USB Clock Upgrade My Experiences (so far)

[CoenP]

Hi Nick,

That would be great!

regards, Coen

[acg]

Anthony's Controversial Thought #2

Ok, I have been flat out at work today trying to get finished for Christmas when suddenly I have this eureka moment:  could the noise in the FIFO buffer of the NOS1 work in more than one way?  This is the scenario...data is being written into the buffer and data is being read out of the the buffer at the same time.  If we have 'correction calls' causing the FIFO to do more work than it needs to then in theory the FIFO develops more noise of its own...while it is reading data out to the dac!  In addition to the noise on the ground plane, could this noise from the extra FIFO activity be hitching a ride out of the FIFO buffer with the music file? 

A simple thought, but one that had not struck me earlier, and I apologise if someone else had considered this or if this is ill-considered in the first place.

Cheers,

Anthony

[acg]

Anthony hi,

We are both a little sad to be trawling USB protocol information  . I have posted these points elsewhere but they may help again here.

lets assume for the USB link only that there might be four main forms of error / management interruption to data that could impact sound here (there are properly more, but for now).

1) Processing of resend requests (depends on usb transfer mode used)
2) Bit transmission errors
3) Audio word errors (out of sequence or missing words) 
4) Transfer speed management requests


USB Async transfer mode is intended for media stream transfers of video / data and as you say there is no USB protocol error checking, just signalling from the receiving end to speed up / slow down the link. So here the only point 1 of the points 1 to 4 above would not apply. The rest will apply and there will be no USB protocol handling / correction of errors so once the error has happened it will make it to the DACs as corrupt data and we hear it. Since the data lines are simplex (one set of wires carrying data for both directions) for the receiving end to issue commands to the transmitting end to speed up or slow down it has to interrupt the transfer. This is unlikely to be a "set and forget" tuning by the receiving end because the clocks at both end of the link will drift (I know even the temp stabilised Dexa clocks do this) which means that the speed up slow down requests will happen throughout replay.

Another USB transfer mode is bulk transfer mode. If you read back and look at the hunting for noise thread you will see that this is mentioned. I asked in one of these thread posts IIRC if Peter knows from the source code of the NOS USB driver if bulk transfer mode is used by the NOS interface. This could be very relevant to what we hear. With bulk transfer mode there are CRC checks performed on packets and transfer resend requests are made where there are errors. So in this mode it is possible that all four error types listed above could be happening.

The errors only have to happen at some thing like audio frequency intervals and we are going to hear the effects.

Finally wrt clock quality and the accuracy of transmission over the USB lin. Again as mentioned else where both the transmitting and receiving end of the USB link synthesize their 480mhz transfer clock speed by multiplying the 24mhz oscillator wave form by 20X. This makes phase noise in the 24mhz oscillator VERY important if there is to be a well formed 480Mhz link clock. Consider if one beat of the transmitting 24mhz xtal is say 25% faster this could mean that for 20 beats of the transmitting 480Mhz clock it runs 25% faster than the receiving clock so 20 beats at the transmitting end to a relative 15 beats so 5 beats missed.

This is an extreme (I hope  ) example, but its not hard to see that not having the 480mhz USB carrier running at consistent speed at both ends of the USB link could / will cause all sorts of data transfer problems.

Taking all this into account my view was when I started with DIY clocks and then selected the Dexas was "how would better quality clocks not improve the USB link transfer quality ?" (actually I did have some experience of improving USB clock quality from years ago  which helped. Then it was just a case of waiting for the free PSU offer that NewClassD run on Neutron stars from time to time to come round again)

Its important not to go down the "data is data" route of thinking when tuning the implementation of digital audio components. Practical experience is that if you buy into the data is data approach then there are some really big improvements that can be missed out on.

I think the best thing to do would be to use the information I sent over by email and take to plunge. Build the DIY clocks or put Dexas in. Don't get too hung up on transmission line lengths and noise etc. The effect of improved clocks is much much greater then the electrical effects. Three folks are up and running with Dexas with two more in the pipeline that I know of. Listening to the effects puts a very different perspective on the discussion  .

Kind regards,

Nick.

Thanks for the reply Nick.  I missed the bit in the protocol about the x20 multiplication of the 24MHz clock to 480MHz...interesting...I will have to look that up when/if I get a chance. 

I guess my main beef with the DEXA's at this stage is the hideous cost (nearly AU$2000 for a pair buy the time they get here even with the *free* PSU - that is about one-third of the cost of the NOS1) and the less-than-optimal implementation (the wires).  I don't know anything about their noise characteristics and can't seem to find anything on their website or elsewhere.  If you have some data can you please post it?

So I guess what I am getting at is I think that a comparable result can be achieved with more effort and much less expense by firstly figuring out the exact things that drive the improved sq and then developing a reasonably priced solution.  After all this should be available to everyone and who knows, maybe we will figure out something else along the way that will improve things further.

Personally, I think that yourself and Paul need to get together with Peter and measure some things and listen to some music.  If these clocks are as great as they appear to be and if Peter has not already equalled it with his software 'trimpot' then we really will have a much better idea of where things sit.

I cannot over-emphasize just how much I appreciate all that you are doing and on a lighter note how easily England have rolled over in the cricket (phew - we needed that).

Regards,

Anthony

[PeterSt]

could the noise in the FIFO buffer of the NOS1 work in more than one way?  This is the scenario...data is being written into the buffer and data is being read out of the the buffer at the same time.  If we have 'correction calls' causing the FIFO to do more work than it needs to then in theory the FIFO develops more noise of its own...while it is reading data out to the dac!  In addition to the noise on the ground plane, could this noise from the extra FIFO activity be hitching a ride out of the FIFO buffer with the music file?

Hi Anthony,

Maybe you make it too complicated by putting the emphasis one element (FIFO) too much. I mean, make it more general and anything can happen in your direction.

Side note, but related to some extend : Do we now finally see why any Adnaco (glass) doesn't help and can theoretically only make it worse once the, say, inherent noise is sufficiently under control ?

So, not so new to me. However, we (you) start to come up with other reasons for it to happen.

Let's recall what I have always been saying : XXHighEnd is capable of influencing the DAC, and I know of no other means than that it influences the jitter in there (at the clocking out of the D/A chips).
I have also repeatedly been saying that I can not imagine that this is thermal or other noise inside of the PC doing that, hence that we're influencing the noise that travels over the USB cable. Careful, because the sort of fact that I can not imagine this, doesn't make it truth of course.
But wouldn't it be far more logical by now that the kind of processes we talk about cause this ? And that these processes can be influenced ? Just think of the general term "oscillation" and how the digital data (read : pulses) coming over from the USB cable, hit the pulses in the receiver etc., and that causing the not yet understood nastyness. Actually all is sheerly "created" in-DAC, but the way (and whether) it is created is under our unfluence (now think very generally the number of bytes being in a USB packet (or frame if you like)).

So, *everything* influences to begin with (in-DAC I now mean) and the best influencers will be those with a pattern, preferrably at the ms level or maybe somewhat higher. Well, USB transfer is per 1.25ms, so that's a good start.

Almost offtopic (because I can't do enough with it yet) :
With the software I am as far that I can be too close to limits, across limits and before limits. But I still can't apply enough granularity to really control it. However, it allows me to see things. So, I can repeatedly start playback, wait for a second or two and see the lot go out of sync which I can't explain otherwise than hardware running into eachother (which was my aim, so I'm placebo'd). Sadly I can not really proove this is hardware, because it can also be the cpu itself, where processor cycles just don't match for two processes needing eachother. Hard to explain. But all being OK for a second or two and then collapsing makes me wonder.

Anyway Anthony, when the noise sneaks into the data as you propose, you're suggesting jitter up to the degree of molested samples (but read missed and repeated) which in itself would imply more jitter than ever can be. This can theoretically be in order, but if so I wouldn't expect a better oscillator to sound better (for the D/A I now mean, so not USB). Btw, this can also be seen the other way around : how can a 200fs oscillator sound so much better than a 1ps one while all "scientific tests" indicate that we won't be able to perceive the difference. But alas.
So, I can not imagine that such a thing is the case (high noise in the digital data) *unless* this is again at the 1ms level which makes it happen once in the 1000 or so (768K) samples). Thus, jitter like 1ps is way more low than 1/768000 which allows for the 1/1000 not to be perceived as jitter but something quite else (higher level distortion);

We then could say that once per 1ms or whatever it is, we have high jitter for a very small fraction of time (something like the slew rate of the electronics) that possibly being so bad that a sample is missed or repeated.
And something like this happening once per 1ms gives a nice flair to the sound. Or practice : Once the 1.25ms USB transfer is visible at the outputs, this is perceived as more bass and blanketed highs. Easy to hear and thus easy to measure while this noise is say 135dB down (but rides on the signal).

hmm ...
Peter

[AlainGr]

Peter, sorry to arrive late in the party, but as I understand, you are able to have the Silverstone USB card to work without having the molex connected ?

Alain

[PeterSt]

Alain - No ?
Maybe I wrote something wrongly somewhere, but no. And it seems a virtue to SQ that it does need the Molex (but this is just in comparison which normal MoBo USB and that other card I have which does not need it, plus the report of others with cards that need it ...
(sorry to be complicated)

Peter

[AlainGr]

No problem Peter. I ordered the Silverstone card - the first PCIe standard USB card I have since I got my music pc (the 2 I have are the Sotm USB PCIe card and the PP v2 USB PCIe card... Of course, I do not leave each of them in the pc - just one at a time...

Alain

[Scroobius]

With the Dexa's (USB clocks) firmly established in my system they (or at least the PC Dexa) is less established in terms of its final location. So today I moved the clock and its PS from its temporary location (lying at the side of and outside the PC case) to the inside of the PC case. First I located the clock on a "dummy" PCI card with the PS on the inside back of the PC case. Mmmm something did not sound quite right. So I moved it back outside - OK sounded OK again. So then I tried another location inside the PC this time well out of the way inside. But still the excellent SQ was reduced - slight untidyness in the higher registers but the bass was impacted. This maybe a small change in SQ compared with where my system used to be but it highlighted one of the really big changes the Dexa's made to the SQ and that is in the bass.

Just moving the Dexa's a short distance to the inside of the PC case impacts the bass. It gets a bit "fat" and overblown. OK this maybe a small change overall but now that I am used to hearing excellent bass quality with the Dexa's when it is diminished even slightly you really notice a difference.

OK I will find a way to install the Dexa and its PS in the PC without impacting SQ (parts on the way!!). But this brings me on to the main reason for this post and it is that Less Bass really is much More Bass now in this system - tight controlled accurate sounds on the face of it less than fat and bloated (even slightly). And it also goes right through the mid range impacting the accuracy and tonal quality - at least to these tired old ears it does.

Another always surprising thing is that with each of these improvements is just how much better poor quality recordings sound.

Onwards and upwards to 2014!!

Cheers

Paul

[acg]

Airborne radiation affecting the clocks Paul?

[Scroobius]

Hi Anthony - yes possibly also could be earthing I had to connect the ps and clock earth's to that of the pc. Whereas outside the pc they are floating.

But the strange thing is that the Dexa website states that the mounting screws are earth points, however, I checked them out and they appear not to be connected to anything.

Anyway ps and clock isolated from "earth" inside a project box connected to pe hopefully will sort it.

More tests today.

P

[Scroobius]

Today I found a home inside the pc for the dexa clock and its power supply. They are both tucked well away in the bottom of the hard disc partition of the pc case well shielded from the rest of the pc behind metal partitions and fully isolated from PE.

The surprise (or maybe not that much of a surprise) is that the sound is even better than when they were outside the pc case. A very welcome result. The sound is incredibly smooth but remains dynamic and and attention grabbing when required.

Nick is coming down on Friday so it will be interesting to see what he thinks - things have progressed muchly since his last visit here!!

Mani - you are welcome to join us let me know.

Cheers

Paul

[AlainGr]

Hi Paul,

This seems to confirm that a PC is a bad place to be for a sensitive device and that it would make sense to have some "modular" approach in terms of physical isolation... Not really the way a mobo nor a pc case is really made for...

But it sure is interesting

Alain

[Scroobius]

Hi Alain,

I am listening now to an Album I know really well Wise Up Ghost - Elvis Costello (a stonking good album by the way IMHO). It just sounds superb no hint of harshness a very definite improvement. Elvis's albums have never been at the top of my list for sound quality over produced and hard sounding generally but now I am beginning to wonder. It just does not sound hard anymore.

The dexa modules were isolated from PE outside the case and are also now isolated inside the case. So that just leaves RF. As you say very interesting.

But also interesting is that these (what must be) small changes to the clock on the USB link have such a clearly audible effect on the sound. Whatever the reason USB clocks sure are important to sound quality.

It would be great if in 2014 we can find out why!!

Cheers

Paul

[AlainGr]

Hi Paul,

Well I discover how clocks are everywhere and they interact with each other... I never really read this anywhere else than here, at least for the first time. It is important indeed...

Couldn't we have our "Big Ben" super clock for all USB ports Let's wish for the best !

Yesterday, someone came to change the analog electrical counter for a new, wireless one. I am less convinced about the outcomes of the wireless things, but (it could be expectation bias) I sense there is something in SQ that is better... ????

"Everything Matters"...

Alain

[Nick]

Hi Alain,

I am listening now to an Album I know really well Wise Up Ghost - Elvis Costello (a stonking good album by the way IMHO). It just sounds superb no hint of harshness a very definite improvement. Elvis's albums have never been at the top of my list for sound quality over produced and hard sounding generally but now I am beginning to wonder. It just does not sound hard anymore.

The dexa modules were isolated from PE outside the case and are also now isolated inside the case. So that just leaves RF. As you say very interesting.

But also interesting is that these (what must be) small changes to the clock on the USB link have such a clearly audible effect on the sound. Whatever the reason USB clocks sure are important to sound quality.

It would be great if in 2014 we can find out why!!

Cheers

Paul

Hey Paul,

Position of the clocks certainly has audible effects, my nos is still looking like a project because of this. No top on the box still, maybe some time in 2014 it will finally go back on haha. Right now a long coax for the clock signal and have options regards placement. Seems the best route for SQ.

I found some extruded aluminium boxes for clock and psus at last after a long search so will give these a go within the pc and nos.  The hard drive bay sounds like a nice solution.

I'm looking forwards to a nice session listening on Friday without too much A/Bing to do.... for once  .

Best,

Nick.