[Sasha]

I have posted the questions below in Bryston circle, conveniently mentioning BDP-1 as prime example of well executed PC based transport, but the question can be applied to any well executed PC where power and electrical noise issues were taken care of, with any good sound card such as Lynx AES16 for example.
And since the questions are related to USB/SPDIF converters as well, I thought I would post it here as well, since off-ramp is prime example of such component.
My questions are related to specific application as you can see in the post, so my intention is not to start some kind of senseless argument based on biased views, I would simply like to hear opinions about questions raised, if they make sense to begin with, and I would like all well informed people to contribute.
IMO all these products can co-exist in the market, which one you go with will depend on many other factors, needs and preferences that go far beyond questions raised here.
So here it goes:
Has anyone compared BDP-1 to any of the new USB/SPDIF converters (off-ramp 4 or 5, Berkeley Alpha USB) and if so, in what environment using what equipment?
Here is my predicament.
Let’s assume that claims about more precise clocks in converters such as off-ramp are based on facts (and probably are, off-ramp clocks are most likely significantly better than the one used on ESI Juli@).
And let’s ignore the argument that I2S is the interface you want to use to connect to DAC in order to minimize the impact of jitter, let’s focus on SPDIF for those who do not have DACs with I2S.
Considering that multiple SPDIF conversions (on the side of USB/SPDIF converter or sound card and later on DAC side) will inevitably add jitter (usually it is measured in several hundreds of pS) that the DAC chip will be presented with, is there any benefit of using those USB/SPDIF converters with superb clocks IF you must use SPDIF?
My thinking is the following, let’s say you start with very low intrinsic jitter (~5pS), then transmitter adds several hundreds to place in on SPDIF output, then you add some line induced jitter, then add some on the receiver side, you end up with what, 500 - 700 pS on DAC? Do you benefit here if you start with 5pS vs. let's say 50pS?
Let’s leave “jitter rejection” techniques outside of discussion, they do not work, they only result in jitter artifacts embedded in the signal.
The dilemma here is, if you must use SPDIF do you see any real advantage with USB/SPDIF converters that use exceptional clocks? I do want to send as little jitter on SPDIF line to DAC, but I fail to see real advantage of superbly build USB converter like off-ramp over a well executed PC with good sound card, if SPDIF must be used?

To add further to it, when I look at jitter measurements made on off-ramp 4 and BDP-1 made by the same reviewer, off-ramp had 343 ps while BDP-1 had ~120ps more if I remember correctly, so it kind of goes in line with my predicament which is really the following, if I have to live with SPDIF/AES3, whatever the case may be, it all boils down to the same, because 343ps vs. 460ps is not something that will make significant if at all an audible difference. Avoiding all together SPDIF transmission would be a different story and the way to go would be clear, but under these circumstances not so much. Does it make sense?

[audioengr]

Considering that multiple SPDIF conversions (on the side of USB/SPDIF converter or sound card and later on DAC side) will inevitably add jitter (usually it is measured in several hundreds of pS) that the DAC chip will be presented with, is there any benefit of using those USB/SPDIF converters with superb clocks IF you must use SPDIF?

Absolutely.  Modern S/PDIF receivers do not add hundreds of psec of jitter.  I did the experiment with the Off-Ramp 5 driving my own Overdrive SE DAC versus the I2S from the same Off-Ramp 5. Both using excellent cables. They were audibly indistinguishable. 

If your particular DAC uses an older receiver technology such as the CS8412 or the S/PDIF input circuit is poorly designed, then the result may not be quite as good, but still stellar IME.

The result with S/PDIF has a lot to do with the cable used, for both USB and S/PDIF.  If you use a decent S/PDIF cable with the Off-Ramp 5, such as a 1.5m Ridge Street Audio Poiema, then S/PDIF will be killer.  A good starting point for USB is the Locus-Design Polestar. 

You can read multiple reviews from both customers and the press (TAS, Stereophile etc.)  that demonstrate the the Off-Ramp 4 or 5 driving a typical USB DAC using S/PDIF coax beats the built-in Adaptive or Async USB interface on those DACs.  This was demonstrated with dCS Debussey, PSAudio PWD, W4S DAC2, iDAC, VDAC, BelCanto 3.5 and others.  See these reviews:

http://www.empiricalaudio.com/news-and-reviews/off-ramp-converter

Other reviews are on this forum. Do a search.

And BTW, even my own Overdrive SE DAC is only slightly better using the built-in USB to I2S interface versus an Off-Ramp 5 driving it with S/PDIF.

Also, beware of RMS jitter measurements.  They dont tell anything near the whole story because they hide the spectrum and all of the spikes in the spectrum.  This is actually more important than one measurement that averages the jitter.  Comparing one RMS jitter to another makes no sense at all.  Rating one product against another using this metric makes no sense either.

Even JA could not measure the differences in jitter that he plainly heard using one cable versus another in the review of the Off-Ramp 4.  He said that even if there was a slight difference in 2 of the cables, the measurements favored the cheap cable, which sounded poor, and disfavored the expensive cable, which sounded good.  No correlation.

Steve N.

[art]

My thinking is the following, let’s say you start with very low intrinsic jitter (~5pS), then transmitter adds several hundreds to place in on SPDIF output.................

How on earth did you come to the conclusion that a SPDIF TX stage adds that much jitter? I have measured lots of products, and any with "low intrinsic jitter" do not add that much jitter. Even ones I look down my nose at.

(No, don't ask which ones I look down on. Let's just say they use a PCM270x. But, since they do not have low intrinsic jitter, it is a moot point.)

Sorry for the temporary interruption...........back to normal programming.

[bhobba]

How on earth did you come to the conclusion that a SPDIF TX stage adds that much jitter? I have measured lots of products, and any with "low intrinsic jitter" do not add that much jitter. Even ones I look down my nose at.

Art is correct - it does not add that much Jitter.  My experience as well is the spectrum of the Jitter is also important and the Jitter added by SPDIF is uncorrelated Jitter and not as audible - just conjecture of course.

Thanks
Bill

[Sasha]

Ok, if we do not see hundreds of ps added by SPDIF TX stage, where does the figure of 343 ps on off-ramps SPDIF comes from? What has generated so much jitter?

[art]

Probably what it is connected to, with the actual audio output.

[art]

Art is correct - it does not add that much Jitter.  My experience as well is the spectrum of the Jitter is also important and the Jitter added by SPDIF is uncorrelated Jitter and not as audible - just conjecture of course.

Thanks
Bill

Actually, it depends on the product. Some do have correlated jitter.

[Sasha]

Probably what it is connected to, with the actual audio output.

It makes no sense, the measurement is not done in such a way where something connected to it influences the result.
Unless someone can explain these figures that indeed measure in hundreds of ps on SPDIF on virtually all components ever measured, I do not see what else contributes to these numbers but the process of framing and transmitting data on SPDIF.

[audioengr]

It makes no sense, the measurement is not done in such a way where something connected to it influences the result.

I dont agree.  The termination and the cable etc.. of the test equipment change the result from that in the system.  They are different.

If you look at the spectral plots closely from the Off-Ramp 4 review you will find that the spectrum is cleaner than other USB converters and USB interfaces once the signal passes through a DAC, in this case the Transporter DAC and the dCS Debussey DAC.

Unless someone can explain these figures that indeed measure in hundreds of ps on SPDIF on virtually all components ever measured, I do not see what else contributes to these numbers but the process of framing and transmitting data on SPDIF.

What you must understand is that even clocks that are specified by the manufacturer at 5-10psec once in a system have jitter in the 100's of psecs.  There is really no way to stop this short of heroic measures, such as those used at NIST to measure small signals etc.. Cryogenics, microwave amplifiers, solid copper and steel shielding and really expensive power supplies, even superconductors.

Everything in the system adds noise and therefore jitter, not just the S/PDIF converters.

The relevent question is whether the jitter spectrum is audible when a DAC is driven with this USB source.  I feel that the Off-Ramp is the least audible of any USB converter or interface, and the reviews show this.

Why dont you just try one?  It has a 30-day money-back guarantee.  You are only risking the shipping cost.

Steve N.

[werd]

There are far worse non linearity issues from pre Amps and power amps to worry about then the analogue output of a dac. What ever jitter we get from a dac that would represent itself as distortion on the output would certainly be masked by the distortion from a well built tube amp (for eg.)

Thats my .02 on it.

[audioengr]

There are far worse non linearity issues from pre Amps and power amps to worry about then the analogue output of a dac. What ever jitter we get from a dac that would represent itself as distortion on the output would certainly be masked by the distortion from a well built tube amp (for eg.)

Thats my .02 on it.

You are certainly right about preamps.  The only one I will have in my system is a really good transformer linestage.  Active preamps are the worst bain of both digital and analog audio IME.  I took my highly modded Levinson pre out of my system once I had my Overdrive DAC and its a boat anchor now.

The only amps I will have in my personal system are highly modified too.

Steve N.

[art]

Since I did not make the measurements, and do not know the actual procedure, the most likely situation is there is a DAC, which has its jitter measured. If not, I do not see any way a single TX component can generate that much.

While I do understand why these sort of measurements are made at the audio output, as that is the only metric that matters, the way they are done is prone to lots of confusion. Most involve reading the sidebands, of some signal.

First, you have to know not only the numbers (like x pSec, or -y dBc), but also the spectral content. Then, to add confusion, the frequency of the signal is part of the equation. A fixed amount of sidebands will have lower jitter numbers, as the signal frequency increases. If one guy uses 11 kHz, and the next 16 kHz, trying to make a direct comparison is not possible, without knowing the fudge factor, to put both on equal footing.

So, even if you know all of this, does this still mean it makes any sense? The folks who design this stuff don't agree on what is more important than other matters. We have our believe that the sideband level has to be "so low", and that sidebands at "this frequency" are more harmful than those at "that frequency". But, that is just an opinion, and we all know how useful that is. There is not an absolute metric, cast in stone, that must be obeyed, and all else is crap. Nope, doesn't work that way.

Designers I know argue this stuff, back and forth, all day long. If we can not agree, how can the layman/customer? It is simple: you can't. Just take those nice plots, in the magazines, and take them for entertainment value. Trying to make sense of them is not going to happen. As a designer, we find value in them, but not for the obvious reason(s).

Steve has the right idea: buy something, and try it. Most folk have some sort of trial period. If it sounds good, buy it. If not, try the next guy. Leave the worrying to the professionals. We like have something to argue about.

We don't even agree on how to measure it, and what kind of equipment it takes.

[werd]

You are certainly right about preamps.  The only one I will have in my system is a really good transformer linestage.  Active preamps are the worst bain of both digital and analog audio IME.  I took my highly modded Levinson pre out of my system once I had my Overdrive DAC and its a boat anchor now.

The only amps I will have in my personal system are highly modified too.

Steve N.

I am moving more and more into low gain preamps. There is just way to much unnecessary gain presented in a lot of pre amps.  Especially now with source dacs out now that can drive a soundstage into an amp np....

[Sasha]

I agree on pre-amps, as long as they have any gain they color the signal.

I will try off-ramp as soon as the system is ready for comparison, but I like to understand why I hear what I hear and find a way to correlate what I hear with measurements.
It cannot al be voodoo science and based on trial and error, design of digital circuits is not alchemy.

[Audioexcels]

Absolutely.  Modern S/PDIF receivers do not add hundreds of psec of jitter.  I did the experiment with the Off-Ramp 5 driving my own Overdrive SE DAC versus the I2S from the same Off-Ramp 5. Both using excellent cables. They were audibly indistinguishable. 


Even JA could not measure the differences in jitter that he plainly heard using one cable versus another in the review of the Off-Ramp 4.  He said that even if there was a slight difference in 2 of the cables, the measurements favored the cheap cable, which sounded poor, and disfavored the expensive cable, which sounded good.  No correlation.

Steve N.

IMHO, it's all in the design.  Everything after that is subtle improvements to extract as much possible from that device.  It's not to say the improvement from a standard OR5 to one with the Hynes USB won't show a very nice level of sound improvement, but is to say the OR5 is already so well established as it is, that one can easily get most all the benefits from it as a standard/reference vs. anything else out there even in its stock form due to its intrinsically impeccable design.

[Audioexcels]

I don't agree about what has been said regarding an active preamp where the gain structure can make proper use of the signal.  However, if this additional gain (preamp) is not transparent, as most everything cost no object I have heard out there is not, you end up swapping loads of different preamps into your system until it is "flavored" how you want it=not a problem since audio is subjective and our ears may prefer flavor to transparency.  This said, best way to get to this level of transparency is as much of an all in one solution possible=Transparent Amp-precise gain for the amp-Dac-I2S conversion-Standalone device that can have a couple of USB ports for a Hard Drive and for times I would want to watch a movie with the computer;)...all short traces and anything inside like the PS that may be causing interference/noise/etc. housed outside.  Then I would only need speaker wire and a single USB cable (for times I wanted to connect it to the Computer).

[tpaxadpom]

I've measured several converters on AP2722 (same equipment JA from Stereophile use). I have not seen difference in jitter measurements (50Hz-100kHz range pk) using different USB/SPDIF cables, software players on MAC Lion and WIN7 bootcamp. On my to do list is to compare jitter spectrum but I don't think I will get anywhere with this. And yes I can clearly hear the difference between different cables/soft players.
PS: http://www.youtube.com/watch?v=s_Cma3cvD7o&feature=youtu.be here is jitter measurement of AP2722 using j-test pattern (looping BNC coax). BTW the same jitter was measured using toslink. Best converters I've measured had peak jitter about 3 times lower.