Will digital CD audio differ from player to player? (1 Viewer)

[Jun-Dai Bates]

John,

If S/PDIF is not framed or packetized, is it possible that it then does not contain any error correction? Also, if the clock is contained within the stream, why can't the DAC use the clock to retime the signal? Is this an intentionally bad design to market digital components and cables as superior to one another?

Also, is there another explanation for your ability to differentiate the transports? In fact, it seems likely that CD players are not just transports, even when using the digital output, because I bet the digital format that is sent over S/PDIF is different from the CD digital format.

 

[LanceJ]

You guys are doing the equivalent of being down on your hands and knees recording to the nano-meter the tread patterns on car tires trying to find out why the BMW drives so much better than the GEO Metro...

LJ

 

[AustinKW]

Chris,

Huh? Jitter is all there is. Tracking, pickup, accuracy and all the "other things going on" are trivial. The datastream is buffered so errors can be detected and either corrected or "better" data reacquired. Stability, heft, clamping mechanisms, isolators, etc., etc. All are useless - jitter is EVERYTHING. Solve the jitter problem and you solve the digital audio problem. $100 transports with PERFECT datastreams are quite doable. Only requirement is bidirectional control data. Once the protocol is widely adopted, Krell and Levinson are out of the player business.

Austin

 

[Craig_Kg]

Typos and grammatical errors abound, and his line of reasoning in that article is very poor.

Typos and grammatical errors do not alter the technical relevance of his statements and the capitals are being used to emphasize points (which is OK, IMO, although bolding would be better). Jun-Dai, in which portions of the article do you find the reasoning to be poor?

 

[Ian Montgomerie]

$100 transports with PERFECT datastreams are quite doable. Only requirement is bidirectional control data. Once the protocol is widely adopted, Krell and Levinson are out of the player business

High end audio parts are sold mostly on perceived quality, not real quality. I am entirely sure that even using technologies such as 1394 where the transport can be just a slave to the output component, you will still see super-expensive transports with thick metal cases, vibration dampers, lead weights, etc., etc.

I mean, this is a market in which people spend hundreds of dollars on digital cables. To my knowledge there are no tests consistently demonstrating that transport-induced jitter is audible in the ranges you normally find it in - but at least we know it exists as a phenomenon, audible or not. And for CD audio, some drives really will let a few more bit errors slip through than other drives, although again people greatly exaggerate the audibility of this. But any decent digital cable introduces neither jitter nor errors. The most expensive digital audio cable in the world doesn't transmit data any better, under household conditions, than a cheap coaxial video cable. This fact has not put manufacturers of expensive digital cables out of business, or stopped people from being extremely confident that they hear a clear difference between different digital cables.

 

[ChrisWiggles]

Actually, it is acting as a pure transport pretty much, the format used in S/PDIF if you're sending it from a cd player is PCM, which is what is used on the CD. It's picking it right off the disc then sending it along to the D/A converter.

 

[DaveLenhert]

Lee-

Good points, I will definitely do some reading of the material you listed and I would love to get my hands on one of your test CDs....definitely would be an interesting test to try.

Even though the human brain is an advanced neural network and a marval of "engineering". BUT, if it is observable (hear, see, etc) by humans, then you should be able to measure it. If you can't measure it, then you are measuring the wrong thing or the sensitivity of the instrument is not sufficient for the task.


Chris-

"You guys are doing the equivalent of being down on your hands and knees recording to the nano-meter the tread patterns on car tires trying to find out why the BMW drives so much better than the GEO Metro... "

, very true, we are debating that the writing on the Yugo speedometer is too small and neglecting that its a friggin' YUGO!

Being a classical music fan (and living in Philly), I naturally have season tickets to the Philadelphia Orchestra . It's really a blast to listen to recordings of the pieces that will be in that evening's performance and compare the interpretation of the pieces. Something else that is fun is to compare two recordings of the same piece. Both comparisons can show you the differences between, live vs recording, studio vs concert halls, mixing/re-mastering techniques, and others. Too bad that some of the best recordings are poorly recorded or poorly re-mastered to CD. It really gives you appreciation on how much "doctoring" is done on current, big name, $$$$ driven, popular music.

-Dave

 

[AustinKW]

Hi Chris,

Do a little research into CD fundamentals.

Pickup is trivial given buffering and error correction. Bit errors simply don't exist in modern CD players at just about ANY price. You don't have to track perfectly, you just have to keep the buffer filled with the right bits. That's how portables work - huge buffers, lots of initial tracking errors, lots of re-reads.

Again, I'll repeat it - jitter is EVERYTHING! Understand jitter, figure out how to minimize it and you've optimized the system. Clocking the DAC (whether onboard or remote) is where the action is right now. Solve the clock synch problem and you've solved the jitter problem. Solve the jitter problem and you've nailed the bitstream. Simple, huh?

Austin

 

[AustinKW]

Hi Ian,

I guess I was projecting a technical viewpoint onto the real world of marketing. Your points are VERY well taken.

I would note, however, that the lunatic fringe DOES have a legitimate point respecting jitter at this time.

The exact limits of jitter that effect audibility are of course in dispute. What is not in dispute is that the ubiquitous design of an input stream derived DAC clock provides a vulnerability to signal jitter.

When this particular bugaboo is technically addressed to the satisfaction of MOST a'philes, we can move on to the next "big issue" in audio - whatever THAT is.

I figure we'll have gone as far as we can when every audio argument centers on speaker cables, interconnects and the audible differences between digital coax and optical. We're ALMOST there but not quite!

Austin

 

[John Royster]

Austin,

Solve the clock synch problem and you've solved the jitter problem. Solve the jitter problem and you've nailed the bitstream. Simple, huh?

I couldn't agree more. As long as you have a perfectly clocked stream with some kind of reference clock from source to destination then you're golden.

And more to the topic of bit level errors. I could see a bit error in the least significant bits being very, very subtle...but errors none the less.

 

[Lee Scoggins]

is it possible that it then does not contain any error correction?

Jun-Dai,
Timing differences can be carried separately from error correction which is usually defined as making sure all the zeros and ones are exact replicas. I think your focus on the error correction is an entirely different issue.

 

[Lee Scoggins]

Clocking the DAC (whether onboard or remote) is where the action is right now. Solve the clock synch problem and you've solved the jitter problem. Solve the jitter problem and you've nailed the bitstream.

Agreed but with one big exception: disc replication has jitter!

This is very important. Just ask Telarc!

 

[Jagan Seshadri]

Lee said (a few posts ago)

We are recording engineers recording analog tape so there is no transport jitter to speak of and the ADC jitter is held the same.

Analog tape? The land of measurable wow-and-flutter? And we're concerned about picosecond jitter?

-JNS

 

[Lee Scoggins]

Analog tape? The land of measurable wow-and-flutter? And we're concerned about picosecond jitter?

Recording and playback are different things Jagan. There are ways to minimize wow and flutter in the recording stage but it is not avoidable for us since recording a live set is not convenient given our test setup.

On playback, the timing differences of jitter can be heard clearly on the 88.2khz hard drive.

 

[Lewis Besze]

If this were not the case, I would not be able to pick out 20ps and 200ps samples every time in listening tests.

Sorry don't buy it! You would fail badly on any reasonably conducted blind tests,but don't feel bad so is everybody else.

 

[Ian Montgomerie]

Agreed but with one big exception: disc replication has jitter!

See, this is why I don't respect your statements, Lee.

"Jitter" between the pits on the disc does not and cannot make any difference in the final output sound (except of course when it's used to encode a PSP key for SACD decryption, so without a certain jitter, you can't play the disc). ZERO DIFFERENCE.

You brought this up a few days ago and the technical details were explained to you. But it is like talking to a brick wall - you don't change your tune one bit even when you are shown to be totally wrong by people who know exactly how the technology works.

For those who weren't reading that thread, disc pit "jitter" has nothing whatsoever to do with the rate at which audio is output. All that could happen is, if it were incredibly bad (out of spec), the disc would be an unreadable coaster. As long as the disc is actually readable, the rate at which the transport sends out data is determined by its internal master clock. This clock is subject to jitter from the usual sources (such as power supply irregularity), but NOT from the details of what is on the disc. The drive master clock drives the process of reading the disc, not the other way around. What comes from the read head itself is an analog signal which is influenced by the pits on the disc. This signal is digitized, filtered, and error-corrected to recover the exact bitstream. That process takes place at a speed faster than 1X, with the extracted data feeding into an internal buffer. That leaves enough slack that if the occasional read error happens, the data can be re-read without changing the audio output rate.

 

[TimTurtino]

This is why science is having such a hard time in this country (this pretty much applies world-wide-- I'm not just being a chauvinst ). Everyone, but everyone believes that they can solve every problem if they take a good hard look at it and just apply some common sense and some good clean morals.

Your mind is an incredibly complex beast. That doesn't mean that it can leap tall buildings in a single bound. It does mean that it will go to incredible lengths to
A) Find differences
B) Assign those differences labels (i.e., the "top" CD player, or the "louder" one, or the "silver" one, or the "first" one, or the "nearer" one)
C) Repeatedly perceive the same differences.

Folks, if you've never taken a psychology or medicine class, then you really don't know how good the mind is at tricking itself into believing in differences. The vast majority of advertising, salesmanship, con artistry, etc. merely tries to distract the mind from correcting these errors.

This is not to say that no minute differences are perceptible, or that every audiophile is full of ****, but every now and then I'd really like to get some of these people in a dark room wearing a blindfold.

Let me just say for the record that I am not impressed that Lee knows what order he recorded the tracks on a disc he mastered himself.

Me

 

[KeithH]

So, I see that we all agree that the sound quality differs among transports. Glad to see that everyone understands this. :rolleyes

 

[Lee Scoggins]

See, this is why I don't respect your statements, Lee.

Ian,

I just don't understand why you think I am not getting it. I have given references from JVC, one of the leaders is disc replication, that specifically talks to jitter in the disc replication process, I have given links to articles on Bob Katz website where he discusses jitter in the glass mastering process...

I feel I have been as compelling as Colin Powell making the case...what else can I do?

The time code can include jitter RIGHT before the disc is manufactured. This is why XRCDs sound so good (in part), they minimize these jitter effects.

You simply have to be sure all jitter is minimized throughout the chain.

 

[Lee Scoggins]

Here is some more data for those interested in jitter and how it affects many areas of the chain (from www.digido.com and the mind of Bob Katz and others):

Attention CD Plants---a New Solution to the Jitter Problem from Sony: In response to pressure from its musical clients, and recognizing that jitter really is a problem, Sony Corporation has decided to improve on the quality of glass mastering. The result is a new system called (appropriately) The Ultimate Cutter. The system can be retrofitted to any CD plant's Glass Mastering system for approximately $100,000. The Ultimate Cutter contains 2 gigabytes of flash RAM, and a very stable clock. It is designed to eliminate the multiple interfering clocks and mechanical irregularities of traditional systems using 1630, Exabyte, or CD ROM sources. First the data is transferred to the cutter's RAM from the CD Master; then all interfering sources may be shut down, and a glass master cut with the stable clock directly from RAM. This system is currently under test, and I look forward to hearing the sonic results.

I hope this sheds further light.