AQ Jitterbug Measurements

[amirm]

John, I haven't done any testing yet so don't keep questioning me . I have not done this type of testing before so I don't have a lot of answers to give until I see what I am dealing with. It will be a learning exercise and I may hit a dead-end given my capabilities (well above hobbyists but not as someone who works for companies and can afford ultra expensive gear).

 

[jkeny]

Yes, that's true. But jitter can only be directly measured in the digital domain. The J-test is a very reliable indirect measurement of jitter in the analog domain. However, the j-test cannot give you real jitter results.

The J-test was specifically designed to exercise/stress SPDIF receivers with knowledge of their operation i.e it stimulates worse case jitter conditions on an AES3 digital audio connection. What is important here is what causes jitter on USB connections is NOT the same as for AES3 connections - it operates in a different way. So, is a J-test appropriate for testing jitter on USB audio connections?

 

[jkeny]

John, I haven't done any testing yet so don't keep questioning me . I have not done this type of testing before so I don't have a lot of answers to give until I see what I am dealing with. It will be a learning exercise and I may hit a dead-end given my capabilities (well above hobbyists but not as someone who works for companies and can afford ultra expensive gear).

OK, Amir, I understand your position but what my posts are hopefully highlighting is that "useful"/"proper" measurements is not just a matter of using a standard suite of measurements - it requires some thinking about the specific device's operation & what conditions are needed to tease out possible, measureable differences.

The J-test is a good example of this - originally designed to maximally stress the specific operation of AES3 devices - the test was designed as a result of knowing how such devices work & deriving a test signal & measurement as a result

 

[Orb]

BTW, how do people feel about this statement in that review?

"When I first connected the LightSpeed 2G USB Cable and hit "play", Miles stuttered. He skipped. Hmm. I've encountered this before when using other USB cables and the easy fix is to lower the clock setting. Instead I inserted the Jitterbug in between the cable and Mac and no more skipping.
Read more at http://www.audiostream.com/content/audioquest-jitterbug-usb-data-power-noise-filter#dAtpc2CtFGRZGRm2.99"

Well I am a bit leery about adding multiple jitterbugs improving the sound further, where I would only expect it to be noticeable on the primary USB output to DAC, but then I have not listened to it or multiple ones connected so being an armchair critic here
Regarding the Lightspeed cable, would be interesting to see its eye pattern and cable spec measured, could be something there causing it to work better at lower rates if there is an interaction between with Mac - probably one of those unpredictable scenarios like we can see at times with HDMI cables *shrug*.
Not good though from a standards perspective if it was not an user error.
That said the USB standard has quite a bit leeway for the compliance mask/"keep out" zone in terms of its spec-size.
Cheers
Orb

 

[Orb]

..... So, is a J-test appropriate for testing jitter on USB audio connections?

To a certain degree yeah IMO, which is backed up by real world baseline measurements and correlation of performance to subjective review shown by Hi-fi News.
It can also show correlation trends for ethernet audio streaming (which is way beyond its scope-design focus).
Edit:
Just to say the engineers who created Halide Bridge used all the various types of measurements for jitter, including J-test as each has their own benefits and purpose.
Cheers
Orb

 

[Andre Marc]

BTW, how do people feel about this statement in that review?

"When I first connected the LightSpeed 2G USB Cable and hit "play", Miles stuttered. He skipped. Hmm. I've encountered this before when using other USB cables and the easy fix is to lower the clock setting. Instead I inserted the Jitterbug in between the cable and Mac and no more skipping.
Read more at http://www.audiostream.com/content/audioquest-jitterbug-usb-data-power-noise-filter#dAtpc2CtFGRZGRm2.99"

Amir, I could be wrong, but this is a bit out of context. Having read many of Michael's reviews, i believe when talks about skipping and stuttering he is being specific to the Auralic Vega DAC, which has different clock settings.

But to answer your question, i do have reservations about this claim in general.

 

[amirm]

Just to clarify, my read of what he wrote was that once he inserted the AQ in his USB chain, it caused data drops. He "fixed" it by moving where it was inserted.

As Orb mentioned, this says the device is causing data degradation on its own and hence interfering with standard compliance of the rest of the chain. Filtering can change the rise time of USB pulses and cause the receiver to not be able to recover the data. It is therefore a compromise between reliability and reducing the sharp pulses in the receiver.

 

[mauidan]

PS Audio is also working on a USB devise:

http://www.psaudio.com/pauls-posts/bugs-uptones-and-regens/

 

[YashN]

Where do you see that? On the output of the DAC?

No, it was on the USB lines (a DIY short USB cable I was toying with). At least that's what I saw, others may have tested it at the DAC output (Archimago might have). Try for yourself.

 

[Andre Marc]

Just to clarify, my read of what he wrote was that once he inserted the AQ in his USB chain, it caused data drops. He "fixed" it by moving where it was inserted.

As Orb mentioned, this says the device is causing data degradation on its own and hence interfering with standard compliance of the rest of the chain. Filtering can change the rise time of USB pulses and cause the receiver to not be able to recover the data. It is therefore a compromise between reliability and reducing the sharp pulses in the receiver.

Actually, again to clarify, he has had this issue with various USB cables, when he has the Auralic Vega DAC set to the highest clock setting. It clearly causes problems if the host device cannot keep up. So it is an Auralic problem, and quite frankly many high end USB cable are not even up to spec. He has never had this issue with any other DAC. This stuttering problem has been noted in several of his reviews when the Vega was in the system.

 

[YashN]

To my knowledge, the only way to measure what the jitterbug is doing or not doing, would be to have the $40,000 Tektronix analyzer referenced in JA's measurements section. It can measure USB. I know that Gordon Rankin has one and uses it. I don't know whether Swenson has one.

I believe John has a new more powerful scope, so there could be measurements forthcoming.

I don't get the impression things are as easy to measure as most people think.

 

[Joe Whip]

Well, the Jitterbug arrived today and I was able to give it a listen for half an hour. The system had been on for a bit and I plugged it in to the one open USB port on my Macbook Air. The other is feeding the DAC through the Wyrd. My SSD is connected via the Thunderbolt input. Cold right out of the box, colored my impressed. I heard a clear and noticeable improvement. I will give it a longer listen tonight and report tomorrow. The Jitterbug will NOT be going back. I may have to get another.

 

[Andre Marc]

Well, the Jitterbug arrived today and I was able to give it a listen for half an hour. The system had been on for a bit and I plugged it in to the one open USB port on my Macbook Air. The other is feeding the DAC through the Wyrd. My SSD is connected via the Thunderbolt input. Cold right out of the box, colored my impressed. I heard a clear and noticeable improvement. I will give it a longer listen tonight and report tomorrow. The Jitterbug will NOT be going back. I may have to get another.

Thanks Joe;

Mine will be hear today or tomorrow.

But where are your measurements????

 

[Joe Whip]

Right now I am having my afternoon tea watching football (soccer) so no measurements! I can think of better ways to spend $40k!

 

[Andre Marc]

Right now I am having my afternoon tea watching football (soccer) so no measurements! I can think of better ways to spend $40k!

If you don't provide measurements I might have to discount your findings as "hysterical"!!!!

 

[Orb]

Just to clarify, my read of what he wrote was that once he inserted the AQ in his USB chain, it caused data drops. He "fixed" it by moving where it was inserted.

As Orb mentioned, this says the device is causing data degradation on its own and hence interfering with standard compliance of the rest of the chain. Filtering can change the rise time of USB pulses and cause the receiver to not be able to recover the data. It is therefore a compromise between reliability and reducing the sharp pulses in the receiver.

Yeah as Andre says, it is the Lightspeed USB cable that me out of standard in terms of eye pattern/eye mask/"keep out" zone, or with weird cable/connector spec measurements.
The Jitterbug I would say is within specs, the issue probably with the Lightspeed cable to Mac rather than Lightspeed cable to DAC side.
Cheers
Orb

 

[Orb]

I believe John has a new more powerful scope, so there could be measurements forthcoming.

I don't get the impression things are as easy to measure as most people think.

I think you are right on the last point
Pain in the back side I would say, why I think it is easier just to measure in the context of this thread and discussion; so at the DAC analogue output analysing noise and distortion across the audio band (not just 1khz tone) against signal level and also jitter, and we accept it does not necessarily give us the full picture.
Still not simple to do because that is a fair amount of testing data points.

Oh Amir, this is really important I would strongly suggest having a DAC that can use a battery and does not need to be connected to the mains (probably the most sensitive set-up to this), test it with mains and without and if really bored do some quick and dirty tests like that for the MacBook but in reality I assume most listeners will use that always connected to the mains.

Cheers
Orb

 

[Elberoth]

I have the Regen, and the improvement I got with my Trinity DAC is nothing short of stunning. Much greater than any USB cable I have tried and equal to IC or SP cable change.

And BTW - I do not believe you can easily measure cable differencies either; yet, there is a consensus between audiophiles that cables do matter.

 

[Orb]

I have the Regen, and the improvement I got with my Trinity DAC is nothing short of stunning. Much greater than any USB cable I have tried and equal to IC or SP cable change.

And BTW - I do not believe you can easily measure cable differencies either; yet, there is a consensus between audiophiles that cables do matter.

Adam,
what I think should be checked is if the DAC behaviour is the same as what Hi-fi News identified when comparing the Melco N1A to a MacBook; The MacBook was creating enough noise to influence the DAC performance in terms of S/N Ratio and a very little bit with regards to jitter (due to being pretty low in the 1st place with tested DACs) compared to the Melco.
In theory one would expect the Jitterbug to have a similar effect.
Regarding the noise improvement, the listeners are not identifying this as a specific noise trait but it does seem (ideally needs further testing/experience from others) to correlate that they perceive a SQ improvement from the DAC.
But your right measuring cables and getting a good correlation-trend-model is far from easy and still not ideal.
Cheers
Orb

 

[jkeny]

I think you are right on the last point
Pain in the back side I would say, why I think it is easier just to measure in the context of this thread and discussion; so at the DAC analogue output analysing noise and distortion across the audio band (not just 1khz tone) against signal level and also jitter, and we accept it does not necessarily give us the full picture.
Still not simple to do because that is a fair amount of testing data points.

Oh Amir, this is really important I would strongly suggest having a DAC that can use a battery and does not need to be connected to the mains (probably the most sensitive set-up to this), test it with mains and without and if really bored do some quick and dirty tests like that for the MacBook but in reality I assume most listeners will use that always connected to the mains.

Cheers
Orb

Also need to check the grounding arrangements/isolation of the measurement devices too!