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j..i...tter-Pod?

post #1 of 17
Thread Starter 
I'm relatively new to this forum, and I’m definitely not an electrical engineer, so I wanted to see if any of you could shed some light on an issue I’ve been contemplating for a while now.

After skimming through a really interesting article (http://www.tnt-audio.com/clinica/jitter1_e.html), I was curious to see if any of you had opinions about the effects of jitter, if anyone can really hear them, on computer-related music.

I imagine that something like an iPod nano would introduce relatively little mechanical jitter of its own, since it isn't spinning a disc, but what about all of the interference added to the data as it was being ripped from the CD at high speed to a hard drive and then transferred from a noisy computer to the iPod? It seems like high end equipment manufacturers place a huge emphasis on transport stability, tracking accuracy, and interference reduction. Do you think that these characteristics, which are pretty much forfeit on computers, impact the sound much, and are there options for getting a more accurate signal into a computer or an iPod?
post #2 of 17
The only reference to ipod jitter is the stereophile review. JA measured it at 225 ps I believe, which is pretty good.

EDIT: http://www.stereophile.com/mediaservers/934/index5.html

2nd EDIT: I actually have been thinking about this for awhile. You would think since the info is buffered from the hardrive and sent to the DAC, there would be virtually no jitter. Unfortunately, that is not the case. Jitter are essentially timing errors. The info from the drive is sent through I2S to the DAC, which could possibly be one source of kitter. Another is the 64 mb or so of SDRAM that is used as a buffer to load and sync the info, couldn't tell you how in depth the filter is but that could also be another source for jitter. But at the end of the day your only at 225 picoseconds which ain't too shabby.
post #3 of 17
Quote:
Originally Posted by mark6.190059 View Post

I imagine that something like an iPod nano would introduce relatively little mechanical jitter of its own, since it isn't spinning a disc, but what about all of the interference added to the data as it was being ripped from the CD at high speed to a hard drive and then transferred from a noisy computer to the iPod? It seems like high end equipment manufacturers place a huge emphasis on transport stability, tracking accuracy, and interference reduction. Do you think that these characteristics, which are pretty much forfeit on computers, impact the sound much, and are there options for getting a more accurate signal into a computer or an iPod?
Jitter at the level found in commercial audio products has never been shown to be audible, to make jitter audible the Stereophile test CD uses a 20ns jitter on a 11K or 17K signal , both regions of very high jitter susceptibility, no commercial product ever tested anywhere has had measured jitter of greater than 4ns, that being the Oppo 970HD, whatever issues of sound quality may exist jitter is unlikely to be a source of grief. The Benjamin and Gannon paper found subjects could detect jitter of 10ns on a single high frequency pure sine wave, in music it was 20ns, masking takes care of adjacent sideband signals that are a mere 35db down , with jitter you are normally looking at between -85 and - 130db sidebands, the Ashihara paper set the threshold at 250ns but they used random jitter which has a diffuse effect raising the noise floor and lowering the effective resolution. For all intents and purposes jitter just isnt a problem in commercial audio kit.
post #4 of 17
Quote:
Originally Posted by hciman77 View Post
Jitter at the level found in commercial audio products has never been shown to be audible, ... For all intents and purposes jitter just isnt a problem in commercial audio kit.
Amen!
post #5 of 17
Thread Starter 
Wow. Thanks for the thoughtful replies and the excellent link. One thing that wasn’t clear to me in the review was if the diagnostic test signal for jitter originally came from a computer program or if it came from a CD that was ripped onto the computer. In the former case, it seems like the 225 picoseconds figure would only reflect jitter introduced post hard drive possessing and not to jitter potentially introduced during the CD information transfer.

In either case, it doesn’t sound like it should be something that I’ll ever perceive, but I was kind of curious because I have heard supposed reports of jitter related to high speed CD-to-CD coping via computers.
post #6 of 17
Thread Starter 
Quote:
Originally Posted by mark6.190059 View Post
One thing that wasn’t clear to me in the review was if the diagnostic test signal for jitter originally came from a computer program or if it came from a CD that was ripped onto the computer.
OK...I must be on drugs b/c the computer program would have to come from a CD or the internet anyway. Maybe the 225 figure represents the cumulative effect of all these processes, which would be great, and I should just stop analyzing this before I give myself the jitters.
post #7 of 17
Quote:
Originally Posted by mark6.190059 View Post
OK...I must be on drugs b/c the computer program would have to come from a CD or the internet anyway. Maybe the 225 figure represents the cumulative effect of all these processes, which would be great, and I should just stop analyzing this before I give myself the jitters.
I concur
post #8 of 17
Quote:
Originally Posted by mark6.190059 View Post
I should just stop analyzing this before I give myself the jitters.

Very funny! It could be said that the over-analysis jitters is more of a threat to the enjoyment of music than digital jitter.
post #9 of 17
Quote:
Originally Posted by islewind View Post
Very funny! It could be said that the over-analysis jitters is more of a threat to the enjoyment of music than digital jitter.
Good one! That actually has signature potential..I'll think about it
post #10 of 17
Thread Starter 
Less than 24 hours from curiosity and concern to conclusion and contentment…not a bad turnover rate at all. All thanks to Head-fi and the Headphoneus Supremi.
post #11 of 17
Quote:
Originally Posted by recstar24 View Post
Good one! That actually has signature potential..I'll think about it
Seriously, that would be quite an honor if you chose to use it. I definitely admire your "stop upgrading, buy music now" credo.
post #12 of 17
Quote:
Originally Posted by hciman77 View Post
Jitter at the level found in commercial audio products has never been shown to be audible... For all intents and purposes jitter just isnt a problem in commercial audio kit.
"Problem" correct, No. But Jitter most definitely has an impact on the sound of every single piece of digital hifi gear any of us has heard. It is part and parcel of what gives a souce it's particular sound signature. Heck, jitter is introduced in the D-A converstion (more so in some designs than others).

But correct, it should never be audible in terms of "oh There! THAT was jitter... and now... and now again! wow this is bad jitter" - this simply doesn't happen.
post #13 of 17
Probably the highest contribution to jitter in the iPod is the master clock oscillator. This is a quartz crystal based oscillator. Next to that, the logic and switching-induced noise will introduce some jitter as well. The sound of it depends on both the spectra and magnitude.

I dont know if the most objectionable thing is the jitter in the iPod or the D/A and op-amps, but it isn't perfect or as good as it could be IMO.

This is why I'm planning to mod a digital I2S interface on my iPod.

Steve N.
post #14 of 17
Jitter is a hoodoo designed to sell high end audio equipment.

See ya
Steve
post #15 of 17
hoodooyoudo? :P
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