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Jitter question...

Discussion in 'Recording' started by Bri, Aug 12, 2003.

  1. Bri

    Bri Active Member

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    Cincinnati
    I was made aware of "jitter" a while back, and was curious if anyone could tell me how my setup faired in regards to jitter, and also if there's an advantage to using something like Apogee's Big Ben.

    Currently I'm going out of my mic pre's, into an Apogee Rosetta 96k, then out the spdif of the Rosetta and into the spdif input of a Digital Audio Labs CardDeluxe, then recording into Sonar at 24bit 96khz, then back out the CardDeluxe through its balanced analog outs, into a mackie 1402VLZ, then to my monitors.

    Is there a weak spot here in regards to jitter? Aside from that, can the Rosetta's inherent jitter be improved using a clock source such as the Big Ben, and would there be a noticeable difference?

    I was also contemplating purchasing a Benchmark DAC-1 and just going out of the CardDeluxe spdif to the Benchmark, then to the monitors. Would this be significantly better than my current setup?

    I would appreciate your advice

    Thanks --Bri
     
  2. Opus2000

    Opus2000 Distinguished Member

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    Apr 7, 2001
    Hi

    First off let me introduce myself..I am Opus..moderator of the DAW world section as well as the Apogee tech for Apogee....

    I will explain jitter as best as I can for you..

    Jitter is a change in the way that the waveform is resampled within the translation period in the A/D section or even the D/A section of any converter. Jitter is a jump in the timeframe of the pulses within this process and not in the actual frequency of the samples. So you could have a series of 9 pulses per second which then turns to 10 pulses second very quickly and not have jitter...BUT if between the 9 pulses per second it varies to 9.5 or 9.002(etc etc etc) that is where jitter comes into play.

    If you were to take a word clock output into a scope and measure it you would see the square wave of the frequency being used and if there was mass amounts of jitter you would see the square wave start to look distorted..this is basically a way to measure jitter...but on the digital output you would put it to either a scope or an AP(Audio Precision) machine of some sort.

    Obviously Apogee is known for it's very ultra low jitter clocking so you are safe in that regards.
    As the A/D is the most crucial stage in your chain it is important to have the best possible signal at that point! If you were to have a weak A/D converter with lots of jitter, even a good D/A converter could not fix it as it is printed into the waveform.

    This is not something that can be seen, just measured with the appropriate gear from the digital output of the device in question.

    It is also very possible that a D/A converter will have jitter as well and the only way to solve that is to get a better D/A device!

    I'm not sure if the Benchmark DAC-1 has a dual clocking stage in it but it's a good thing to look into as it will help buffer and clean the digital signal.

    The Apogee Mini-Dac has this and is actually a great D/A unit to get in that regards.

    Now, the Big Ben will improve any device as it's jitter is pretty much unmeasurable! It's too damn low! Seriously! You would benefit greatly BUT with the Rosetta you would have to have the Big Ben clock from it as the Rosetta is a master clock only!

    This is not such a bad thing due to the fact that the Big Ben actually has what is called ALF(Adaptive Loop Filtering). This is where any clock being fed into the Big Ben is reshaped and cleaned up. This ultimately makes the clock as if it was Big Ben's own internal clock making it the clock being sent out of the Big Ben completely jitter free!

    Jitter can indeed cause your sound to be degraded as there are some converters that will happily degrade your audio without care!

    I do hope this helps explain or educate you on this matter and if you have any more questions please let us know!

    Cheers

    Opus :D
     
  3. Bri

    Bri Active Member

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    Hi Opus, I was hoping I'd hear from you. Thank you very much for your informative reply. :)

    So then, would there be a noticeable difference if I went from the Rosetta into the Big Ben, or is the Rosetta fine on it's own?

    Also, I was curious. Given your experience with Apogee's products, can you give me an honest opinion on the quality of the Rosetta's converters/how they sound, compared to Apogee's other converters?

    Thanks Opus
    --Brian
     
  4. Ethan Winer

    Ethan Winer Active Member

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    Bri,

    Opus gave you a good explanation, but I'm going to weigh in too with my opinion.

    I believe that jitter is a complete non-problem with modern digital gear. An answer to a question nobody asked. A solution for which no problem exists.

    Jitter is expressed similar to noise - as some number of decibels below the program material. Typical jitter figures are 110 or more dB below the program. And since it's present only when the signal is present, it is not only way softer than you'll ever hear but also masked by the main signal. Adding even 1/4 dB of EQ boost at any frequency will have more effect on the music than anything caused by jitter.

    --Ethan
     
  5. vinniesrs

    vinniesrs Active Member

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    May 12, 2003
    I would have to agree with ethan. Have you ever heard anyone complain about a noisy recording while music was blasting away at the same time?(I am talking about commercial recordings here :roll: ). I think that this, and other debates like it are important, but more so for the development of better stuff. I think that from one device to the next, marginal differences in one area dim in importance when compared to other more important things, such as placement of mics.
    The bottom line is that millions of records have been sold on recordings from black face adats in the early 90's, and no one is refusing to buy them today.
    I am not suggesting we ignore this stuff, as it's great to know, but the most important thing to remember here is that the ends justify the means.

    Just a thought.
     
  6. Bri

    Bri Active Member

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    Hey guys, thanks for your input....encouraging.

    I guess what it comes down to is that I'm trying to make sure my electronic equipment choices are capable of producing a truly professional quality of sound...relative to the electronics used...converters for example. Especially considering I mostly record acoustic instruments.

    Considering my budget/finacial status, I'm a little neurotic about making sure I've made the best decision/compromise. So, do you think the Rosetta was a good choice in that respect?

    I'm just not completely sure about the difference between jitter and converters in regards to their negative effects on the incoming signal when hearing things like, "this AD converter sounds clearer, tighter, better dynamic range as opposed to this one, etc., etc." For example, what exactly is the difference between a $1000 2-channel AD converter, and $5000 2-channel AD converter in regards to sound quality?

    Thanks --Brian
     
  7. Opus2000

    Opus2000 Distinguished Member

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    Apr 7, 2001
    Well, you have to look at the functionality offered by the device over the other devices.

    Some may have more analog functionality combined with some special circuitry(such as Apogee Soft Limit or the like there of!)

    When comparing converters you really have to look at the overall operation of the unit more so than the coverters to be honest.

    Remember that the converters are only one stage and not entirely the most crucial. It's the design around the converters that make the difference. Depending on what Op Amp you may use or what form of capacitor inline with some resistors to truly open things up.

    That coupled with the power supply in terms of filtering out the bad current or noise induced in the line will help make a product work better for you..

    Now, in terms of sound over the other Apogee converters vs. the Rosetta?

    Well, the AD-800SE, Trak2 and the PSX-100SE are all the top of our lines.

    After those comes the regular AD-800, regular PSX-100, Rosetta 2 CH A/D and the Mini-Me.

    Now I did not put them in any specific order here..just listed them.

    With the new products coming out you can be almost gauranteed that they will sound as good as the other products or even better. Newer technology and newer ways of designing converters help in this fashion!

    In the terms of what Ethan and Steve said...absolutely! I'll babble all the technical terms and they'll put it in laymens terms for you! :D

    HTH

    Opus :D
     
  8. Ethan Winer

    Ethan Winer Active Member

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    Brian,

    > I'm trying to make sure my electronic equipment choices are capable of producing a truly professional quality ... Especially considering I mostly record acoustic instruments. <

    I assure you the room you record in has 100 times more impact than any amount of jitter. Getting your room acoustics in order should be a far higher priority than just about anything else in your studio. What is more important:

    1. jitter noise 120 dB below the music

    2. 0.0001% versus 0.001% slew rate distortion

    3. a frequency response that varies continually by 20 dB throughout the entire bass range

    > when hearing things like, "this AD converter sounds clearer, tighter, better dynamic range <

    That sounds like a lot of jaw-boning by people who would likely hear no difference at all in a true double-blind test.

    > what exactly is the difference between a $1000 2-channel AD converter, and $5000 2-channel AD converter in regards to sound quality? <

    $4,000 less in your bank account.

    --Ethan
     
  9. Bri

    Bri Active Member

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    Thanks Ethan.

    I'm still working hard on the room. :)

    --Brian
     
  10. vinniesrs

    vinniesrs Active Member

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    May 12, 2003
    Well put Ethan!

    I have often heard the statement "your studio is only as good as it's weakest link."
    In the case of most places I've encountered, the room is by far the weakest link. My own place included. You can get around this to some extent. I mean it is possible to make a decent recording with sloppy acoustics.
    In most cases however, I think there are too many gear heads complaining about marginal technical advantages, when it is literally impossible to appreciate the differences from within your environment.

    I did a recording a while ago for a band who had a limited budget. I don't have clip on mic's at the studio, and I wanted to use them for this demo because of time constraints.
    I rented the mics from a music store in kitchener, I checked the first one to make sure that the clip was present, and returned to the studio. When I opened the rest of the mics I found that no clips were included, except for the one I had checked. I called the store to see if they had clips, and the rentals manager there confirmed that he did.
    When I asked why they were not included, he proceded to lecture me on subsonic transmissions from the clip.

    My point is simply that many techs like this one, are so strung up on the technical aspects of this field, they can quite easily lose perspective of what is practical in a given situation.
    I was doing a four song demo for $400. I didn't need to spend an hour and a half trying to squeeze booms into a super tight drum setup, but thanks to genious boy, I did.

    I'm not an acoustics expert as you are Ethan, but I know and understand the benefits of acoustics, and I've found that the majority of those in my area find it to be less crucial.
    It must be because flashing lights are too much fun! :D
     
  11. Ethan Winer

    Ethan Winer Active Member

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    Steve,

    > In the case of most places I've encountered, the room is by far the weakest link. <

    This is for certain, and far too many engineers have no clue how bad their rooms are or how much the room influences everything they do. Arguably much more than which gear they use.

    I've been accused of turning every thread into a pitch for room treatment, and that's not entirely wrong. :) But I truly believe this is the biggest problem for most folks.

    > I mean it is possible to make a decent recording with sloppy acoustics. <

    Sure, just as you can make a decent recording with mediocre mikes, pres, and loudspeakers.

    > When I asked why they were not included, he proceded to lecture me on subsonic transmissions from the clip. <

    Yeah, much easier than admitting he screwed up!

    > It must be because flashing lights are too much fun! <

    No question that acoustic panels and foam are not nearly as sexy as electronic gear. Just like motor oil and gasoline are not as sexy as a new Corvette. But without oil and gas, the coolest and most expensive car in the world won't get out of your driveway.

    --Ethan
     
  12. Kurt Foster

    Kurt Foster Distinguished Member

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    To put the thread back on topic,
    Bri,
    I myself have heard the difference good clocking can make with Blackface ADATs. Once by clocking them to a Yamaha 02R console, and once by clocking them off an Apogee PSX 100.. good clocking does make a difference IMO. Almost any experienced recording engineer will agree. It is only the occasional "heretic" that will dispute this... Kurt
     
  13. TedB

    TedB Guest

    Opus, maybe you can tell me what I was hearing when I a/b'd my midiman audiophile converters against the Korg D1200 tabletop recorder.

    I kept the chain identical, recorded to both devices simultaneously on the same take. Same bit depth, sampling rate, etc.

    Then auditioned both files from the same D/A on the audiophile.

    The files created by the Korg just sounded so much clearer, mostly on vox. But even the guitar tracks were better.

    Can jitter account for muddiness? Or is it some other part of the converter?

    A buddy and I also did a more informal test with his HD24 and the Korg, and I found the HD24's tracks even cleaner than the korg. We attributed it to the converters, since we tried to keep everything else constant.

    What part of the converters could account for this? Am I just hearing things?

    thanks

    ted
     
  14. Kurt Foster

    Kurt Foster Distinguished Member

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    Actually those ads you are running in the magazines (Mix, Pro Audio Review, EQ ) look pretty damn sexey to me. (sh-wing!) I have to admit that the mini traps certianly do look much better than foam products which are for the most part butt freakin' ugly.. Foam (usually) charcoal gray, darkens the room and after a few years degrades, crumbles and just get uglier. MiniTraps, sleek, trim, fits into the decore of almost any room.. the good looks last and gives your room that "professional" look..
    Yep! Old dogs can learn new tricks..

    But I still think good clocking makes a big difference.. ! :D heee heee ... Kurt
     
  15. Bri

    Bri Active Member

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    Thanks Kurt. :)

    --Brian
     
  16. Ethan Winer

    Ethan Winer Active Member

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    Kurt,

    > Yep! Old dogs can learn new tricks.. <

    Aw gee, thanks. But now how can I counter with the importance of double-blind testing for jitter? :D

    Ted: as far as I know, the only thing jitter contributes is noise, and very low level noise at that. I know some people say they hear all kinds of stuff change when they switch clocks: imaging, clarity, low frequency detail, yada yada. I'll reserve judgement until I've personally sat in on a double-blind test. But I can think of no logical reason why normal amounts of jitter - typically 110 dB or more below the program - could have any audible affect.

    --Ethan
     
  17. Kurt Foster

    Kurt Foster Distinguished Member

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    Ethan, If you have any data from double blind tests that supports the contention that jitter is in audible, I would be happy to consider it and perhaps change my position. I acknowledge that the "placebo effect" can influence ones impressions. But until I am shown that my ears are fooling me on something, my tendency is to believe what I hear.. :tu: Kurt
     
  18. TedB

    TedB Guest

    Ethan, Opus or anyone:

    Is there anything else beside jitter that can cause a converter to sound clearer?

    In other words, what are all the factors/elements contributing to a converter's quality? Is jitter the only one? How about aliasing and all that fancy stuff?

    In my test, the difference is significant to my ears, even though it wasn't a truly double blind test. I'm looking to understand why, if it's not jitter...

    When I get the time, perhaps I'll post the two files...
     
  19. Ethan Winer

    Ethan Winer Active Member

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    Ted,

    > what are all the factors/elements contributing to a converter's quality? <

    All of the usual [audio] suspects, plus maybe one or two more specific to digital audio. So there's frequency response, THD and IM distortion, slew rate limiting which is just another type of distortion, noise - several types - and [digital only] ringing caused by filters, and jitter. There's also phase shift, but I've never seen or heard evidence that phase shift alone is audible. I probably missed a few things.

    The real problem is that all of this stuff can be measured easily enough, yet some people claim to hear degradation even when the measurements show that should not be the case. Which is why double blind tests are so important. Not that you aren't hearing something wrong. Maybe I should add to the list above that sometimes gear breaks, so even if the stated specs are fine, that particular gear may not be meeting its specs.

    --Ethan

    [ August 18, 2003, 02:20 PM: Message edited by: Ethan Winer ]
     
  20. Opus2000

    Opus2000 Distinguished Member

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    Indeed jitter does not attribute to sound differences in any way. It's all in the way that the clocking is shaped and how it's response is in the long run.

    As Ethan stated there are differences of the circuitry around the converters such as Op Amps and resistors.

    Certain resistors will indeed cause some coloration or lack there of. Also some Op Amps may have a higher DC offset than others causing some problems in the audio.

    The cheaper the converter the lower the quality will be. There are factors in the designs of converters which do indeed change the characteristic of the sound.

    Now, we were blown away here at Apogee when people said that the Big Ben clearly changed the sound of everything. We attribute this to the clocking having a "bell" curve, thus coming up with the idea of the name Big Ben as it is what the Big Ben is! A big bell for the clock itself!

    This bell curve is very smooth and does not spike or randomly change at variations.

    This can attribute to a very clean sound.

    So in the long run the clock has a crucial stage, which helps in the jitter level, but again as we stated here, jitter has no change in the audio quality of the way we hear it.

    HTH

    Opus :D
     

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