Digital signal cables and "bits is bits"

[Griffinator]

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On 7/11/2003 2:50:53 AM mac_daddy wrote:

how about this..?

http://www.crutchfield.com/cgi-bin/S-kPQg5moZcpo/prodview.asp?i=119SV1i11H&s=0&cc=01

$20 for 1.5 m is a fair price, correct?

This should be good enough for the DAT transfer, right?

thanks again for all the advice.

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No - that's a composite video cable. Monster doesn't build their analog video and audio cables to the same tolerance specs they do their digital coax (for a very good reason - it's not necessary with analog signals)

http://www.crutchfield.com/cgi-bin/S-k1B8q7SW1dC/ProdView.asp?s=0&c=9&g=37500&I=119IDL1M&o=m&a=0&cc=01&avf=N

http://www.crutchfield.com/cgi-bin/S-k1B8q7SW1dC/ProdView.asp?s=0&c=9&g=37500&I=119IDL2M&o=m&a=0&cc=01&avf=N

Those are your digital coax cables.

[Griffinator]

Hey Randy.

Just curious - did Belden give you a breakdown of that cable's construction? I'm interested to see it.

[Stephen328]

Now the next time a Best Buy employee tries to tell me that all CD players sound the same i can drag out my diatribe for even longer. At least 2 hours. Actually I did find this thread quite interesting. Makes me want to buy an SACD player, or an Record player. Prehaps I should keep typing for severeral hundered more lines just to maintain the status quo. On second thought, maybe I won't.

[mac_daddy]

this one:

http://www.circuitcity.com/detail.jsp?c=1&b=g&qp=00401&bookmark=bookmark_20&oid=8407&catoid=-8748

thanks again.

[Randy Bey]

As I remember it: foamed teflon insulation, 18 gauge bare copper solid conductor, aluminum tape and shield, polyethylene jacket.

I added a second aluminum shield with a .01uF cap.

[Deang]

This thread is absolutely maddening. How you guys mananged to stay with it is beyond me. It's enough to prompt me to buy a turntable -- and I am NOT kidding.

My understanding has always been that jitter is the biggest problem in systems utilizing separate transport and DAC.

[Marvel]

I don't get the jitters too often, but I am feeling a little shaky right now!

Marvel

[toddc]

My apologies for disappearing for a couple days. Life got in the way and I received a new (vintage) tube amp from NOS Valves. But it appears the posts got much shorter as a side benefit of me going away.

Okay, time for me to admit that jitter has the theoretical potential for more than absolutely zero affect. But aside from theoretical it is effectively zero.

I searched on JAES and Jitter.

Here's a succinct summary from one:

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Although rarely observed in a well designed player, jitter is a worthy topic of discussion because of both its misconceptions and the large amount of press it has received. Jitter is basically defined as time instability. It occurs in both analog-to-digital and digital-to-analog conversion. The latter instance is the only concern here. Jitter occurs in the compact disc player when samples are being read off the disc. These reads are controlled by the pulses of a crystal oscillator. If the system clock pulse inaccurately (an unlikely event), if there is a glitch in the digital hardware, or if there is noise on a signal control line, the actual reading time will vary from sample to sample thus inducing noise and distortion in the extreme case.

A great deal of money has been made by shrewd marketeers preying on the fears of the consumer worried about jitter. Such products marketed include disc stabilizer rings to reduce rotational variations, highly damped rubber feet for the players, and other snake oil remedies. However, the careful engineer has beaten the marketeer to the punch by having the samples read off the disc into a RAM buffer. As the buffer becomes full, a local crystal oscillator can then "clock-out" the samples in a reliable manner, independent of the transport and reading mechanisms. This process is referred to as timebase correction and as stated before, any quality piece of equipment will implement it.

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http://www.tc.umn.edu/~erick205/Papers/paper.html#jitter

Note that when he said "well designed" player he wasn't referring to high-end audiophile equipment, but rather "any quality piece of equipment"

And from another site...

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Does is matter whether I use optical or coaxial digital input when recording to Minidisc? Is jitter a problem?

In a word: No. The perceived problems with optical interconnects relate to an optical cable's greater theoretical potential to distort the digital signal, particularly to create small inaccuracies in the arrival time of data bits ("jitter"). However, in Minidisc recording jitter is not an issue since the digital input signal's sample values are recovered and passed directly into a memory buffer or into a sampling rate converter that is clocked with the clock embedded in the input signal. The sampling rate converter and/or memory buffer allow the audio samples to be subsequently read and passed to the ATRAC converter with an accuracy determined by the MD unit's internal quartz clock. Even if jitter was an issue however, it is doubtful that the short cable lengths involved in home HiFi systems could produce audible differences between optical and digital cables.

Regarding the occurrence of outright bit errors due to a marginal cable: S/PDIF contains only parity information, there is no error correction capability. If the errors are bad enough to cause bits to arrive with incorrect values, the likely result is that the digital audio receiver will not be able to lock on to the signal.

A short paper by DJ Greaves goes into further detail about S/PDIF, and has some comments about why jitter is not a problem even in equipment without buffers. Another paper by Tomi Engdahl goes into great detail about S/PDIF, even giving schematics for AES/EBU <-> S/PDIF conversion. Finally, Digital Domain has written a very comprehensive paper on jitter in digital audio systems.

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http://www.minidisc.org/faq_sec_4.html#_q34

Note that they refer to this as a "theoretical potential". That is the key point. We could stop there and go home. They continue however with a few additional points:

First, it is doubtful it could produce an audible difference in home HiFi cable lenghts.

Second, if errors did occur it would be unlikely that the signal could be decoded. In other words, you won't hear the highs rolled off you'll hear a skip.

Third, they have guarded agaist any potential impact by using a buffer and clock on the receiving end (as I discussed in an earlier post). As one of the referenced links then goes on to say:

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Even modern DACs have typically a small buffer and reclocking circuitry, so the jitter is not so big problem nowadays that it used to be.

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So then the answer is not more expensive cables (*IF* you even believe jitter could theoretically have an effect on sound that is audible). It is to make sure you have a relatively current player that is not poorly designed by standard market definitions (not by extreme audiophile definitions). In other words, most any major manufacturer's player made in the last 5 years (10?).

This makes sense. An engineer designing a component (say the DAC) would be able to see the bits coming in. If he was able to measure any data anomalies that flipped bits (corrupted words) then he would implement one of the solutions above. Actually, he'd implement them anyway since that's how you handle digital information regardless. That's how any engineer would solve it at any major electronics company. He wouldn't go out and buy monster cable and tell his boss his ears found the solution.

My bottom line is this: if we can make a $3 cat-5 cable that works great for digital in the computer world where big dollars count on reliability, why would Audio need a $50 cable, or a $200 cable to send a digital signal.

Please don't answer that. It's a rhetorical question and as said above by the professor there are plenty of great marketers who can spin up a great answer.

However, if one still believes that jitter could possibly have an audible affect in their system then they should perform a simple double-blind test to demonstrate it and find a solution. Use three different cables and have some friends help you keep the test blind. Be sure and have some good wine, dinner and music selections on hand during the test; otherwise the evening will be a complete waste.

I stick by my original point that everything prior to the DAC is basically irrelevant. Bits is bits. If your DAC is outboard or in your receiver then get a cheaper player, a cheap cable, and spend more money on discs.

Cheers