Jitter

Jitter is probably blamed for bad sound too much, when it isn't to blame, and when there isn't actually bad sound.  Jitter as high as 10nS has been shown to be inaudible.

Anyway, I've always wanted to measure it, and now, with my Sencore DA795, I can.

Unfortunately the Sencore doesn't show numerical values below about 200pS, it just says "Low".  Most of what I'm reporting now is just from watching the logarithmic scale meter, which has markings at 100pS and 200pS.  So I'm reporting highly approximate values.

For the Pioneer PD-75, I see about 150-180pS jitter when playing a CD, which falls to 110pS when stopped.  Looks like some room for improvement in the power supply.  However even 180pS is typical for the best equipment ever made.

For my newest Sonos Connect, I measure 180-220pS jitter, clearly a bit higher than the PD-75 and more variable too, measured at coax spdif output.

(BTW, these are the RMS measurements.  The Peak measurements are over 500pS and very unstable, but the Pioneer is about 40pS better there too.  Also these are all unweighted measurements.  I have no idea how the Sencore measurements would differ from those using J-Test for example, but for sure the Sencore is completely insensitive to jitter in the recording.  It is only looking at the clock that can be recovered from the data, not the data itself.  I suspect John Atkinson uses a J-Test derived weighted peak number.  It's beginning to look like my unweighted RMS numbers are lower, but only about 50%.)

In both cases I used 7 foot Belden RG6 with Canare RCA's as interconnect to the meter.

In their original report, Stereophile reported 388pS jitter for the ZP80, which John Atkinson characterized as Excellent.  I thought that they showed 220pS in a later test, but I have been unable to find that.  In the 388pS test he's using J-Test on the analog output, you would think that to be comparable to the digital outputs.

I'm surprised that a heavy old mechanical device like the PD-75 actually beats Sonos on jitter.  But both numbers are excellent actually.  I would begin to feel worried with jitter above 500pS.  Some of the very best audio devices have jitter around 150pS, and often higher.  I'm not sure if I've ever seen jitter below 100pS for an audio device as such, though external clocks can have jitter spec down to 1pS or below.

Well, even assuming my meter to be perfect, there are 3 sources of jitter measured in the timing of the digital output:

1) The clock jitter of the pioneer, and everything that may ultimately affect the clocking out of data at the SPDIF output.  Audiophiles obsess over things like lack of power supply regulation for the transport section (which may be on a different transformer in this unit anyway) affecting the regulation of the clock.  And so on.

2) The cable losses and smearing (I proved this to be a negligible factor by seeing no difference with a far longer cable connected).

3) The jitter made inevitable by the coding of the spdif signal and practical transmitters and receivers.  I do not believe the clock can be perfectly recovered due to the nature of SPDIF data.  That is why the meter specified range only goes to 150pS with SPDIF input.  It goes to 35pS with a pure clock signal at the clock input.

3a) This varies depending on the actual data.  The Dunn test is worst case for 44.1/16.  Most music is less.  A continuing silence would probably be the least jitter, and for that reason I may record a test case.  I love being able to make my own test recordings btw.  Is this possible at low expense with DSD?  I can't make an SACD for 9000ES but I could apparently make a test disc DSD-File or something like that for my BDP-95.

3b) The actual properties of the Pioneer SPDIF transmitter circuit may also be a factor, say compared to a "perfect" implementation, perhaps an over-implementation.  I already set the baseline at "practical" and presumably the Pioneer isn't at that level perfectly, it may not be as good as something could practically get (say, without an Apollo Project--that's impractical for this) in impedance or risetime, for example.  I imagine some obsessing over such things (and even seeing me writing about them think I obsess over them either...no to my casual observers, I merely pointed such things out, unlike say Lampizator I'm only unsure of how important they are in the overall picture, but I'd expect a Pioneer Reference player like the PD-75 to do a pertty good job already at the powering the SPDIF output, and so it seems too, but who knows, it might be 2pS better with a bigger FET running more ten times more current at the output, on it's own separate transformer of course, blah blah, modifier believe they can may everything better).

What is that "minimum" jitter for SPDIF?  I need to read Dunn's articles.

Toslink out!,  AES/EBU vindicated!

I didn't think this was going to be hard.  Several times this week, usually just before going to bed (already way too late), or going to work, I was tempted to hook the jitter meter right at the end of the Glass Fiber Toslink cable I have connecting the Behringer 2496 DEQ to my Audio G_D DAC19.  This would show the evil Toslink jitter, which I didn't imagine to be very bad--especially with such a good cable--and actually the whole system jitter right at the critical point, the DAC for the panel speakers.  And the whole system is what many people consider complicated, many different boxes connected by digital cables that are mostly AES/EBU, including splitters, converters, EQ's, and a digital preamp.

Finally on Saturday night I was determined to do the measurement.  This would be almost worth the price of the meter, it's what I got the meter for!  (Well, actually among many other things...)

And there were SNAFUs right from the start.  It's as if fate itself did not want me to make this measurement.  First, I discovered my DA-795 meter doesn't accept Toslink inputs to the Jitter test.  It's not really clear because it allows "SPDIF 2" and the Toslink input seems to be on the SPDIF 2 side.  I was also maddened by the fact that I couldn't just select Toslink, and I figured that was the problem, that I had selected SPDIF 2 but needed to make some further selection related to the dozen or so icons at the bottom of the page to specifically enable Toslink.  I tried some of those to no avail.  I tried some other test functions and some of them did enable the Toslink input, but you often needed to have an additional input also, such as for the Transparency test where it compares one stream with another.

Finally, I brought up the manual on my computer and sure enough the Toslink jack that was seemingly on the SPDIF 2 side is specifically identified as being a SPDIF 1 input, and the Jitter test ONLY works with SPDIF 2, either coax or AES/EBU.

So the meter maker wimped out!  They didn't even want to try to let you see the Toslink jitter, for possibly the meter might be blamed!

So I determined to find another path.  So I removed the CO2 toslink converter on my Mac Mini along with its AC adapter and a short cable.  I would do the conversion from Toslink to Coax myself, using a converter which has proven itself time and time to be the best, and perfectly reliable.

Fortunately it's much easier to work on this stuff now that the living room floor back around the DAC is at least partly accessible.  But not perfectly accessible, it still requires trick kneeling and leaning on things and so on, all very carefully so as not to damage anything, including especially myself.

But as I was setting up the CO2, every time I nudged the AC power cables toward the wall, I heard something that sounded very weakly like sparking.  Then I just rotated the big 3-way adapter plug in the lower position of the super heavy duty Pass & Seymour Spec Grade outlet, and my UPS started running on backup power.  I played with this only a second time before panicked, I shut the digital equipment off, I shut the UPS off, and I unplugged the big 3-way adapter plug from the wall.  My girl friend had asked me if the big 3-way adapter was OK at least once.  I had actually asked my electrician about changing the two outlets to 4 outlets and he said it was possible but that was months ago.  An alternative needed to be created Right Now!

So this was another emergency project.  I would not operate my system again until it was safe!  I decided to plug the UPS straight into the wall, then plug the subwoofers into the TV power strip which was right there, and unplug the TV and a TV adapter to make room for those plugs (there are no spare outlets in any of the strips--this is the usual situation).

Now by this time the Jitter Meter had clicked off because of low battery, so I had to put it back on charging for a half hour.  Another delay.  But I was determined!!!

So then a half hour later I see that the Jitter Meter doesn't show any battery indicator like it's supposed to, but it runs OK on battery power, so I'm finally able to set up my test.

And I'm not getting any digital lock!  I reconnect wires, fiddle about, nothing.  Finally I notice once and awhile the jitter arrow shows up at about 500nS for a split second, then disappears.

So then I tried using coax instead of Toslink, but this was complicated because the DEQ's only have Toslink and AES outputs, nothing for Coax, and I haven't seen my AES-to-Coax adapter in years.  So I reclaim the adapter that was currently (and now previously) in use creating the coax line for the supertweeters.  I connected that to the midrange DEQ, and got a short coax cable to measure the jitter at the end of.

So now finally I'm getting lock and jitter measurements.  What at first I see is a bit troubling, the jitter playing a CD on the Pioneer PD-75 being redigitized to 24/96 by the Lavry and through my system (I figured the Lavry clock was about as good as it gets...and that's basically driving all the downstream clocks, so this should be nearly perfect and it has always sounded wonderful) was showing around 500pS jitter.

Then I try switching the digital input to Sonos, and I'm seeing only 280pS jitter.  That's not to bad for a whole pile of boxes connected to Sonos which itself measured about 220pS jitter.  All that extra stuff is only adding about 60pS more jitter.

So then I reset the Lavry to 44.1kHz, and the jitter is now only 290pS, just a tad worse than Sonos.

Playinng non-silence through the Lavry at 96kHz was showing about 380pS jitter.

I find this all to be quite signal dependent.  Digital silence is low jitter, classical music medium, hard rock somewhat higher, and background white noise (the -118dB noise of the Lavry itself) reads very high jitter like that 500pS I saw originally at 24/96.

Perhaps the Lavry show was showing a tad more jitter at 44.1 because the program was slightly different, or because the Lavry itself uses the lower bits more effectively.

Anyway, I'm not going to let higher jitter dissuade me from using High Rez!  I think the Rez is more imporant than 100pS more jitter, which may be averaged out by the DAC anyway.

Also, I'm not going to be planning to use Toslink any more.  My very complex system yields what I now consider surprisingly low jitter using only coax and mostly AES.  Only a tad more jitter is added because of all the complexity of AES DSP units, mostly the jitter seen is mostly only what was present at the source.

All my AES splitters and converters have now vindicated themselves, and I'm getting a second HOSA AES to Coax converter.  Meanwhile, the one unit I have is working for the panels and I've run Toslink to the supertweeter DAC which is less critical I think (can hardly be heard anyway).

My high rez line from the kitchen has always used 2-stage Toslink reconversion, because that is the only practical way to run this from my Mac to several devices.  I wrote about this here years ago.  Now I don't consider that suitable for high rez and I've ordered a New In Box Logitech Transporter.

When I saw the review for the Transporter in 2009 I regretted having gone with Sonos, but still at $1999 it was too expensive I thought and I didn't need much of the functionality, such as the analog outputs, and I would like other functionality, such as analog inputs to be available on the network as Sonos does.

I've had alternatives for handling high resolution discs, but my alternative for high rez files was through the Mac Mini and the dual toslink connection, which I now know needs to be avoided.

With the Transporter I get local control with a remote, no need to buy and maintain a separate computer, and now at the $588 ebay price reasonable.   A more up-to-date system like Sonore would require a new USB DAC...  But I don't want USB!  Or a computer in my living room, constantly crying for updates and maintenance.

Transporter is essentially a little stripped down AV computer which can do a bunch of things, including selecting the music to play, playing it, and putting out analog or digital in AES or Coax.

Of course it won't do DSD (directly anyway, without buying another gizmo, a DSD DAC which can accept DSD over SPDIF).  I don't care about DSD64 files anyway, I don't think I'd ever want any.  But DSD128 has some promise.  I could get a Pono to play those, and get them redigitized through analog at 96kHz, which is basically what I have to do with all DSD files since I have DSP based crossovers.  Maybe tomorrow.  I had been thinking about getting a Pono all week, but the Logitech was more mandatory IMO.