[art]

Lessloss thinks two-way clock signals (out from transport to DAC AND out from DAC to transport) riding the s/pdif cable is a major problem.  The clock frequencies do not mesh which further complicates things.  Their solution is to have the DAC clock output via separate cable to a transport with disabled clock.

Well, yeah. Hope they did not stay up all night thinking that one up. Oy vey.

Data stream only out the transport, clock stream only in.  It's an elegant solution which works quite well to my ears.

Elegant??????????? Try 16 years later than the rest of us figured out. The problem isn't doing it. The problem is getting people to adapt it.

Translation: Why do you think that we stopped making outboard DACs after only 1 production run? No one was interested in doing it the right way. Rather than "fight City Hall", we went back to building amps and preamps (only).

Pat

[miklorsmith]

I didn't say they originated the thought, how would I know?  There are lots of old ideas being dusted off and improved upon, see tubes and widebanders.  If there are neglected, good designs that can be brought back and furthered, I'm all for it.

[BrianM]

Can someone point me to an informative discussion somewhere of why SPDIF sucks so bad? I'd like to read all about it.

[NewBuyer]

.. I've wondered about ASRC's: Wouldn't jitter/timing issues received at the ASRC chip just get remapped to a different rate (i.e. garbage-in/garbage-out)? ..

Personally I hope the latest generation of soundcard/player-software combos, and also the essentially ethernet-dacs (with server software control) like the Transporter, SB3, etc will make permanent headway into the jitter-busting fight - since ethernet is pulse-transformer isolated, and since the ethernet device depends on its own clock instead of S/PDIF timing.

I have no idea what the answers are - just wondering what others think. 

...if you rcv a 44.1khz stream and convert it to 88.2khz. A sample value is held for 1/44100 of a second and during that time it is resampled twice to generate the 88.2khz output. Note, the clock used for output is different from the input so input clk jitter is not retransmitted...Personally, I prefer using a very good clock at the source, say in a squeezebox... main advantage with PC or devices like Squeezebox is that their electrical design is simple enough to reduce power supply related jitter.  (nothing to do with ethernet etc as you seem to confuse yourself with).

Hi AEA,
Thanks for your reply. However I don't see how just transitioning from one clock to another would cause jitter to not be transmitted. Doesn't that assume that at the second clock, the signal was received with proper timing (i.e. no jitter) in the first place. If the signal is received "off" in its timing due to signal jitter, the second clock will just receive the off-timed signal and re-transmit it again, perhaps at a different rate is all - am I incorrect here?
Also about the SqueezeBox advantage having nothing to do with ethernet, why do you say that? Using ethernet for data transfer means no S/PDIF transmission conversion (instead uses network data packets) and thus also allows having a very good clock local to the dac, rather than the dac having to depend on the externally received clock signal. As S/PDIF and its associated timing issues can be a major contributor to jitter, this certainly seems like an advantage to me (but certainly not perfect, as Art explains). But I may be missing things here - please let me know if that is the case.

[TheChairGuy]

I thought jitter was already reduced to the lowest levels now...below the threshold of audibility for all of us.  Does it still matter - or is this just chasing audio fairies 

[low.pfile]

Can someone point me to an informative discussion somewhere of why SPDIF sucks so bad? I'd like to read all about it.

I am trying to understand myself. There's lots of subjective writing in hifi/audio.  I think that pro-audio covers the topic the best. something I came across: http://www.soundonsound.com/sos/jul99/articles/pcmusician.htm   I would like to see testing that compares bench measurements of jitter vs. a listener's hearing perception. But for now I leave it just to what sounds decent without letting data interfere with my music listening enjoyment. There are so many other variables in an audio system.

[art]

Can someone point me to an informative discussion somewhere of why SPDIF sucks so bad? I'd like to read all about it.

No, but here is something that some of you can try in your very own home. And then you can draw your own conclusion.

Take the lid off of whatever SPDIF DAC doo-hickey that you have. Find the RX chip. (Usually made by Crystal.) Find the pin where the PLL filter components are. It will be a R-C, or R-C-C network.

Ok, things get a tad tricky here. Some of you won't be able to do this. Find a nerdy friend who can.

You will need some sort of battery-operated amplifier, that can drive a headphone directly. Something made with a low-noise op-amp........like.....AD797 would be fine. Set it up for......I dunno........40 dB of gain.

Now, connect this headphone amp thing (oh, it should be AC coupled, btw), and listen to the noise on the PLL filter pin.

"Hey, it just sounds like some nasty noise. Why did I let you talk me into trying this? This sux, what a waste of time."

Ah.......not so fast, skippy...........

Now hit the "play" button on the CD transport driving it.

Tell us what song you are now hearing. (Hint: it will be the one that the transport is playing.)

Enjoy!

Pat

[BrianM]

Tell us what song you are now hearing. (Hint: it will be the one that the transport is playing.)

Yeah, so?  For those of us who can't try this experiment at home, I take it you mean we'll hear how noisy the PLL thingy is.  To what degree is this related to what we hear coming from our speakers?  If I could hook headphones up to the power transformer of my amp, I suspect it would sound pretty noisy, too, up close.  I don't have a beef with your illustration, I just don't know what exact conclusions to draw from it.

[darrenyeats]

why do you say that?

I believe APhileEarlyAdopter's point is that if the SB3 is used as a transport, then it's going to have the same jitter issues as a CDT except no moving parts, servos etc, which means less electrical noise.

NewBuyer, you are correct that a computer network introduces no jitter. (I don't think APhileEarlyAdopter's point conflicts with this.) If the SB3 is used as an all-in-one player it has the same advantages of avoiding S/PDIF jitter as an all-in-one CDP...except no moving parts, servos etc bla bla same point again but this time hopefully helping the DAC and analogue circuits.
Darren

[NewBuyer]

...Personally I hope the latest generation of soundcard/player-software combos, and also the essentially ethernet-dacs (with server software control) like the Transporter, SB3, etc will make permanent headway into the jitter-busting fight - since ethernet is pulse-transformer isolated, and since the ethernet device depends on its own clock instead of S/PDIF timing...

...Actually, main advantage with PC or devices like Squeezebox is that their electrical design is simple enough to reduce power supply related jitter.  (nothing to do with ethernet etc as you seem to confuse yourself with).

...I believe APhileEarlyAdopter's point is that if the SB3 is used as a transport, then it's going to have the same jitter issues as a CDT except less moving parts, servos etc, which means less electrical noise.

NewBuyer, you are correct that a computer network introduces no jitter...

Well that's better then, since in my post I had clearly referred to using the SB3 as an essentially ethernet-DAC (and was thus not referring to using it solely as a transport). I believe the main advantage of the "ethernet-dac" style approach is not just simpler power supply requirements (after all, lots of standalone S/PDIF DAC's have equally simple power supply requirements). Rather, the major advantages are the decoupled RJ-45 interface - and that the harddrive/ethernet connection allows the DAC chip to rely solely upon an excellent local clock for signal timing, instead of depending on the jittery S/PDIF external clock recovery scheme.

However, any more general claims about the PC approach somehow having jitter advantages due to simpler electrical design are potentially misleading, since a particular PC's ATX switching power supply could cause a soundcard's S/PDIF I/O to have more interference and jitter, than that from a conventional (non-PC) standalone transport - even if the PC is using an absolutely top-shelf soundcard. The decoupled and localized-clock design of the harddrive/ethernet-dac approach is conceptually much superior in my opinion.

However, I do like using the SB3 as a transport too - so I'm interested in whatever Art has up his sleeve...

[Ethan Winer]

I didn't think jitter was a noise issue quantifiable as dB below signal, rather a timing error OF the signal.

My reference is Ken Pohlmann's Principles of Digital Audio which is considered by many audio engineers to be the bible of this stuff. His graphs show jitter typically 120 to 140 dB below peak level, and expressed that way as dB. Yes, you can express it as a timing error, which is what it really is, but as Pat explained it shows up as FM sidebands at some dB level.

This is how Stereophile explains what jitter is actually doing.

The problem with those charts is the jitter is exaggerated about a million times - literally - to make the point. I can show that eating broccoli is very bad for you if you'll agree to eat 35 pounds of it at one sitting.

I must point out that talking about jitter and what is and is not audible is meaningless without specifying amplitude, frequency spectrum, and level of data-corrleation. Random-occurring noise is much less noticeable than jitter that is data-correlated.

Yes Pat, but if the artifacts are 120 dB below the music it's simply not audible whether it's random or correlated.

A whole branch of industry (building transports, reviewers and DIYers) cannot be a bunch of charlatans or deluded.

Why do you believe that? If a normal amount of jitter is inaudible, what is your better explanation? Please be very specific!

I don't think anyone doubts the existence of jitter as a measurable phenomenon.  The disagreement is over how important, relevant, audible it is.  Building transports and DACs that attempt to address jitter doesn't have to be charlatanism, but it might be gilding a lily.  Lots of businesses promote "advancements" before there's universal agreement as to their benefits.

Give this man a ceegar.

Finally, I repeat yet again that human auditory perception is incredibly frail, and often we believe what we want to believe. That, plus comb filtering as explained in my article linked earlier. Not sure if any of you caught the recent news item about expensive placebos versus cheap placebos:

http://www.scienceagogo.com/news/20080204181613data_trunc_sys.shtml

Note that the reported improvements in both cases were due to placebos!

Those here who believe they can discern reduced jitter are most welcome to visit me and be tested blind. I have $100 for each and every one of you who can reliably pick out the difference. I am absolutely serious. Bob? Anyone else near me in Western CT?

--Ethan

[woodsyi]

Ethan,

I am going to be in Monroe for a St. Patrick's day party Saturday.  I can swing over on Sunday.

[art]

And are you going to send me $100 for every one who can? How are you going to reduce the jitter? Who sets the metrics for that? Who decides whether your "jitter reduction method" is valid.

(I suppose one good way would be to have a SPDIF DAC that has a secondary PLL/reclocker that can be switched in and out.)

I charge $70/hour, but I don't travel. You are free to come to Texas. Bring your $100.

BTW, I can also show how digital cables affect jitter. Bring an extra $100.

BrianM:

The clock should be "perfectly" quiet. The sound/music that you will hear is modulating the clock, because that is what you are hearing.

You asked where you can read up on SPDIF. I don't have a bibliography at my hands to show you where to look. Instead, I provided an example of why we came to realise it is so bad.

The fact that you can pick out the music that you are listening to is an example of data correlated jitter. That is what makes SPDIF so bad. The method of extracting the clock contains modulation artifacts that is strongly dependent of the programme source. It shouldn't be.

That is why companies have gone to things like ASRCs, to clean up that modulation.

My company has not made any products in that realm, for at least 15 years. So, anyone who thinks I am here to sell stuff, well, it hasn't existed for a long time. Yes, I do consulting. I sell "concepts" to other firms. Whether they actually use them after I get paid for my efforts, well I have no idea. I get paid to come up with them and keep my mouth shut about it afterwards. I am not getting rich in my effort to bring some sense to the jitter debate. Any one who does not want to believe how much of a problem jitter is (pretty much confined to the SPDIF world) is free to dismiss them. Just remember: I'm  not selling a product or making money by spending my time explaining this. I do it because I have the experience to discuss this without the usual snake oil effect that a lot of audio has.

Sometimes there is a rational explanation to some of the mysteries of audio. It just seems irrational.

Pat

[KBK]

I've explained in threads that Ethan (if not ,Ethan, I apologize - but he may have read them) has been involved in, on the Stereophile forum, of why Jitter of such low values is heard by the human ear. All the math is right there, for those who wish to investigate it (the basics of the math 'path' to show that it exists -and it is real). The same explanation is also why a given audio frequency cable has to be nearly astronomically 'perfect'.. from DC to light speed, or from a proper DC to at least 1Mhz, and with any intermixing of 'loading' of any kind.  Designing such a perfect cable is nearly theoretically impossible and....with respects to actual construction, practically (real world) -- impossible. All are a compromise of some sort.

The same applies to digital circuits, which also 'load up' ('micro transient AC current draw' wise) differently according to what exact kind of signal they are dealing (manipulating/converting) with..thus creating their own 'repeatable' jitter characteristics. The given chip sings along with the music in a specif repeatable micro jitter pattern. Micro processors are quite guilty of this. ADC and DAC are far simpler circuits generally, but are still quite guilty of it.

The same information is also why cable elevators also play a part that is noticeable by the human ear. Same for molecular considerations at the molecular 'noise' level. If you think that is bullcrap, go to your latest Digikey catalogue and look at the surface mount resistor section. In there you will find a descriptive of a well known company who goes on and on about this specific aspect of it's resistive materials and now 'noiseless' they are, compared to the rest of the products out there.

One has to go and look at the mechanism of how the human ear works to get a handle on this stuff.

Just remember ignorance is the thing that precedes knowledge or truth. Wisdom is what you do with it, and then, hopefully what you use the next time ignorance comes around in your life.

Many times, companies who have engineers and owners who have such knowledge and wisdom to further the art of audio..have to keep such knowledge to themselves, as that is key and core to their capacity to create products that differentiate them from the rest of the herd. Publishing that information is a loss of leadership or position in the market. Actual loss of income.

Differentiating between the groups of those who know... and those who are poseurs...is a bit of a problem. The standard human reaction to a problem in a unknown area where enlightenment is searched for..is frustration and anger. Heated emotions. Especially when 'standards' and established positions are threatened. Remember the rule about ignorance coming first.

It's how you attach yourself to the idea of ignorance..and what you do with it... that separates the men from the boys, the humans from the talking monkeys. Pause, consider, investigate. Ie, effort.

The point about jitter in ADC and DAC, is that very low level of jitter..is attached to the PEAKS of the signals, the transient edge..and that is all that the human ear works with and operates by. This then leads to an understanding of the importance of micro ripple in current delivery systems. And then on to the rest.

[Ethan Winer]

I am going to be in Monroe for a St. Patrick's day party Saturday.  I can swing over on Sunday.

Do you mean next Sunday the 16th? I can't do it that day, but every Saturday and Sunday after are available. Let's you and me pick another weekend afternoon, and anyone else who's up for it the same day we pick is welcome to visit too.

--Ethan

[Geardaddy]

Those here who believe they can discern reduced jitter are most welcome to visit me and be tested blind. I have $100 for each and every one of you who can reliably pick out the difference. I am absolutely serious. Bob? Anyone else near me in Western CT?

--Ethan

Ethan, I think that is a great idea.  If I lived in closer proximity, I would totally play ball.  The placebo phenomenon is a powerful reality.  I am not an engineer but do inhabit the biomedical domain and know that any study worth its salt has to control for that variable.  There have been studies using PET or SPECT of the brain that demonstrated increased blood flow based on an item's price.  There are also fields of study being generated from this, including "neuroeconomics," etc....

Anyway, it would be a fun experiment to correlate jitter measurements (with an externally validated tool or not...) with sonic perceptions in a blinded fashion using audiophiles and non-audiophiles, etc.

p.s.  As a disclaimer, I am not a cynical reductionist (read BF Skinner) who views human beings as bags of chemicals subject solely to external manipulation via sense data.  There is something beautiful, transcedent and dare I say religious behind the audiophile pursuit....

[art]

Many times, companies who have engineers and owners who have such knowledge and wisdom to further the art of audio..have to keep such knowledge to themselves, as that is key and core to their capacity to create products that differentiate them from the rest of the herd. Publishing that information is a loss of leadership or position in the market. Actual loss of income. nvestigate. Ie, effort.

Excuse me, but I made an entire thread, full of measurements, showing exactly what was done and how. If I left off a few minor details, like how I come up with the resistor values used, well, yes: showing what I get paid to do and then giving it all away for nothing to a group of DIYers would result in a loss of income. None of the manufacturers that use my services would be likely to do so again.

Having said, that I have given more useful information on these subjects than the charlatans that take $20 supplies from Mouser, and stick some $100 gizmo on the "gosinto" and  gosouta", and charge $$$$$$$$$ for it.

I hope that comment was not aimed at me, as it is way off base if it is.

Pat

[KBK]

Many people can do the jitter analysis, but it has to be in systems they are intimately familiar with. Not ad-hoc shots in the dark. As well, the stress components must be removed from the 'contest'. Ad-hoc, unfamiliarity and stress being critical factors. Then the test becomes valid.  Remember the point about ignorance. The test must be valid as well, it must take into account all the pertinent factors. One of them is the humans attached to the test.

No comments were specifically aimed at anyone. That would be ego, and I'm not generally prone to it. Which is why I can blunder into situations where I seem to enrage others. As Spock would say..."I fail to see...."..and Bones starts yelling at him. Then Spock wanders off all confused.

[Geardaddy]

Pat, if it was directed at you, it is WAY off base.  I appreciate you taking the time to inform and educate nimrods like moi....

[Ethan Winer]

And are you going to send me $100 for every one who can?

Heh, nice try. The $100 goes to those who can reliably identify jitter.

How are you going to reduce the jitter? Who sets the metrics for that? Who decides whether your "jitter reduction method" is valid.

I'll be glad to let you have a say. I tested this recently by playing 24-bit music files through my Delta 66 sound card using its internal clock and then clocked by a $6,000 Apogee A/D/A box. We also compared the same file played back through a $25 Soundblaster card. (The fellow who brought over his Apogee was unable to hear a difference between the three setups.) Even easier, and probably better controlled, is to use test files from Arny Kruger's PCABX site. We can play files with increasing amounts of jitter added artificially, and identify at what point the jitter is audible. If you have other suggestions, I'm all ears.

You are free to come to Texas. Bring your $100.

Sorry, the test will be done here in my two controlled and well-treated listening environments.

BTW, I can also show how digital cables affect jitter. Bring an extra $100.

I'm sure it can be measured if the cables are long enough. That's not the point. The point is if it can be heard and reliably identified by ear. We can easily measure 0.01 percent distortion versus 0.001 percent, but that can't be heard either.

--Ethan