[flecom]

Quote:

Originally Posted by hciman77 /img/forum/go_quote.gif In no properly controlled listening test has jitter at the level found in modest consumer CD players ever been shown to be audible by humans. I suggest you read Ashihara , Kiryu, Koizumi, Nishimura, Ohga, Sawaguchi and Yoshikawa "Detection threshold for distortions due to jitter on digital audio" (2005). They found jitter undetectable below 500ns. The lead Author and I corresponded for a while, he found one subject who "said" he could detect 150ns, however this subject was unable to replicate this in proctored tests. In practice nobody could detect jitter at 250ns so even the most cautious interpretatation is that jitter becomes audible somewhere between 250ns and 500ns. 25% could hear it at 500ns, 50% could hear it at 1 microsecond and all could hear it (to 75% reliability) at 2 microseconds. Even in the dismally poorly controlled Benjamin and Gannon (AES reprint) paper jitter was not detectable in music below 30ns, 10ns for a single pure 17k tone. Dunn's model and the model in the Essex paper are mathematical and never empirically tested they do not adequately account for masking, even Dunn admitted that his model was off in the light of Benjamin and Gannon's work. No commercial CD player has jitter levels anywhere near those found to be audible. The poster child for jitter in CD players is the Marantz 63/67 series. Even this fails to hit 700ps, this gives rise to jitter sidebands at -105db (worst case on an 11K pure sine wave signal on the analog out) , the jitter sidebands on the digital out are at -130db on an 11K sinewave. To hear jitter you can download jitter samples from Arny Kruger's web site, they start at -20db and decrease to -80db. If you can successfully detect even the -80db jitter vs unjittered signal you have excellent hearing, and this is jitter that is degrees of magnitude worse than even the poor old Marantz's analog out. Nobody is doubting the existence of jitter. I think its relevance to consumer products may be overstated somewhat by the high end audio community.

shhh!

i want to see if i can get somone to buy an $8000 frequency standard...

comeon, you guys know you want a GPS frequency standard for your CD player

 

[Mr_Sukebe]

Quote:

Originally Posted by hciman77 /img/forum/go_quote.gif Nobody is doubting the existence of jitter. I think its relevance to consumer products may be overstated somewhat by the high end audio community.

Bloody hell, I've been had!
There I was, believing that the mod had a genuinely positive effect, damn, must stop smoking the wrong things.
Guess I'd better get back to listen to some low bitrate MP3s, as the media also tell us that they're CD quality.

 

[rsaavedra]

Quote:

Originally Posted by hciman77 /img/forum/go_quote.gif No commercial CD player has jitter levels anywhere near those found to be audible.

This has been my intuition since I learned about jitter some years ago. Despite the existence of jitter, I´ve always thought the true perceivable differences between digital sources (whether separate trasport+DAC vs. integrated CD or SACD or DVDA players) are mostly due to differences in the DAC and in the output stages, not in jitter specs.

 

[hciman77]

Quote:

Originally Posted by Mr_Sukebe /img/forum/go_quote.gif Bloody hell, I've been had! There I was, believing that the mod had a genuinely positive effect, damn, must stop smoking the wrong things. Guess I'd better get back to listen to some low bitrate MP3s, as the media also tell us that they're CD quality.

I am genuinely sorry for your loss. If it is any compensation I have also spent money on imaginary upgrades in the past so please dont feel too bad about it. There are self-help groups out there I think and its only money so it is no big deal.

I think you conflate a few things here, hence your humorous tone and irrelevant references to Mp3. Incidentally I dont dispute that some people can tell the difference between even high bit-rate MP3 and uncompressed audio, we have blind tests that show that to be so. Blind tests are great as they remove oh so many human biases, but I digress.

I am quite prepared to believe that a mod can make an audible difference, if it can be shown in properly controlled blind tests of course and I would even give credence to the audible effects of jitter reduction under the same circumstances. To some extent I trust what I can hear, but I am also aware that human perception while very sensitive in some respects is very unreliable in others, perceptual memory being a key one. The curse of having multiple degrees in psychology.

I dont dispute that component changes may change things audibly or that different components can sound different, blind tests can be summoned up to show this, non anecdotal proof is always nice, I am skeptical though about jitter being a problem since nobody has shown to my satisfaction that it is in fact a problem in modern components.

If jitter at the ps (10 ^ -12 seconds) level is audible then no modern TT would even be listenable due to the speed variations that are vastly inferior - 0.2% not being uncommon.

 

[Pars]

I think that people make the mistake of equating jitter in the digital domain with wow and flutter on a turntable, which I don't believe is an appropriate analogy. SInce I spent much less building my Tent/flea/PSU combo than most "affordable" interconnects touted around here (<$80), I'll trust my ears. Discrete output stage next...

BTW, something I hadn't seen mentioned but brought to light by rsaavedra is DACs... the current delta-sigma DACs are basically a cost cutting measure by the chip vendors... too time consuming and costly to match/trim the resistors on an R2R DAC, hence the delta-sigma chips.

I need to read the references posted by hciman77, but here's another reference for you (which I also have not yet read).

http://www.iet.ntnu.no/courses/fe811...t_audiodac.pdf

and

http://www.jitter.de/pdfextern/jitter92.pdf

These came from this thread on diyhifi.

 

[hciman77]

Quote:

Originally Posted by Pars /img/forum/go_quote.gif I need to read the references posted by hciman77, but here's another reference for you (which I also have not yet read). http://www.iet.ntnu.no/courses/fe811...t_audiodac.pdf and http://www.jitter.de/pdfextern/jitter92.pdf These came from this thread on diyhifi.

I know these references. The first quotes Dunn and the second is Dunn.

The first specifies the resolution degradation of jitter and the second models the audibility of jitter. In their graphs they show the effect of 5ns 1k jitter on a 16K signal - it shows sidebands at the -85db level.

If you want to see what 60hz jitter looks like ...

http://www.pcabx.com/technical/jitter_power/

The question is how audible is this degradation. It seems as if random jitter is much less of a problem than deterministic jitter, the Ashihara paper used random jitter which has the effect of raising the noise floor so the effect is broad across the whole spectrum.

Deterministic jitter has more focussed effects, this may explain why the Benjamin and Gannon thresholds are so much lower. Also B & G used jitter frequencies between 1500 and 1900 that cause the most detectable distortions. Nevertheless even here 30ns was required for audible distortion, according to Nishimura and Koizuma jitter tests of various DA systems have failed to ever find any with jitter levels above 3ns.

 

[PhilS]

Quote:

Originally Posted by hciman77 /img/forum/go_quote.gif I am genuinely sorry for your loss. If it is any compensation I have also spent money on imaginary upgrades in the past so please dont feel too bad about it. There are self-help groups out there I think and its only money so it is no big deal. I think you conflate a few things here, hence your humorous tone and irrelevant references to Mp3. Incidentally I dont dispute that some people can tell the difference between even high bit-rate MP3 and uncompressed audio, we have blind tests that show that to be so. Blind tests are great as they remove oh so many human biases, but I digress. I am quite prepared to believe that a mod can make an audible difference, if it can be shown in properly controlled blind tests of course and I would even give credence to the audible effects of jitter reduction under the same circumstances. To some extent I trust what I can hear, but I am also aware that human perception while very sensitive in some respects is very unreliable in others, perceptual memory being a key one. The curse of having multiple degrees in psychology. I dont dispute that component changes may change things audibly or that different components can sound different, blind tests can be summoned up to show this, non anecdotal proof is always nice, I am skeptical though about jitter being a problem since nobody has shown to my satisfaction that it is in fact a problem in modern components. If jitter at the ps (10 ^ -12 seconds) level is audible then no modern TT would even be listenable due to the speed variations that are vastly inferior - 0.2% not being uncommon.

Some of your posts in the past few weeks suggest you are becoming more dogmatic on the value of blind tests --or maybe I'm just reading them that way.

I agree that they are probative, but I hardly think they are conclusive. Or to put it another way, the absence of a blind test supporting an alleged audible difference does not mean the difference does not exist, or that the difference should be doubted until confirmed by a test. Furthermore, even a failure of a blind test to "prove" a difference does not mean there is no difference. Blind tests are not perfect, i.e., that they have flaws just like other tests. And the fact that some blind tests show that people can hear the difference between high bit-rate MP3 and uncompressed audio doesn't mean that the test is infallible in all situations and, therefore, that any failure of a blind test to find differences in other situations is conclusive.

All of this is probably obvious and you may even agree with some of it or a lot of it, but I thought I would point it out anyway, as there does seem to be a lot of posting lately by you and others suggesting that blind tests are the be all and end all.

 

[meat01]

Hi Phil, do you have another method that determines if a $300 upgrade is really worth it or not? I understand where hciman77 is coming from. Right now, a blind test seems to be the best way to take placebo out of the equation, since it is a strong factor. My argument has always been that if the change is worth it, then it should be apparent even with a blind test. The problem is that blind tests are not always an option.

 

[robert]

Quote:

Originally Posted by Pars /img/forum/go_quote.gif BTW, something I hadn't seen mentioned but brought to light by rsaavedra is DACs... the current delta-sigma DACs are basically a cost cutting measure by the chip vendors... too time consuming and costly to match/trim the resistors on an R2R DAC, hence the delta-sigma chips.

In conclusion, I should keep my Adcom GDA-600??? Current CDP/DACs at reasonable cost not being of any better specification?

 

[Pars]

Quote:

Originally Posted by robert /img/forum/go_quote.gif In conclusion, I should keep my Adcom GDA-600??? Current CDP/DACs at reasonable cost not being of any better specification?

I don't know... do you like it? There is an awful lot you can do to a good CDP via output stage (discrete), clocking, and improving the power supplies, but you really need to analyze the players strengths and weeknesses to make valid judgements. In general, although external DACs seem sexy, a one box CDP if properly implemented will beat a transport/DAC combination hands down (or should). My brother owns a '90 vintage Adcom (not sure if it is the same model as yours), and still likes it.

Can you replace your Adcom with something substantial and well regarded for a reasonable price? Its always a point of diminishing returns that you need to weigh... how much will it cost me to do upgrades vs. resale value (will I get any return on that investment) vs. cost of new (and hopefully better) deck. I took the chance with my Rotel RCD-855 that putting $70-$80 into a clock upgrade was worth it. I would not have bought a $300 upgrade for it (Audiocom, etc.). And I also think that the Tentlabs stuff is the best out there (or at least one of the top 3).

My comment was based on a thread on diyhifi.org regarding the possibility of building your own DAC "chip" from commonly available FPGAs coupled with discrete resistors if you want (no one has done anything... yet). Sounded intriguing to me. Someone (can't remember who) had commented regarding the reason for the demise of R2R DACs. The TDA1541(a), which was an '80s R2R DAC, is still held in high esteem by many. The PCM1694 (IIRC) is current (IIRC, again) and seems to also be well thought of. Many of the regulars over there are very experienced digital designers (Jocko Homo, Jim Hagerman, John Westlake posts some, Gordon Rankin, etc.), so until I know better, I trust their opinions. (Jocko btw thinks that jitter to 2ps is audible...

). Within reason, low jitter is certainly worth pursuing to the extent possible, irregardless of what any published papers claim for audibility. Its when you take things to an extreme that you start on the downside of the 90/10 rule (or 80.20, whatever).

BTW Flecom, maybe I should see if I could "borrow" a Stratum 1 clock from work and get that to work?

 

[lowmagnet]

How would a new clock inside a source help any if the receiving end of the pair has the dual disadvantage of an unshared clock and possible interface jitter? I'm just thinking $300 would be better spent elsewhere.

 

[morphsci]

Quote:

Originally Posted by lowmagnet /img/forum/go_quote.gif How would a new clock inside a source help any if the receiving end of the pair has the dual disadvantage of an unshared clock and possible interface jitter? I'm just thinking $300 would be better spent elsewhere.

I think you may be confused, the new clock is for the DAC (either separate or within a one-box unit), after the DAC the signal is analog.

 

[lini]

Quote:

Originally Posted by rsaavedra /img/forum/go_quote.gif This has been my intuition since I learned about jitter some years ago. Despite the existence of jitter, I´ve always thought the true perceivable differences between digital sources (whether separate trasport+DAC vs. integrated CD or SACD or DVDA players) are mostly due to differences in the DAC and in the output stages, not in jitter specs.

Do you have some good modder workshop around? Chances are that you could hear two otherwise identical players with and without clock upgrade there.

For myself, I've quite frequently been visiting Gerald Gessner, a former loudspeaker builder who's specialised in cdp modding (especially Marantz players) nowadays, back then when he still had his workshop in the centre of Munich (late 80s/early 90s). At that time he still mainly built speakers, but already dug into cdp modding - hence I often had the chance to compare different modding stages: To my ears, turntables had something to their sound (mainly in terms of imaging/palpability and rendering of highs) which cd players simply couldn't reproduce - until I could finally hear and compare a clock-modded unit.

As already hinted to some answers above, I don't think clock modding is worthwhile for every player, though. If it's already around or blow 150 ps stock, I'd rather first look into power supply, output stage, rcs terminals, chassis damping, feet...

Greetings from Munich!

Manfred / lini

 

[rsaavedra]

Quote:

Originally Posted by lini /img/forum/go_quote.gif Do you have some good modder workshop around? Chances are that you could hear two otherwise identical players with and without clock upgrade there.

No, not here. While I lived in the US I got my Sony NS500 player modded with the Superclock by SACDmods. However, iirc the mods also included some black gate output capacitor replacements in the output stage. I could not listen to non-modded vs. modded instantaneously, just non-modded, then weeks later the modded one. A friend of mine had a stock NS500 by then, but we never compared them side by side. Then later on I sold that Sony once I modded my Toshiba 3950. The Toshiba mods did not include replacement of the stock clock, but power supply, opamps (OPA627), and many capacitors on the audio board (the whole Vinnie Rossi mods). Eventually I liked the sound from the Toshiba better than from the Sony -that's why I sold the Sony.

 

[lowmagnet]

Quote:

Originally Posted by morphsci /img/forum/go_quote.gif I think you may be confused, the new clock is for the DAC (either separate or within a one-box unit), after the DAC the signal is analog.

Ah, so you're talking about re-clock the internal CD player DAC and using its line-out or headphone out, right?