DACs and bass response?

Congratulations on fixing your Aqua La Voce! Wonderful that you were finally able to get it to work properly. A pity Aqua couldn’t get their jitter rejection circuits to work as claimed but in truth this seems to be a common problem with many DACs. PLL technology is often inadequate in many DACs and incoming jitter is a horrendous problem.

@audioengr

Why don’t you use an APX555 from Audio Precision?

I cant really tell much from an oscilloscope plot and triggering can be tricky.

@audioengr

All cables will have a spectrum. All will be different, None will be perfect.

That is why you need jitter rejection in the DAC!

@audioengr 

Oh yes I absolutely agree that the J-test is not diagnostic. If there are spuriae then it is unknown where the jitter came from. All it says is that the DAC failed to produce the digital test signal properly - it could be jitter or it coyld intermodulation distortion or both.

However, if a device passes the J-test with perfect results then one can only conclude that all distortion spuriae including any jitter of any sort are all below the noise floor.

Devices that pass this test perfectly are indeed rare which is why I agree that most DACs need a reclocker.

@audioengr 

The J-test does not use probes. I am surprised you are not much more familiar with the J-test, as it is an industry standard jitter test (used by Stereohile and others) and since everything related to jitter appears to be your specialization expertise.

See this link

http://www.nanophon.com/audio/diagnose.pdf

The J-test uses a known digital signal and analyzes the spectrum of the analog final output of the DAC for spurious frequencies that should not be there. It is actually a complete approach to testing the entire audio chain from digital signal passed through any cable into the digital input of the DAC and a detailed examination of the final analog output. Any jitter at all anywhere that reaches the D to A chip will result in quite obvious spurious analog signals that do not match the known input. Any source jitter, cable jitter, interface jitter, LIM jitter and intrinsic jitter (in fact the sum of all and any jitter) is tested for.

@audioengr

I believe your Synchro-Mesh works as you claim from your measurements. I have no hesitation recommending it as I know others with excellent DACs that benefit from source jitter reduction devices including cables.

I also believe many (most) DACs are not at all good at jitter rejection and also have high intrinsic jitter (despite claims to the contrary). So the Synchro-Mesh is a great product for improving sound quality of most DACs.

Since you are clearly able to build a device that takes 800 psec jitter from an Oppo and turn that into 20 psec jitter with your Synchro-Mesh, then why do you believe that nobody else has a DAC that can correct incoming jitter to completely inaudible levels - around 20 psec or less?

As I understand it the J-test was developed by Julian Dunn in the mid 90’s.

It appears to be the best test found so far and is used by AP in their lab test gear. (I dont agree with probes on legs of DAC chips as the probe itself is likely to affect the device itself when measuring timing to such accuracy. I think the J-test known test signal in and a careful look at the perfection of the analog out is much more representative as it tests the DAC as a whole as it is designed to function and including the clock timing accuracy)

A LSB square wave at Fs/192 which produces harmonics right across the audio range. This square wave is coupled with a high level sine wave at Fs/4. The sine wave being a very intense digital full on/off work out (nasty stuff that should produce logic Induced modulation in anything but stellar equipment)

Looks like an extreme DAC jitter work out or jitter stress test to me!

No doubt jitter is still there even on the best devices but to have analog artifacts of jitter sitting below a -150dBfs noise floor seems exceptionally good to me.

https://www.stereophile.com/content/case-jitters

Steve,

What is your opinion on the stereophile J-test?

It measures analog out of a DAC to a test signal - so it checks for both incoming and intrinsc jitter.

What do you think of the typical SOTA DACs that have a noise floor at -150dB when tested for jitter?

How can perfect performance be improved upon and what do you look for when testing an asynchronous DAC of this level and how could Synchro-mesh or another cable improve upon perfect?

@stuartk  

Euphonic would be a tube like sound - richer in even harmonics than is on the recording and can sound wonderful. Your choice as to what you prefer. There is no wrong choice.

@stuartk


You asked about my setup.

Here is a link https://systems.audiogon.com/systems/6257

I think the DAC3 sounds like one of the cleanest and clearest windows to the recording that I have heard so far. Apparently it compares well to PS Audio (see recent Stereophile article). I have heard it against ARC DAC 8 and a Gustard Pro with reclockers/bridge (Singxer SU-1) and it doesnt need or benefit from special cables or reclocking although those other devices did. I would not call it thin. Transparent is the best word. It has an extremely low noise floor so details are highly audible but it remains smooth like vinyl. First device I have heard without the slightest hint of digital glare. I think the latest Weiss, Cranesong Solars and Mytek Brooklyn DAC+ will be similar and equally enjoyable. These latest DACs are astonshingly good and not expensive. Technology Progress is wonderful. If you prefer something euphonic then none of the DACs I have mentioned above should be on your short list.

Per Steve’s recommendation, once you settle on a DAC I recommend you try a bridge/reclocker and different cables/inputs yourself. I found no benefit in the Singxer SU-1 and no difference between various digital inputs but YMMV and certainly many DACs do need a reclocker or a bridge to sound their best.

@stuartk


As far far as I can tell, Weiss, Cranesong and Benchmark use similar methodology to handle jitter.

This article explains how digital processing is done on the Benchmark DAC2. There is a paragraph explaining how timing adjustments are done at always less than 1Hz in the Ultralock 2 approach. Note that adjustments are done in the digital domain which allows very small 4 psec tweaks.

https://benchmarkmedia.com/blogs/application_notes/inside-the-dac2-part-2-digital-processing

I have the DAC3 and it seems to do what they claim and Stereophile gave it a thumbs up recently as they did the Weiss DAC a few years ago.

Bass and power supply are linked in every way. This is because they share the same frequencies. The latest DACs are now using switched mode power supplies to great advantage at ultra high frequencies in order to get power supply noise far far away from the audible range. 

The weak link in any Linear Power Supply (no matter how massive) is that it runs on 60Hz (or 50 Hz) and this is a fundamental bass frequency!!!!!

Wow 800 psec of jitter would easily be audible. Even 20 psec jitter may be audible. This shows the importance of

1) A good modern asynchronous DAC that rejects the always present incoming jitter entirely - so you are left with inherent jitter of the DAC itself (for example Cranesong Solaris claims less than 0.5 psec jitter)
2) If you use a DAC that is not known for good incoming jitter immunity or rejection (perhaps a classic older DAC or something which just sounds good to you) then for goodness sake get Synchro-Mesh reclocker!

Be careful of asynchronous DACs that dont fully explain how they achieve a PLL. The very fact of gently adjusting the timing of a secondary clock to rapid fluctuations in the incoming clock can easily create low frequency jitter!! Some DACs have implemented a control filter on the timing adjustments that limit adjustments to less than 10Hz. Only a DAC that limits master-slave timing adjustments to BELOW the audible range (less than 10 Hz) can guarantee to eliminate all audible incoming jitter.

A poorly designed PLL may reduce jitter but create more audible jitter than a high level of random incoming jitter. The key is to understand that signal correlated jitter is much more audible than random jitter by several orders of magnitude. 20 psec jitter that is highly correlated could be much worse than 200 psec of totally random jitter. So a PLL may actually be a significant source of audible jitter!!! (sounds crazy but it is true)

Jitter affects bass quite a lot. Especially as most DACs have a phase lock loop that creates low frequency jitter. Bass should be neither tight nor muddy but articulate. Tight can be a jitter effect - it can be unwanted overtones. Jitter can easily be misconstrued as detail to the untrained ear.