Digital Interconnects

Hi,

They do make a difference, for many reasons.

Unless your Kit has BNC connectors and is corrctly designed for 75 Ohm Input impedance (practically nothing is) the most important parameter is the length of the cable.I personally tend towards very short cables.

If you can stay in the 10"-12" long region the cable is short enough that with high quality coax cable (eg Maplin sourced FT/CT-100 with decent low metal content RCA plugs) with good propagation speed the reflections arrive quickly enough to not mess up the leading edge of the signal.

If you cannot be very short it becomes essential to be very long. You need to make the cable long enough that any reflection falls outside the trigger window of the receiver, usually that menas around 2 - 3m much depends on propagation speed, in effect you need to "tune" the cable length, preferably with a high speed o'scope in attendance. I find this hard work and therefore go for short cables.

Any other issues are very secondary if not tertiary, BUT if the cable has the wrong length (eg. the common 1...2m) the unavoidable reflections in the system fall within the trigger window and different cables can sound very different, simply because they make a large difference to the jitter levels.

Ciao T

 

The £70 Stereovox jobby got a very positive write-up in Hi-Fi+.

TBH, even if it makes no difference, I'm sure you could eBay it for £45. Not too much damage to the pocket IMO.

DT

 

Just bear in mind that Stereovox is best for smaller scale music and is a bit lean. If you need some additional control over bass it'll do the job. Straight from the box it disappoints, just be patient for a week or two.

 

As Iv'e done for a couple of members of this forum, I will make up a high quality true 75 ohm cable with Eichmann Silver Bullet Plugs and WBT Silver Solder for what they cost plus a beer which equates to £45 inc postage. Any length up to 2m for this price!

I use these in my Tag McLaren system and they absolutely blow away my previous digital cables from Nordost and Audioquest!

If anyone is interested send me a PM.

 

3Dsonics how do you come to a measurement of 1-2m? What formula are you working on?

 

Thanks for all the feedback and interesting debate most of which was above me but thanks anyway....
I have just managed to get a Kimber Kable Illuminati D-60 digital interconnect off Ebay for £49.00...as it retails for £164 and seems to have good reviews I have to assume I have done the right thing.
If I haven't I am sure I can sell it on and get my money back.....
I will let you know... it arrives on Thursday and I will also have the Chord Anthem ic's and Odyssey 4 speaker cable.
I hope these upgrades makes a substantial improvement to things!
paul

 

Hi,

First, 1 - 2m are common length for S/P-DIF connections (AES/EBU too), I do NOT recommend them.

The calculation is a bit complex.

You need to determine the trigger window for the receiver and the rise time of the signal (I had this somewhere, need to dig it up, no time in the next week).

Then you need to understand what happens when a reflection occurs due to poor impedance matching (using RCA sockets will screw this up even with "75 Ohm RCA Plugs").

As long as the reflection arrives either within the rise time of the signal (meaning with "fast" cables, that is a high percentage of lightspeed, 10-12" length max) or much after the rising/falling edge of the signal has passed it will not be able to effect the triggering of the receiver. This means you need either very long cables (but not as long as to delay the roundtrip of the reflection so much that it interferes with the next edge) to delay the reflections or very short cables to keep the reflections "in time" with the triggered edge.

I once did the whole math and figured you needed to stay below 12-12" or above around 2-3m (exact figures depend on receiver, signal levels and cables propagation speed) in order to keep outside the trigger window.

The alternative is of course to make sure that all connectors and cables as well as source and receiver are fully impedance matched.

A significant advance is possible if we use what I'd term an "active" cable, which is one that contains a termination and sending j-fet buffer directly in the RCA plug and with a standard twisted pair (Cat 5 network cable) absolutely accuratly terminated on both ends carrying the signal (remaining pairs can carry supply voltages etc).

At the receiving end add a Video Op-Amp to boost the signal to AES/EBU levels (all receivers are set to trigger best on these) and send this 75 Ohm signal into the receiver via a minimally short signal connection.

This way mismatches at the source and receiving end matter FA and the rest you have under tight control and you can make it as good as you will.

A corollary involves extracting the clock from the S/P-DIF signal directly at the source and applying a really slow PLL to it and to then send the clock and data down seperate wires and to re-clock the signal going into the receiving unit.

All a lot of doodaah that is too much hassle for me, give me "single box" players (external powersupplies are okay, external analogue stages are okay, just keep transport, DAC and clock on the same ring)....

Ciao T

 

I fully agree with you.

The problem is that people simply don't listen.. Instead the read crappola hifi mags that can be found at WH Smith, and are fed pretty much the same tripe by their dealers. This is why these rabid fantasies about cables manifest themselves - it has very little to do with people actually listening, and a hell of a lot to do with what they've read beforehand.

 

Forget all that....

Hook up with Issac as he has access to an Audio Precision box...

Then take whatever cable construction, length, etc you've "heard to work best" and take a set of measurements with that cable at the output of the dac.

The do the same thing with (a) the cable supplied by the CD/transport manfacturer (b) a radioshack cable.

Post both measurements here, compare and contrast the different measurements, and then use whatever material you can cite in the psychoacoustics literature to substantiate that the difference is audible.

You can skate around the jitter issue completely this way, as the only thing that really matters is the output of the DAC - a point that was made by Robert Adams (of Analog Devices) many years ago... [You've already read his AES papers no doubt..]

 

Hi,

Not very useful. I prefer looking at the actual signal in detail, rather than the decoded jitter residue.

Why would I want to measure a cable intended for digital transmission on the (analogue) output of the DAC?

Plus, the AP-One is not terribly usefull to analyse jitter, the Miller analyser is a much better choice, but out of budget.

I have read many papers that try to argue away the audibility of jitter, I am aware of DB listening tests that show that jitter can be audible, I am familiar with many papers that make jitter out to be the end it all.

As Solomon said in Ecclisastes - "To the writing of AES papers there is no end and too much devotion to them is wearisome to the flesh!".

Ciao T

 

Why not just use the decent set of analytical instraments provide free with that body.

As previously stated, if you can't hear the difference don't blame the cables. You may need to look elsewhere for the problems of low resolution within your system.

 

Looking is pointless because you are going to hear the decoded jitter residue...

Seriously, who cares what's going on in the digital interconnect - the question is, what comes out of the DAC (and ultimately the speakers).

The reason, I initially asked for the analog output at the DAC and not the speakers is because of the (comparatively) huge amount of distortion that speakers themsleves (and rooms) introduce.

I wasn't suggesting you analyse the jitter per se, just show it's audible effect in the output of the DAC.

The truth, again if you read Robert Adam's work - and hell he's on the design team at AD, so he should know, is that the Miller analyser too is useless.

Here we are discussing the jitter introduced by transmission through a cable assembly. Please site your references showing that this specifically is audible.

And where have you published your "research"? The Journal of Irreproducible Results perhaps....

 

oedipus,
you are the only one who's mentioned jitter - i suspect because it follows and bears out your preconceptions and prejudices when it comes to this subject however there are more factors at work than just jitter - one briefly touched on is impedence matching also the transmission of electrical noise from the transport to the dac via the i/c (hence some dacs manufacturers suggesting that optical connection is the way to go).
this is my problem with you objective types you think that your current understanding is all there is to know on the subject and your opinion is the only valid one - foolish imho, especially with a subject as 'subjective' as what makes good hi-fi.
i'll agree that the differences are small when compared to speaker / room interactions however if you have kit that is resolving enough it is possible to hear them.
as for being influenced by mags - which i don;t buy anymore btw - no, i've seen a member here correctly identify various different digital cables under truly blind circumstances - cables were changed by a sceptic and the guy was out of the room whilst changes were made. so your 'objective' comments don't match up with reality. sorry.
cheers


julian

 

Bzzt wrong. From Thorsten's earlier post... different cables can sound very different, simply because they make a large difference to the jitter levels.

Maybe you should read my earlier post which is where I predicted someone would take us down the jitter path...

Did you understand any of Thorsten's post???

They do that because it's an easy sales pitch to someone who know's nothing about optical transmission and has gross miscconeptions about electrical systems...

A man walks into a pub and claims either (a) he can juggle 7 balls (b) he can clear a snooker table (147 break) or (c) he can do a 9 dart finish. These are all documented as possible. Nevertheless, the other punters are intrigued and ask him to provide a demonstration of his ability. He politely declines. The reasons he gives are (a) the balls are the wrong shape for juggling (b) the on the snooker table is the wrong shade of green (c) the lighting at the dartboard is inadequate. Now the punters are skeptical and brand him a "bull shitter" - they know the task is theoretically possible, but our man is providing no evidence. The audience concludes that he simply can't do what he claims..

Now, when it comes to hifi, the man walking into the pub makes an extraordinary claim eg. "I can hear the differences between digital cables", but unlike the other three cases I state there simply isn't any evidence at all that this is possible.

If you (and your subjectivist bedfellows) want to advance "the current understanding" then demostrate your extra-ordinary abilities. As things stand, the facts are that no-one has heard Shakti Stones, or cables (there's a prize for that). And there's the old Quad test and Tom Nousianes ABX testing of amplifiers where nobody has discriminated between power amplifiers. Likewise for CD players.

The only thing people can tell the difference between is speakers. Even then people will fail to correctly identify 3dB, octave wide bumps in the frequency response - which is a GIGANTIC amount of distortion - compared to the wild claims that are made by people who baulk at the idea of testing.

Again, this is a misunderstanding. Not surprisingly, people with "good hearing" pretty much like the same thing. People with hearing deficiencies will tend to prefer speakers which act as a prosthesis for their impairment.

Ever play a game of chance? Do you know if the result was "statistically significant"?

Why didn't you participate? You claim you can tell the difference, so this would have been an ideal oppportunity to demonstrate your skill. Perhaps you're like the man walking into the pub...

 

oedipus,
i say potatoe you say orange - what do i care what you think - i know what i've seen and heard. can i 'prove it'? no. do i care? no. will i still offer advice to others based on my own experience rather than what i've read? yes. will you still counter with your own views? yes. is this what makes internet fora interesting? yes.
cheers


julian

 

Go Julian!

 

I am still interested to see on what basis you come about this 1-2m taboo length for a digital interconnect as I have not come across it yet. Further more is it based on theory only or have you actually heard faults with this length in used?

It is certainly interesting as I would guess that is what vast amount of people IC in used in real world.... so the implication would be almost everyone has been listening to crap so far. This is a big discovery if you are right.

 

when I bought my SilverBlue digital cable from AS, and was new to this game, I said that 1m was more than I needed - but I was encouraged just to loop it and expect no degredation. Typically the digital source and the dac are quite close, so going for 0.5m would generally be feasible - and if there are real sonic gains, then ...

 

I have heard earlier comments from manufacturers, among them Siltech and MIT, that claim 2 m is better then 1 m. Could also be because of the fact that they can then make more money off longer cables...

 

Signal travels at about 200 000 000 m/s, clock is about 3 000 000 Hz which implies a wavelength of about 66m. On the face of it theories regarding cable length and reflections don't seem likely.

But it would be best to use appropriate transmitter and receiver impedances with a matching cable and connectors. This is all available cheaply enough without recourse to audiophoolery.

Paul