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In Reply to: RE: Jitter Research, Analysis & Measurement posted by Sunya on March 25, 2008 at 23:22:25
I shared your same ideal view, ie. optical input and DAC (or external clock) as master. Thats why I bought the Scarlatti Clock.The clock of the soundcard can't be as good as the one generated by the DAC, not to mention the PC environment isn't exactly helping.
In the paper, following is mentioned:Computers superiority in jitter performance is not well understood. Consider this: SATA specifications demand strict jitter tolerances for which standards are defined (something like not exceeding 160ps peak). Computer manufacturers utilize jitter testing equipment measuring in femto seconds (a femto is a thousand fold less than a ps)! This is all very necessary to achieve very high bandwidths and extremely low bit error ratios.
Computer manufacturers have substantially more R&D dollars to create faster, cheaper & more efficient products. Because of ever increasing performance demands (faster processors, RAM etc) manufacturers have to reduce jitter to very low levels. This is critical for achieving high bandwidths. Clever noise reduction technologies are being implemented, e.g. DDR2 that has ODT (on die termination) technology that terminates signal reflections within the memory module. Reduction in power consumption demands is also forcing the industry into creating low-power components.
Combining a soundcard (PCI, Firewire or USB based) with a computer allows one to achieve low jitter when correctly optimized. My experience suggests that soundcards have good quality XOs (a must for the recording industry where computer audio is the norm). Yes, computers are complicated animals and offers phenomenal capabilities BUT they come with configurations that suit a general PC user and NOT audio. Such configurations create lots of jitter at the soundcard. The challenge is in reconfiguring it.
Thus, a computer acting as Transport is a perfect platform for low jitter IF configured correctly. Given its processing capabilities it offers another very important benefit: high precision upsampling based on bandlimited interpolation which recreates the analogue waveform. Such reconfiguration of a computer is covered in cMP's documentation (based on Windows XP). Others provide excellent guides for Linux. When fully implemented, the results are very good indeed. So much so that it can act as clock master and question the 'DAC as master' approach! You get all this for $1500. That's how I'm experiencing it and feel compelled to share it.
Sound cards all have very jittery clocks IME. The computer has little or nothing to do with it either. I have evaluated a LOT of different clocks, and found only two that are acceptable to me. One of these is the Superclock4.
The reason that there are superior computer audio solutions to CD players is that the chips available for USB have superior digital PLL's in them. If CD players had minimal buffering and good digital PLL's they would be equally as good.
Wi-Fi has a distinct advantage because the data is networked and packetized. This allows the master clocking to occur at the destination, independent of the source.
If you are looking for really low jitter solutions, spending money on really expensive gear may not get you there. It's making the right choices.
Steve N.
Hi SteveN,
What is the other clock you found acceptable - hope it's lower cost than the Superclock4?
Do you think that 90% of the improvement in putting on a new clock is in the new cleaner/better PS that feeds the clock? If not 90% what figure would you put on it?
The other clock is a trade-secret.
Power subsystem, not just power supply makes a big impact on the superclock and other logic performance. Also the board layout and circuit board layout and design as well as transmission-line terminations and impedance matching also have a big effect. It takes all of this to achieve a really low system jitter.
Steve N.
Trade secret? Why? Is it not commercially available? Is it some new product?
Why not dispense with all this clock business nonesense & go for the ESS Sabre Multi-channel DAC which recovers the clock from the SPDIF apparently without jitter. How its' done is a trade secret but at least it is available!
Apparently? Yeah right, I've heard this before.
Why would I buy another DAC when my own design beats everything I have heard? Only Zanden 5000 comes close...
Did you had the chance to see the Stereophile measurements for the Zanden 5000? There were performed 2 measurement sessions because the manufacturer claimed the first sample was defective. Check the jitter figures on both samples, it really seems like overpriced junk in a shiny box targeted at clueless rich guys...
first sample measurements:
http://stereophile.com/cdplayers/1106zanden/index4.html
second sample measurements:
http://stereophile.com/cdplayers/1106zanden/index8.html
Just because it has high jitter does not mean that it necessarily sounds bad. The jitter spectra could be inaudible to most humans. I have customers with this DAC and they tell me is is very good. Sometimes musicality is more important than detail.
How do we measure musicality?
With our ears, in stereo.
Electronic instrumentation and classical measurement techniques are not able to do it IME. It will take a multi-dimensional measurement to do this I believe, including phase, magnitude and frequency for two channels in a two-dimensional plot. This plot will also need to be swept over gain settings so that compression due to absolute level can be observed. Nothing like this has ever been done to my knowledge.
Steve N.
Have a look over at DIYA - design engineer has been posting & sending out sample boards - so it's not marketing hype as before - it is standing up to the claims made of it!
Why the trade secret clock - you didn't answer this?
Of course I didnt answer. It's a trade secret. We manufacturers have to have some of these otherwise our competitors just steal everything and put us out of business. Patents I have lots of. They are worthless unless you are willing to spend $100K in court.
I guessed as much about your post - all smoke & mirrors ("trade secret") - just a lot of bullshit being passed off as mystique - unfortunately, a common problem in this area called HIFi!
Good to see Stereophile expose some of the pretenders, whoever they might be!
My products speak for themselves. It's all about the engineering. I'm an engineer with 30 years design experience. I dont ever lose in shootouts.
OK, I didn't realise you were a manufacturer - then it's understandable that you protect your IP, I agree.
It also explains your reaction to the ESS Sabre DAC I mentioned!
They dont allow me to identify myself on this forum. Against the rules.
If you use Superclock4 as a reference, then soundcard XOs would be poor.
Dunn suggests jitter below 20ps is inaudible. I'm using this as a reference for which professional soundcards can be compared to.
I dont give a hoot what someone suggests. In a highly-resolving, low-noise system you can easily hear the difference between the Superclock4 and a Superclock3 for instance, and they are both probably sub-100psec in jitter.
Steve N.
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