Digital Audio Myths - Listening on a PC

oliverstoned wrote: and still, Jitter issue: "Jitter - the major enemy of CD playback Besides the limitation of CD's sampling frequency (which is becoming less and less an issue with improved filtering and replay methods which move the resulting artefacts outside the audible range) major sound degradation is caused by what the audio engineer calls 'timing jitter' or simply 'jitter'. Quite a while after CD was launched, people started to realize that even extremely small timing errors in the 'bits' coming from a CD and fed to a digital to analog converter were audible, making CD sound harsh and non-musical. Here one must recognize the difference between the digital information encountered in a Personal Computer and that of a CD; the two are often incorrectly compared. A computer is only interested in the sequence of zeros and ones. It does not matter at all whether these bits come very slowly, say via a 300baud modem or via an extremely rapid 100Mbaud Ethernet link. Irrespective of speed, the information will be the same; it simply may take longer to get it. " Thank you for providing this enlightening text ... it proves my point quite conclusively. I'm talking of audio extraction, not audio playback. When extracting audio, timing doesn't matter at all, and jitter is essently a timing problem. "The digital information on a CD, however, is extremely time sensitive. If the bits don't appear at the da converter at exactly the correct time it will generate sound elements which were not on the original recording. This in itself is easy to appreciate, but the accuracy of the timing is crucial and rather amazing. It is another demonstration of the human ears' ability. Digital audio extraction doesn't work in real time. The computer has all the time in the world to read the data correctly. Jitter doesn't exist in digital systems. ONLY when the digital data is converted to analog jitter can occur. I'm not arguing that bad computer sound cards create jitter ... but the Creative X-Fi beats many musical CD players in that regard. There are some musical CD players that are better, but the X-Fi is on par. I'll back that up with a link to the specifications of musical players and the X-Fi, if you're interested. So where could jitter come from (and my list will be far from comprehensive!): first of all lets assume that we have a CD player whose disc transport is so good that all information comes from the CD without any reading errors. Reading errors would mean some zeros or ones have been lost; some of them would be recoverable due to the error correction scheme (Reed-Solomon) stored with the original data. Reading error-free data from the disc is not easy; quite often the laser tracking system has to work very hard to keep the laser in focus. This in itself puts more of a burden on the power supply system due to continuous peak current demands. Data coming off the disk is timed by a in-built clock which in itself is often the cause for added timing errors. Whilst modern oscillators (which produce the timing baseline) are extremely precise, they are not perfect. And most importantly, almost all oscillators are extremely sensitive to vibration. So isolating the oscillator from the potential movement, both chassis mounted and air-borne is essential. However, the oscillator must be as close to the process as possible, but it is essential that its timing information is not affected by electrical noise, again either within the pcb or air-borne. Again, all of this applies to CD audio playback, not extraction.

“Again, all of this applies to CD audio playback, not extraction”

So you admit implicitly that a real drive reads better than a poor plastic drawer.

Here’s some more elements, related to computer issues.
Please read all before making comments.

Jitter on CD
From: Paul R [email protected]
My comments are:
Thank you for the best article on jitter I've ever seen anywhere.
Bob Katz's comprehensive treatment in enlighening.
He loses me on a few points, though, and I'd love it if someone could clarify.

First, I believe he states that Jitter is introduced in the conversion process, but is eliminated in the digital storage (hard disk, etc.). But then he speaks of jittery CDs. How is a CD different from other storage media? Why is jitter recorded on a CD?
Hello, Paul... Thanks. your comments are cogent. Apologies for the "work in progress". If we knew all the answers, we'd be geniuses! I will say that a large group of mastering engineers and critical listeners agree that CDs cut in different ways tend to sound different. The CD differs from other storage media in many ways, but the critical point is that the timing of the output clock and the speed of the spinning disc are related. The output of the CD player is a clocked interface, and the data are clocked off the CD disc in a "linear" fashion, one block of data after another. A buffer is used, which theoretically cleans up the timing to make it regular again. And for the most part, it does.
A lot of this is theory... no one has proved it as fact. And there may be more than one mechanism causing jitter taking place.
To obtain jitter in the low picosecond region requires extremely accurate timing. Any leakage current (interference) between the servo mechanism controlling the speed of the spinning disc and the crystal oscillator controlling the output of the buffer may unstabilize the crystal oscillator enough to add jitter to the clock signal. This does not change the data, by the way. If the servo is working harder to deal with a disc that has irregularly spaced pits or pits that are not clean, perhaps leakage from the servo power affects the crystal oscillator. It doesn't take much interference to alter a clock by a tiny amount.
This jitter is "ephemeral", though, because you can copy this data (irrelevant to the clock), and then play it back again from a more steady medium... and make it sound "good" again. This is not a permanent problem.
What makes the CD different from a hard disc, is the HD uses an asynchronous interface (SCSI or IDE). The disc is always spinning at the same high speed and the heads land on the spot you need when the data is requested. The data coming out is completely unclocked (it comes out in bursts) and has to pass through the SCSI barrier into a buffer located in a different chassis than the hard disc (the computer)... thus, there is great distance between the varying currents of the spinning disc motor and the oscillator driving the output of the buffer in the computer chassis. Since the computer chassis power supply only has to power the output oscillator, the result can be much more stable. Depends on how good the designer did his/her homework. Same for a CD Player... there are audiophile CD players where great attention has been made to power supply design, and these players exhibit much less jitter and better sound.
It is also possible to build a CD player based on a SCSI mechanism... possibly such a player would be more stable in playback than a standard CD player. You would have a computer in its own "cleaner" environment buffering the data. The Alesis Masterlink is such a player, and in another "chapter" of my work in progress I will have something to say about its audible performance.
I'd like to tackle a 200 page booklet to put all the pieces together someday, but haven't the time. I think in our FAQ there are some explanatory letters which help to cover the rough spots.
He also states that a 99th generation copy of CD is apparently identical to the original. But then talks about the degradation of making CDRs at 4x speed vs. 2x speed. Please help me reconcile this.
The data is identical... It's important to separate the message (the data) from the messenger (the clock).
It's all in the playback of the last disc in the chain, Paul! The "old" clock is NEVER transferred on each copy, only the data. No matter what speed you write at, there is a new writing master clock in the CD recorder that determines the spacing of the pits on the newly written CD.
But each time you copy, that clock is not transferred through the SCSI barrier of the next CD Recorder. I will have to write about this in more detail and diagram it for my readers, hopefully soon...
And each playback is anew... if the clock of the final playback is irregular, you will have jitter on the final playback of the last generation.
But you can clean that up yet again and start the whole cycle all over again.
I'm hoping the answers to these questions are within my grasp.
I think they will be, if I can just get the hang of explaining it properly!
Take care,
Bob

Toslink vs. Copper
From: Grant Lyman [email protected]
My comments are:
Bob, thanks for your informative web site and your great comments on the Mastering and Sonic newsgroups. I am hopeful I could get your opinion on a few questions I have. First, have you ever heard Toslink or Glass to sound as good as AES/EBU or SPDIF. My initial tests seem to indicate Toslink and even Glass tend to close the sound stage and thin out the sound. I have heard you mention in the past that the terminations on Toslink and Glass are critical for proper performance. Have you tested what you consider to be properly terminated Toslink or Glass against AES/EBU or SPDIF what was your conclusion.


I thank you, and value your opinion


Grant Lyman
Santa Barbara, CA
Dear Grant:
This is ultimately a jitter question, you know. My answer is that the apparent sonic differences between interface technologies such as Toslink, glass, and copper are IRRELEVANT when doing transfers or when passing signal from one processor to another. You can forget about that question with COMPLETE CONFIDENCE--since all of the technologies are capable of passing perfectly good data, within their specified cable lengths. Remember: the clock is not transferred along with the data. Only the data is transferred to the processor's circuits.
The apparent sonic differences between interface technologies come into play in only ONE place... and that is at the input to the converters (A/D and D/A).
If the D/A is susceptible to jitter on its digital inputs (as most are), then you will hear differences between toslink (plastic fiber), glass fiber, and copper (hard wire). Some D/As reject jitter better than others, and that will determine the extent you can hear these differences. REMEMBER: This is only important to that particular listening session (the D/A only) and not to any other circumstance.
In the case of an A/D, if placed on internal sync, then its jitter (and subsequent distortion) is totally determined by its internal clock ciruits. But if you have to lock an A/D converter with external "AES" sync, the interface technology chosen may affect the stability of the A/D. Locking an A/D with wordclock produces far less jitter because there is no audio on the wordclock line, it is a pure clock. Wordclock is the second-best way to lock an A/D short of using internal sync. In the case of AES/EBU, the audio and clock are on the same line, and the audio (and other data) can cause interference during the critical clock extraction process. The different technologies (toslink, glass, copper) have different bandwidths, and reduced bandwidth (as with plastic fiber) can cause greater interface jitter.
In any case, it is preferable to put the A/D on internal sync for the lowest distortion.
Only by placing the master clock of the entire system within the D/A converter and feeding all devices as slaves to that clock can we eliminate these "ephemeral" differences. That way the D/A is immune to clock-induced problems on its AES or SPDIF inputs.
How can we reconcile this issue of requiring the master clock be inside the DAC, yet the A/D has to be on internal sync for lowest distortion? You can only have one master clock in a system. The answer is to design an INTEGRATED A/D and D/A system where the master clock is on a buss, feeding all the critical internal jitter-sensitive elements with a low-jitter buss-interface.
That's what I've done recently in my system and I can attest that the "ephemeral" sonic differences have disappeared. (sigh of relief). At this time, I believe that integrated A/D/A systems with this technology can currently only be obtained from two vendors, TC Electronics (System 6000) and Prism. A consumer company called "Muse" has also adapted this technology on the consumer side, so there is hope. But it is sad and ironic that the audio industry has been so slow to adopt this technology, when the problem and solution have been known for years.
Hope this helps,
Bob

Hypotheses about jitter. A letter from magazine editor Greg Simmons, down under in Australia...
Greg discovered an apparent contradiction in my article on jitter: Why did I say that DATs don't seem to pick up jitter, but AES/EBU CDR's seem to pick up incoming jitter.
Date: Wed, 17 Jul 1996
Tp: Greg Simmons... Jodie Sharp [email protected]
Dear Greg:
Thanks for your comments. I'll see if I can clarify...please consider the article on jitter a work in progress. Your question did hit the nail on the head on some missing information in the article, and I thank you. In my copious (????) free time I'll try to clarify the article.
Dear Bob,
Your essays on dither and jitter are excellent, authoritive and very informative - I've learnt heaps from reading them. However, in your essay on jitter, you say some things that appear contradictory and have me slightly confused.
Firstly, you say that "...Playback from a DAT recorder usually sounds better than the recording, because there is less jitter. Remember, a DAT machine on playback puts out numbers from an internal RAM buffer memory,locked to its internal crystal clock." Shortly afterward, you say: "...a compact disc made from a DAT master usually sounds better than the DAT...because a CD usually plays back more stably than a DAT machine."
Under the heading 'Can Compact Discs Contain Jitter', you say "...An AES/EBU (standalone) CD recorder produces inferior-sounding CDs compared to a SCSI-based (computer) CD recorder. This is understandable when you realize that a SCSI-based recorder uses a crystal oscillator master clock." The text continues by discussing the differences between the PLL system used by a standalone AES/EBU recorder and the crystal oscillator system used by a SCSI recorder.
The paragraph closes with "...No matter how effective the recorder's PLL at removing incoming jitter, it can never be as effective as a well-designed crystal clock."
Do you see the source of my confusion? When discussing DAT and dubbing in general, the essay suggests that jitter on the incoming data is irrelevant during playback (so long as the jitter is not so high as to cause actual errors) because after being recorded, the data is re-clocked by the playback machine's internal crystal oscillatorlock. And yet, the essay also suggests that jitter on the incoming data (as in the case with the two different types of CD recorders) does affect the final sound.
Excellent point. I will have to include this answer in the next revision of the article:
First of all, the remnant playback jitter ("intrinsic jitter") of a DAT machine is significantly higher than the remnant jitter of a good CD transport. Bob Harley measured 1.2 nanosecond RMS jitter on the output of a Panasonic 3500! The remnant jitter on the output of a great CD transport is on the order of 10 to 100 picoseconds. A nanosecond is 1000 picoseconds, so you can see there is an order of magnitude difference.
Power supply design, grounding, can affect the quality of these cloks, and audiophile CD transport designers pay special attention to the power supply. A poor power supply can affect the remant jitter both by contaminating the crystal clock, and the AES/EBU trasmitter in the digital output stage. Until someone examines the internal mechanisms of both reproduction systems with very sophisticated measurement equipment, we can only hypothesize. But for now, it is enough to say that the measured intrinsic jitter of a DAT reproducer is greater than 100 times the jitter of a good CD transport. We all know that shouldn't be happening... all digital reproducers should measure perfectly--right? Good thing we are able to measure those differences, or the golden ears would all be in a pickle trying to demonstrate why DAT playback just doesn't sound as good as CD playback.
Now for your question, you recall that my tests with DAT recorders seem to confirm that jitter coming in is irrelevant to the final playback. This does seem to confirm the proper action of the phase locked loops and FIFO's in the DAT machine. But why doesn't it seem to hold true with CDRs? Well, the deeper we dig, the more we learn. On the surface, the science holds true, but...
One of my hypotheses is that the residual jitter level of 1200 picoseconds in a DAT reproducer has a very large masking effect. It is highly unlikely that any small remaining differences or variances (say plus or minus 100 picoseconds) due to variant jitter of sources could ever be heard or reliably measured. Especially after reduction through the recorder's input PLL, and especially after the separate blocks on tape are reassembled and then retimed through the reproducer's output FIFO. So the question with DAT machines becomes a moot point, as far as I'm concerned.
Another hypothesis is that the data block structure of the CDR is different from that of the DAT, and may have an effect on outgoing jitter. In both types of playback, however, data is extracted in a "jittery" manner, and always smoothed by FIFO, so the different data block structure would have to have an indirect influence on the output clock.
Another possibility is error correction, and again, only through an indirect influence, common impedance coupling through the power supply. Perhaps the CD player's design is more susceptible to that than the DAT.
It seems the problems I was alluding to are only relevant to a very low
jitter medium (such as CD). In a low-jitter CD player, we can examine and test for "microcosmic" influences on the stability of the player's crystal clock and see if they are caused by "microcosmic" differences on the CD disc. It took David Smith and Sony Corporation months and months to devise some sophisticated audio tests in order to conclude that the golden ears were right!
This brave work was undertaken by design engineers working for the very company that had designed the "perfect" FIFO system for CD players which is supposed to eliminate all outgoing jitter (or at least reduce it to the residual of a crystal oscillator). It will take months to years before scientists with sophisticated measuring instruments find and eliminate the subtle internal mechanisms in a CD player that are somehow permitting jitter differences to be heard through a supposedly "perfect" system. So far, no equipment designer has succeeded in producing a jitterless playback system (everyone says it's possible)--although great improvements have been made (listen to some of the newer audiophile digital reproduction systems and to a couple of the finest professional D/A converters).
We're trying to find flies on an elephant, here. Unfortunately, on the audio side of this mixed metaphor, the human ear can hear the flies very well.
A good scientist mustn't assume anything, nor take anything for granted, and must recognize that all conclusions are based on some underlying hypothesis or axiom.
Surely a CD player is just like a DAT machine on playback, and uses it's internal crystal oscillator to clock out the data, therefore reducing the problem to the jitter inherent in the internal crystal oscillator clock and eliminating any jitter caused by the disc recording process, whether the data was recieved via AES/EBU or SCSI. Or is there something I don't understand?
I've heard terms such as pit jitter and land jitter, are these whatyou're referring to?
Pit and land jitter on the CD may or may not be the cause of the differences we are hearing. Some other mechanism on the CD (size of pits, not necessarily the spacing of pits) may be causing the servo mechanism in the player to be more jittery. It is definitely not data errors. Research has shown that these CDs which we claim to sound different have identical data. But part of the problem may be due to error correction, with the error correction system causing problems, again by power supply coupling. Very far-fetched argument, yet to be proved. Same with the servo mechanism leaking into the power supply for the output crystal...engineers have found a 25 cent power-supply bypass capacitor in the digital section to do wonders on the audio quality, so this is pointing to the reasons.
And to complicate the matter, the analyzers which look at pit and land jitter on CDRs generally do not look at its frequency distribution. For example, 10 picoseconds of peak to peak jitter with a central peak at 3 Khz is likely more audible than 500 picoseconds of random (uncorrelated) RMS jitter.
It takes far more sophisticated equipment to make the second measurement. I've had a plant analyzer show the reverse result, RMS jitter was higher in the CD that played back with apparently lower jitter. That is, if pit and land jitter on the CDR is even the root cause of the sonic differences we are hearing. When we hear a CD that has a wider soundstage, greater apparent low level resolution, and other audible differences, we assume that is caused by jitter differences on the CDR itself. But this is only a very unscientific hypothesis. And no standards as yet have been developed that correlate measured jitter against listening differences.
However, advancements are being made, and a specialized test system that looks at the analog outputs of CD players (and D/A converters) has been developed.Paul Miller's company employs Julian Dunn's specialized test signal for this purpose.

Also remember that what I said in my article remains true: that you can copy from a CD that supposedly sounds "degraded" through a SCSI interface back to another CDR or to a hard drive, then cut another SCSI CDR, and the end result can sound better than the original if the new writer is better than the original writer! Jitter is NEVER transferred with the data to a new medium, if a clock is not involved. And SCSI does not involve a clock. Jitter is strictly an interface phenomenon, whenever a clock is involved.
Finally, I'm sorry to send you such a long winded message but I genuinely would like to understand these things. I suspect I may be interpreting your essay incorrectly. Please don't take this message as a criticism of your essay - I have nowhere near enough knowledge or experience in this field to criticise your essay!! I'm just confused...
No problem... Jitter is a complex subject, no one knows all the answers. I ask more questions than I have answers. Someday I will try to rewrite my essay to incorporate all of these considerations. I hope this letter helped!
BK

SCSI, IDE, & Jitter
From: Everett Comstock [email protected]
My comments are:
I hope you don't mind, but I am writing in hopes that you could help to answer a question for me. I recently finished reading Robert Harley's Complete Guide to High-End Audio, and I was wondering if there are jitter errors that take place within computer interfaces such as SCSI and IDE. I have read your article (which is excellent by the way!), and you seem to touch on the subject of computer based DSP cards, but what about the transfer within the computer? Can IDE or SCSI interfaces introduce jitter into the data stream, and if so, is it enough to affect the quality of the signal? Any info regarding this subject would be greatly appreciated.
Thank you,
Everett Comstock
Hi, Everett. Thanks for your comments. IDE and SCSI interfaces are unclocked interfaces which pass data asynchronously. As such, "jitter" is meaningless, because there is no clock! Data is passed completely irregularly over these interfaces and jitter at these interfaces is enormous. Sometimes it comes in bursts at 2 to 8 times speed, then there are periods of silence where there is nothing. It's a "pass me data on demand" type of interface.
Then, the data goes to a new storage device, and that's that. The data stored on the new storage device (the hard disc) has no jitter. That's right. Jitter is only a question when it is introduced during the playback when a clock comes into play again. And in the case of SCSI, the hard disc system doesn't operate in a clocked manner related to the digital audio rate at all, so even on playback, you get the same "burst" situation as in the first paragraph.
So, how does this affect your audio? Not at all. The date remains identical. It has been stripped of its clock and has no memory of how many "clocks" it has passed through during the hundreds of copies previous.
During the listening you may hear a difference between one or another hard disc-based system which is playing back identical data, you may appear to get differences when copying between such systems, but careful analysis of what is occurring will reveal that these audible differences are what I call "ephemeral", that is, manifested by the particular clocking that is occurring, and the stability of the clock. Each time you play back the data, that is when you may examine how it sounds. Even the situation I relate in my article about how different CDs sound different, while it is quite special, is also ephemeral, but "semi-permanent". What do I mean by that? Well, the CD player is a special case of a rotating medium where the rotational speed of the medium is intended to be related directly to the ultimate clock that is driving the final data. Thus, irregularities in the medium (the recorded CD or CDR) may affect the servo circuits in the player, which may then affect the power supplies driving the output buffer clock, which may then affect the sound during that particular playback.
Let's say that "poor-sounding" CDR was made on an inferior writer, or one writing at 2X to 4X speed. We seem to have some evidence that these differences are audible. So, what do you make of that? During the playback, at that time, if you transfer the output of that "poor-sounding" CDR back into your hard disc system and then cut once again at 1X speed on a better-quality writer, guess what! The end result is a better-sounding CDR. You've restored the quality that you thought you'd lost. That's what I mean by "ephemeral-semi-permanent"... The copy may even sound better than the "original".
Your precious data is safe, and ultimately you only have to worry about the ultimate playback. In fact, if you have a great D/A converter, one which is relatively immune from incoming jitter, you can play back that apparently "inferior" CDR and no even hear a difference. And you'll never know what hard disc(s) it passed through during the process.
Bob

And now, a good question from a DAW maillist. How can I justify using the term"sounds better" in the context of jitter, when in reality, it may just sound different! Furthermore: the best way to take care of jitter is within the D/A converter! There will always be jitter in every AES/EBU signal line, no matter what workstation, no matter what processor or recorder. And this jitter must be reduced (ideally--eliminated) within the D/A converter.
Subject: DEFINITIONS OF "better" versus "worse" sound
>>On Tue, 30 Apr 1996, Bob Katz wrote:
>> I have observed that I can copy a CD into the DAW, and make a new CD that sounds better than the original.
Steve Potter wrote:
>>Bob, how would you define 'sounds better'?
And I replied:
I've spent a lot of time studying this very topic! Including trying to quantify the results of listening tests. I feel that in many instances I am quite comfortable with using the term "better" as opposed to simply "different."
>>How can a listening test be objective? How can we separate "different" from "better"?
This is a very tough question to answer. For example, regarding listening tests for jitter, no one that I know has reached the point of being able to say: "100 picoseconds of white noise jitter mixed with 25 picoseconds of signal-correlated jitter sounds better than 100 picoseconds of signal-correlated jitter mixed with 25 picoseconds of white noise jitter".
No, we have not reached the degree of sophistication where we can judge "better" in that fashion.
However, a number of experienced listeners have been able to use the judgemental term "better" in ways that correlate quite well with the measurable physical phenomena that are under investigation.
For example:
First: one definition of "better" is the source which sounds closer to the analog master tape, or the live source if it is available.
Second: Those of us who have been chasing the jitter phenomenon have begun to educate our ears and recognize the sonic differences that different types and degrees of jitter cause. Please note that in every case I use the same D/A converter to monitor the different sources under test at repeatable monitoring gains.
If you wish to begin entering down this jittery road, I suggest you start listening to the easiest form of jitter to recognize, one which every user of Workstations can hear every day, while monitoring through a high-resolution playback system. (A high-resolution playback system consists of a good 20-bit D/A converter, wide range monitors in an acoustically treated room, power amplifier with wide dynamic range, and a quiet listening environment).
The easiest form of jitter to recognize is signal-correlated jitter. Signal-correlated jitter adds a high-frequency (intermodulation) edge to musical sounds when monitored on a susceptible D/A Converter. Obviously, a theoretically perfect D/A would not be susceptible to jitter. We must not blame the message directly...just that the message is contaminated with jitter.
Every day I load into the workstation connectors while listening through the desk, I hear (and am bothered by) the most primitive form of proof that correlated jitter is audible: The sound is different during the load-in than during the immediate playback from the hard disk! It also sounds demonstrably worse during the load in than during the playback.
This is attributable to the intermodulation of Sonic's master clock by signal-correlated jitter during the loadin. During playback, since the source is no longer feeding digital audio, even though the DAW is still locked to the external clock, the external clock is much more stable from the DAW's point of view. Its PLL is no longer modulated by the digital audio that is combined with the external clock. This well-known phenomenon, known as signal-correlated jitter, has been documented by researcher Malcolm Hawksford. See AES preprint titled "Is the AES/EBU S/PDIF Interface Flawed" AES Journal 1995. This form of jitter is quite audible.
After an engineer learns to to identify the sound of signal-correlated jitter, then you can move on to recognizing the more subtle forms of jitter and finally, can be more prepared to subjectively judge whether one source sounds better than another.
Here are some audible symptoms of jitter that allow us to determine that one source sounds "better" than another with a reasonable degree of scientific backing:
It is well known that jitter degrades stereo image, separation, depth, ambience, dynamic range.
Therefore, when during a listening comparison, comparing source A versus source B (and both have already been proved to be identical bitwise):
The source which exhibits greater stereo ambience and depth is the "better" one.
The source which exhibits more apparent dynamic range is the "better" one.
The source which is less edgy on the high end (most obvious sonic signature of signal correlated jitter) is the "better" one.
Does this help you?
>>Seems like this could be very subjective. I could almost certainly agree on 'sounds different.' To be fair, I have not been involved in the kind of research you have done in this area but I still feel there is alot of subjectivity involved.
>>I recently attended the NAB convention and watched some demos of video line doublers and quadruplers. While in some ways they 'improved' the projected image, I could not flatly say that they made every aspect of the picture 'better.' It was decidedly 'different' but among the group I was with we couldn't all agree on what aspects we liked and didn't like about the 'improved' picture.
>>Steve Potter | TV & Film Audio Post since 1987
>>V.P. Technical Operations
>>Larson Sound Center | (818) 845-4100 voice
>>Burbank, CA 91505 | (818) 845-2414 fax
That's for sure. Well, line doublers actually alter the data which is sent to the monitor, so, unlike with audio jitter reduction units, the data is changed, and you get into very valid subjective questions. The question of "better" is definitely a slippery subject. I don't pretend to have all the answers, but to me, the audio copy which sounds most like the original points the direction of the degradation. Then, I can relate an experience with two different jitter reduction units, both of which produced excellent-sounding outputs, but both sound very different from one another. One has a slightly "flabby" bass, the other a tighter bass. At least both of them sound "better" than the jittery copy as monitored without the jitter reduction. So, when comparing two different D/A converters or two different jitter reduction units, even more subjective judgment enters into the picture. I agree with Steve Potter that "Better" is a very complex subject! Here's a followup on the maillist from Peter Cook of the CBC:
Date: Wed, 1 May 1996
From: [email protected] (Peter G. Cook)
Subject: Re: DEFINITIONS OF "better" versus "worse" sound
A fine mini essay Bob. Perhaps you could add this on your web pages.
At 08:21 1/5/96, Bob Katz wrote:
Therefore, when during a listening comparison, comparing source A versus source B (and both have already been proved to be identical bitwise):
The source which exihibits greater stereo ambience and depth is the better one.
The source which exhibits more apparent dynamic range is the better one.
The source which is less edgy on the high end (most obvious sonic signature of signal correlated jitter) is the better one.
The better one, and it is better, is also easier to listen to. . . less fatiguing. I would also add to this that the low end just "feels" bigger nd more solid. This is perhaps a psychoacoustic affect more than a measurable one. It may be that the combination of a less edgy high end and greater depth and width makes the bass seem better.
All of this makes sense if thought of in terms of timing (that is what we're talking about isn't it ;-]). With minimal jitter nothing is smeared, a note and all its harmonics line up, the sound is more liquid (a term probably from the "audiophile" crowd but one which accurately describes the sound none the less), and images within the soundstage are clearly defined.
-Peter

Digital Patchbays, good or bad?
>Date: Fri, 30 Apr 1999
>From: kim [email protected]
> Ok I have been told that i can use a regular patchbay for my digtal equipment. I question the valitity of this request.(I'm talking about AES/EBU, Spidf). I would like to know if you have any thoughts on this.
> I guess theoreticly it should work but what I'm seeing out in the world are a lot of active digital patchbays. So I guess what I like to know is this, have any of you built and used just regular patch bays for digital audio interconnects. Now I'm looking at just using a adc patch bay with a punchblock on the backside.
> Will I have any signal disscrepencies ie ohm problems,
> the possiblity of blowing dacs ect...
> please comment
> thanks kim
Dear Kim:
You won't blow any DACs, but every impedance bump in the chain adds a degradation which will make your signal connections less reliable, and certainly add jitter, which adds distortion to the monitoring.
The punch block, even the XLR connectors (which are not truly 110 ohms), every point where one wire is connected to another...is a serious problem...these are all "impedance bumps". The jacks are also not true 110 ohm. You may find your wire length only good to a few feet before you get crackles, pops, or no signal at all.
I advise against using standard "analog" patchbays for digital, unless you convert to 75 ohm technology and use professional (video level) patch bays, or a certified impedance matched active patchbay. The same is true of XLR "patchbays" for AES/EBU. Every XLR plug in the middle degrades the integrity of the connection. XLRs were not designed to be digital connectors. This was perhaps the biggest mistake made by the AES. It helped us to get into digital audio in the beginning, but it's making lots of trouble now. I support the AES-3ID standard, which puts digital audio on 75 ohm coax with BNC connectors. Another valid technology is properly twisted pair CAT-5 cable, with RJ-45 connectors, running 10 base-T or 100-base T Ethernet. These can also be made with patchbays and cable runs that pass digital audio with high integrity.
I hope this helps!
Bob Katz

As you see, it's not that simple.

And Bob Katz is an obsolute reference in the digital domain.

He wrote the red book of digital mastering.

So he knows a bit -without play on word- on digital.

Wow, you two!

Still, a great thread!

Mike, I am learning so much from you!

MikeEnRegalia wrote: oliverstoned wrote: As you see, it's not that simple. And Bob Katz is an obsolute reference in the digital domain. He wrote the red book of digital mastering. So he knows a bit -without play on word- on digital. That's why he confirms my theory. Read closely ... with a topic like this, you'll have to pay attention to details.

May I point out some extracts:

The symptoms that I quote you are the same that the ones which are quoted there:


“It is well known that jitter degrades stereo image, separation, depth, ambience, dynamic range.
Therefore, when during a listening comparison, comparing source A versus source B (and both have already been proved to be identical bitwise):
The source which exhibits greater stereo ambience and depth is the "better" one.
The source which exhibits more apparent dynamic range is the "better" one.
The source which is less edgy on the high end (most obvious sonic signature of signal correlated jitter) is the "better" one.”

About alimentation (another issue):

“there are audiophile CD players where great attention has been made to power supply design, and these players exhibit much less jitter and better sound”


About clock problems :

“He also states that a 99th generation copy of CD is apparently identical to the original. But then talks about the degradation of making CDRs at 4x speed vs. 2x speed. Please help me reconcile this.
The data is identical... It's important to separate the message (the data) from the messenger (the clock).
It's all in the playback of the last disc in the chain, Paul! The "old" clock is NEVER transferred on each copy, only the data. No matter what speed you write at, there is a new writing master clock in the CD recorder that determines the spacing of the pits on the newly written CD.
But each time you copy, that clock is not transferred through the SCSI barrier of the next CD Recorder. I will have to write about this in more detail and diagram it for my readers, hopefully soon...
And each playback is anew... if the clock of the final playback is irregular, you will have jitter on the final playback of the last generation.”

About mechanic pb:

“To obtain jitter in the low picosecond region requires extremely accurate timing. Any leakage current (interference) between the servo mechanism controlling the speed of the spinning disc and the crystal oscillator controlling the output of the buffer may unstabilize the crystal oscillator enough to add jitter to the clock signal. This does not change the data, by the way. If the servo is working harder to deal with a disc that has irregularly spaced pits or pits that are not clean, perhaps leakage from the servo power affects the crystal oscillator. It doesn't take much interference to alter a clock by a tiny amount.”

MikeEnRegalia wrote:  Why are you throwing all this irrelevant stuff at me? 95% of it deals with completely different issues. I'm at work now, but I'll highlight at least 10 passages of these emails which confirm what I say - when I get around to it.

I'm at work too.

Up are the passages which confirms my views

Anyway, the more funny is that we agree on MOST points since the beggining.

I let you comment the passages i choosen.

cobb wrote: I believe this is what Mike is already doing. I think he posted earlier that his music is coming from hard drive- not cd [edit] this is in relation to goose's post 2 back

Exactly. I'm talking about ripping the music to the hard disk using lossless formats (WAV, WMA Lossless, Apple Lossless, FLAC) and then either playing it using either a digital connection to the amp, or a really good PC sound card like the Creative X-Fi or sound cards used for hard disk recording (studio equipment). 

Just looked up the specs the X-Fi. It looks perfect for the job.

cobb wrote: Just looked up the specs the X-Fi. It looks perfect for the job.

Agreed. And even if its D/A converter isn't good or seems too "cheap", one can always use the digital interface to connect it to a top-notch amp, and have the amp do the conversion.

I still think that the amp and speakers are the most important link in the chain.

Edited by MikeEnRegalia

cobb wrote: Correction- after looking at more reviews on this card, I would definitely be buying it. If I wasn't so attached to my trusty old DSP I would be ordering it myself. Very impressive card and not overly priced. 51 million transistors on board. Unheard of for a soundcard.

Actually, their sound enhancement feature called "Crystallizer" doesn't seem to be as good as the musical CD player algorithms. But the card is not yet available, and maybe further tests can clarify that.

BTW: I'll most surely buy this card ... even if that feature doesn't live up to the expectations, it still boost gaming performance and allows 128 simultaneous sounds instead of 64, and it simulates the audio filters in hardware instead of using the main cpu. I can't wait to play Battlefield 2 with this card ...