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low level clipping and db level problems tt pro

Discussion in 'Recording' started by kepeb, Apr 12, 2009.

  1. kepeb

    kepeb Guest

    hi all.
    after many fruitless hours of research into this i have decided to irritate some of you with some questions :)

    i am running a windows xp cubase or reaper based setup with a focusrite saffire pro 40 as the interface.
    i also have a focusrite twintrak(TT) pro with the a/d card installed.

    using the twintrack i am sending both preamp signals via spdif to the pro 40 then into windows.
    now, my concern is:

    if i set the gain to a good level on the TT its way too big in the pro 40 interface window. i have come down on the pres and retried with better results but still occasional recorded clipping in the daw.
    if i keep pulling the pre gain down arent i reducing the s/n ratio in a bad way?
    am i missing something?
    any thoughts would be greatly appreciated :)
     
  2. Guitarfreak

    Guitarfreak Well-Known Member

    Two things...

    1. Where are you keeping your levels? Where do they max at?
    2. Internet traffic is the number one cause of unexpected clipping.

    So if you have your levels MAX at -6dB or lower and OCCASIONALLY experience recorded clipping, then try disabling your internet connection before you record.
     
  3. kepeb

    kepeb Guest

    well there is no networking active or even installed to my knowledge on my music machine,
    also, when i turned the pres gain down the remaining noticable clips were only on the volume peaks. this suggests to me that its audio triggered and not unrelated interference. so i would think i can rule that out maybe.

    but your first question..
    i have had nice sounding levels through the built in headphone monitor right up to 0db(fs) but cant get near that without overloading the saffires input through spdif. this means i end up bringing down the trim to -50% of possible clean sounding gain.

    i was under the impression that achieving levels as hot as possible from the initial recording was desirable (obviously before clipping) to keep noise to a minimum?
    i also thought 0dbfs (or full scale) was the peak limit i should aim for (but not exceed) in digital recordings. seems possible to get working levels of about -20dbfs or so but this seems odd to me.

    also when i adjust the preamps gain right down low enough to avoid overloading my saffire, the analog meters barely even flicker, this cant be right can it?
     
  4. Codemonkey

    Codemonkey Well-Known Member

    "2. Internet traffic is the number one cause of unexpected clipping."
    On a technicality I'd call it dropouts (pops/clicks).

    Reducing the preamp gain actually won't affect the signal/noise ratio much. Not to the point where it'll become unusable.
     
  5. TheJackAttack

    TheJackAttack Distinguished Member

    First to confirm. You are coming out of the preamp via digital spdif into the interface. From the interface you are coming out via firewire into the DAW.

    Ok. If you are coming into the interface digitally then you should not experience any clipping in the signal at all. If it were going to clip it would do so at the preamp. An exception would be if you were adding compression or other FX within the interface that provided additional gain.

    Within the DAW itself you would be able to push the gain up enough to clip but if you left it at the generic setting while recording it wouldn't clip.

    If you had firewire buffer issues then that would cause pops or clicks or dropouts. Also inre pops and clicks, you need to make sure the interface and the preamp knows themselves which one is the clock master and which is the slave.
     
  6. kepeb

    kepeb Guest

    so if i drop the level on the pre gain then the noise level or s/n wont increase by the same amount as the drop in gain?
    ie. if i drop the input by -20 from 0dbfs i wont have a noise floor higher by 20dbfs on the output?
    thanks
     
  7. Guitarfreak

    Guitarfreak Well-Known Member

    Nahh man if you are aiming for the 0dB mark as a target then you are doing it wrong. In digital recording the 0dB mark is the point at which the processors cannot code the incoming signal correctly, and you are left with varying degrees of holes/irregularities in the signal. Depending on the converter the signal will start to audibly clip at a little bit under or over the 0dB mark. So you should aim for -6dB to -10dB for more headroom in your recording and that's MAX level, not AVG level. The difference is that an average level of -6dB might go to -2 or even 0dB at certain points when the musician gets excited. So you want the highest peaks to be well under 0dB.

    Tracking is arguably the most important point at which you should babysit your levels, because afterwards you can always add more gain/volume, but if you record a clipped track..well you might as well scrap that take and go again because you can't do $*^t about it. At least not at my experience/skill level.

    If you are still confused look up gain structure. http://www.recordingreview.com/articles/articles/181/1/The-Basics-Of-Setting-Gain-Structure/Page1.html
     
  8. kepeb

    kepeb Guest

    thanks guys,
    yea 0dbfs would be absolute peak and not to be exceeded, as i said earlier. i just want to make sure i get a decent level from the off which is close to maybe -6dbfs
    i am assuming that the ttpro's LEDs will show peak levels, this is what i was going by when tracking. if not, how high could the unseen peaks potentially be?

    and yea, its tt pro - saffire pro(via spdif) - daw (via fw w/no effects)

    just that tt pro can be reading -18 on the LEDs and barely moving on the analog meters but still come to the saffire too hot.
    the levels sound ok recorded when i have it set this low but it seems less than ideal
     
  9. TheJackAttack

    TheJackAttack Distinguished Member

    Your thinking in regards your s/n ratio is wrong. The noise ratio will be the same regardless of your fader level-it is just that, a ratio. If you track at low levels and then later boost them in the DAW you are also boosting the noise as well. What can change is if your mic level is low enough that it doesn't pick up physically as much extraneous noise. What isn't recorded can't be boosted. Things like self noise of a mic or a preamp are just going to be a given. That's why quality gear is expensive etc etc.

    With regard to tracking digitally, you want your peaks to be in the -10 to -6 range. This gives you headroom to work with later in the DAW. Back in the analog tape days if you pushed into the clip zone it wasn't necessarily bad. In digital, it's real bad.

    Gain staging is generally the same regarding digital vs analog as long as you follow the proper headroom logic (-6 peaks max). Your DAW fader shouldn't require tweaking until you are mixing as long as your preamp is set properly. Leave it as it defaults which is usually it's version of Unity. Don't worry about how it looks visually if the track sounds good. As a side note, the metering next to the fader is not the number to look at while tracking per se. Look at the number below indicating the boost/cut you are providing with the slider. That number should be 0 for tracking purposes. The right side meter is clipping out then turn down your preamp.

    The TT Pro has a compressor on it. Turn it off and see if your problems go away. If so then you are not setting the levels of your compressor properly. Which is not uncommon at all.
     
  10. kepeb

    kepeb Guest

    thanks very much.
    i'll play around some more tomorrow,

    to clarify,
    all the effects are off, if i go into the TT and ignore what it reads meter wise, ignore what the saffire interface says meter wise too, then adjust the gain on the preamp so i get highest peaks at under -6db in my DAW (also ignoring the DAW fader position at the tracking stage, which is 0db)?
     
  11. Guitarfreak

    Guitarfreak Well-Known Member

    No you don't ever want to ignore anything. Read that link I posted before, because it will explain in greater detail what we are saying. Your DAW reading is relative, a level of -6dB can be achieved any number of ways. You can run your first preamp at max and then cut it 30 dB at the next link in the chain. The goal is separating the load evenly across the board and ending up with -6dB attenuation in your DAW with the fader at 0dB (unity gain). If you can achieve this then you can pretty much record anything in any situation given the right gear.

    From your earlier posts I get the feeling that you are trying to push your initial preamp too hard and then cut it back somewhere downstream. Which is the whole reason I posted gain structure. Read it, because once I learned that, I was able to step into a studio that I've never been to and cut a demo of my friend's band with confidence.
     
  12. kepeb

    kepeb Guest

    hey, cheers.
    I'm thankful for your help and have read the link, it echo's much of what i have read before and have made routine gain structure since (when using other inputs on my saffire 40 directly, this is not an issue and i get good levels and good readings). but is not really addressing the issue i had earlier....

    i have the trimmer turned way DOWN on the TT.
    both displays on the TT read as seriously low levels.
    then it clips in the DAW

    when i said 'ignore' i was referring to the fact that the needles dont twitch and the lights barely even come on the LED peak meter(thats -40 odd below). i normally expect to see some life in my other pre's when tracking
    so my fear was that i would be doing the reverse of what you said.
    if i am feeding a really low preamp signal into the daw then have to boost it later surely there will be more noise?
    apologies, i dont think i explained myself very well
     
  13. TheJackAttack

    TheJackAttack Distinguished Member

    Within Reaper, what are you using for your source input? You can a heap of gain if you aren't choosing spdif right at this point.
     
  14. Guitarfreak

    Guitarfreak Well-Known Member

    "I think I just the whole thing, is that bad?"

    think you missed a word there chief. 8)
     
  15. TheJackAttack

    TheJackAttack Distinguished Member

    ....insert an arbitrary "add" anyplace you find appropriate....
     
  16. kepeb

    kepeb Guest

    well once ive gone into reaper and set up the input theres only one choice for spdif (well 2 channels) thats it.
    as i said. the levels are huge already by the saffire control screen, thats before reaper.
    so its something between the two focusrite units.

    nevermind, i think i'll probably mail them if i cant get it sorted.
    thanks for your help
     
  17. TheJackAttack

    TheJackAttack Distinguished Member

    I looked at the pdf manual for the Sapphire 40 this morning and it looks like a similar control gui as the RME totalmix. I am not nearly as familiar with totalmix as I should be but through the manual and trial and error I'll get it whipped. I have figured out that it can get pretty complicated in a hurry but ultimately it is all gozintas and gozoutas.

    I think that as long as you can get a good strong track with no clipping regardless of the visual on the gui then you have a place to begin your own experimentation. In a perfect world I'd have your piece of gear and be able to walk you right through one click at a time.
     
  18. kepeb

    kepeb Guest

    i get ya,
    its difficult to assess a problem properly when you cant see it, and its so specific. theres always a chance it was a common problem with a certain unit (ala focusrite) or even a simple case of me overlooking something.
    i had a play this morning and its still the same.
    im not sure exactly how to measure the signal and be sure im getting the best levels(with the meters reading like they do)

    any suggestions for a good way i could compare a signal once recorded besides just me havin a listen through my cheap monitors?
    i thought about using a very quiet source with 3 of the same mic through different pres into the daw. is there a better method?
     
  19. Guitarfreak

    Guitarfreak Well-Known Member

    Does the unit in question have a clip LED? If so just boost the signal until it lights up, then back it off about 10dB. That's the best way to do it without a dedicated meter.
     
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