity it possibly can. That means with the lowest noise, least distortion, and highest accuracy across the widest dynamic range. Those are really the only factors at play here, and they don’t affect frequency response curves, soundstage, imaging, bass slam or any of that analog stuff. The majority of that is the job of your headphones.

Please stick around and keep listening, there’s a lot of very smart folks on here who can save you a ton of hard-earned cash if you’re willing to keep your mind open. That includes not trusting your ears, they’re tricky…
 
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