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Questions about Soft Faders

Discussion in 'Recording' started by patrick_like_static, Nov 28, 2007.

  1. These are questions I have concerning "in the box" mixing, since I've never heard them answered satisfactorily before:

    1.) Is it still (or was it ever) necessary to keep software master faders at unity in order to prevent signal degradation? Hypothetically, if a track fader and master fader both set at 0.0 results in a signal of -0.1, is there any difference in this scenario versus one where the master fader is at -8.0 and the track is at +8.0, or versus one where the master fader is at +8.0 and the track is at -8.0?

    2.) As above: a lot of times in Reaper and Acid Pro (and previously Nuendo) when I have my master fader well below unity with tracks and/or bus levels above 0.0 to compensate, the individual track/bus meters go into the red, whereas the master meters are still in the clear. Are these true overs? I don't hear clipping but I wanted to make sure this wasn't the case.
     
  2. Cucco

    Cucco Distinguished Member

    Good questions.

    1 - leaving your soft faders at unity while tracking is a good idea. During mixing, move them all you want.

    2 - Each channel's bus will usually allow you some overs (operating at 32 bit float in many softwares) without clipping but you are usually forcing it into your softwares basic brickwall limiter.

    3 - Your software's master fader is the *last* piece in the signal chain. That means if you're clipping the main bus and it's forcing your software to use its default limiter - lowering the main fader won't change this. It will still be clipped and limited, but with a lower maximum output. Try feeding horribly clipped samples into your main bus and lowering it by 3dB. The output wave will look flat as a square, but 3dB off of the ceiling.

    That all being said - leave the master fader alone. Think of it as a volume knob while you're mixing or recording. (Easier to turn down than the knobs on your monitors...)

    As for the track faders, feel free to use them as you would a normal mixer. If you see clipping though...back them off. You may not "hear" the clipping and you may not see it in the master bus, but that's because it's automatically being limited. The only way I'd ever let a limiter touch my stuff is if I turned it on and told it to do so.

    Cheers-

    J.
     
  3. IIRs

    IIRs Well-Known Member

    Huh? What basic brickwall limiter are you referring to?

    If your software uses floating point maths (which most do these days) then no there is no difference beween running two faders at unity and running one at +8dB and the other at -8dB. Unless you consider floating point errors in the multiplications of course, but that is not likely to be significant. There will definitely be no clipping or limiting going on.

    You can verify this if your DAW will export 32 bit float files. Import a short audio clip, boost its gain by a ridiculous amount like 50dB so you distort the mix bus horrendously (turn down your monitors first!) then export a 32 bit file. Re-import that file, and turn the gain down by the same amount you boosted it before: notice that the sound cleans up again, rather than just ending up quiet and distorted. ie: that distortion you were hearing was only occuring when the audio was converted to 24 bit integer to feed the soundcard drivers, and the 'clipped' peaks are still intact so long as the audio stays at 32 bit float.

    That said, I still mix with my master fader at unity all the time. This is partly out of habit as thats how I work with analog desks, partly because my DAW only allows mix bus plugs to be pre-fader and I like to use metering plugs there, and partly because all bets are off when plugs enter the equation: your plugs might clip overs even if your host does not (depends on how the plug is coded)
     
  4. Cucco

    Cucco Distinguished Member

    Try bouncing the clipped files you're talking about down to 16 bit.

    They're limited. The software does this (in most cases) to avoid the clipping.

    Yes, if you remain at 32 float, this won't occur. But, the last time I checked, Red Book doesn't allow for 32 bit float CDs. You're going to have to cope with the amplitude at the 16 bit level at some point, it may as well be in the initial mix phase.
     
  5. IIRs

    IIRs Well-Known Member

    I'm not aware of any DAW software that limits rather than clips, unless you specifically tell it to. :?
     
  6. Cucco

    Cucco Distinguished Member

    CEP does - at least it used to. I don't know about Audition.
     
  7. IIRs

    IIRs Well-Known Member

    You sure about that? I find that hard to believe. Soundforge doesn't. Neither does Cubase, I'm pretty sure Logic doesn't, and Tracktion definitely doesn't.
     
  8. Cucco

    Cucco Distinguished Member

    Yup.

    It's been a LONG time since I've intentionally or even accidentally driven the mix into the digital bus so hard as to cause this, but one specific (and tragic) incident comes to mind and CEP was kind enough to avoid square wave syndrom for me without the use of an add-in brick wall.

    In any case, even without the brick wall (which I'm inclined to believe your statements), driving too hard into the digital mix bus is a bad idea. The master fader still resides as the last piece in the routing chain (some software will allow you to adjust this, but I can't think of any scenario where this would help in this instance).

    Essentially, it would still clip, it would just do so at -3dB if the fader were dropped by as much (clipping being defined as any 3 consecutive samples at -0dBFS - or 2 for that matter depending upon which definition of digital clipping you subscribe).
     
  9. IIRs

    IIRs Well-Known Member

    No it doesn't clip. Floating point audio provides effectively limitless headroom: the peaks are still intact, even if they clip when they hit your soundcard.
     
  10. Cucco

    Cucco Distinguished Member

    We're still talking about different things here. You're assuming the product is staying at 32 float. I'm talking about when it is bounced (the inevitable outcome of all current 32bit float projects).

    When bounced, it will clip. Period. (Again, clipping being 3 sequential 0dBFS samples)

    In theory, what you're saying is 100% accurate (or darn near it since 32 float can indeed be clipped, but only with such extremes), however, in practice, it is NEVER a good idea to overload the mix bus for any reason whatsoever.
     
  11. IIRs

    IIRs Well-Known Member

    I'm not assuming anything. The question was about two faders in a DAW app, and every DAW I know of uses floats when mixing. So its basically impossible to clip, and mixing with the master fader at -20 or wherever is perfectly valid assuming you know that all your plugs are well behaved in this regard. The outcome (when bounced to 16 bit) will be exactly the same as if you mixed with the master fader at unity and all your channels 20dB lower.
     
  12. Cucco

    Cucco Distinguished Member

    This is simply incorrect.

    Yes, when mixing an audio file in common, modern DAWs, the mix bus stays at 32 float and thus anything mixed, even past "clipping" retains its resolution.

    However, when you bounce this wave down to 16 bit, the bus does not automatically normalize so that your loudest peaks are now at 0.0 dBFS. If it's past 0dBFS on a 16 bit scale, it's a clip. Period.

    Your example of cranking up the faders and mixing past sanity, then bouncing down and then reducing the amplitude and having your resolution is NOT true if you bounce down to a resolution other than 32 bit float.

    I just did it 2 minutes ago and guess what - a clipped square wave of a file.

    This is simply not true.

    Again, only if you remain at 32 bit float. If you bounce to 16 bit (which you will), and the mix bus is clipped, you will not regain your resolution.

    I don't care what resolution the mix bus is at, when you bounce down to 16 bit, your audio will be ruined - period.

    Also, the Master fader is AFTER the mix bus in the routing in all current DAWs. The summing and bouncing occurs AT the mix bus. This means if you've clipped the mix bus (according to the 16 bit file that you're rendering) and then the master fader is down 20dB, you'll have a clipped wave which happens to have 20dB of headroom above the clips.

    Have you actually tried what you're talking about?

    If what you're saying were true, my mastering work would be TONS easier since most of the clipping I get is NOT from misuse of limiters, it's from people mixing too hard into the DAWs summing bus.
     
  13. IIRs

    IIRs Well-Known Member

    Yes of course I have tried it. Have you? You are dead wrong.

    The audio streams are all mixed using floats, then scaled by the master fader, again as floats, and only then will they be truncated to 16 bit when you bounce. ALL the math is done using floats (with practically infinite headroom) so as long as you stay below 0dBFS at the output your 16-bit bounce will be just fine. Mathematically it does not matter whether you scale the individual tracks before summing, or scale the mix bus after summing, so long as all those processes use floating point math (which they do).
     
  14. Cucco

    Cucco Distinguished Member

    The proof is going to have to be in the pudding.

    As soon as I'm free this weekend, I'll upload 3 graphics.

    Graphic 1 - Control. This will be a 2 track file which is bounced from a multi-track where there is no clipping what so ever (or exceeding the 0.0dBFS mark)

    Graphic 2 - Pushed Track Faders. This will be the 2-track graphic from a multi-track file whose faders have been pushed past the point of clipping and then bounced to 2 track.

    Graphic 3 - Pushed Track Faders - Lowered Master Fader. This will be the graphic of a 2-track bounced file from where the track faders were pushed past bus clipping and then the master fader was lowered to compensate.

    If that doesn't clarify, I don't know what will.
     
  15. Cucco

    Cucco Distinguished Member

    Okay...before I packed up the rig to take it on remote, I did this real quick.


    Picture 1 - Regular file - no clipping - plenty of head room

    (Dead Link Removed)



    Picture 2 - Same exact clip boosted 20 dB using soft faders and bounced to 16 bit - notice all the square tops

    (Dead Link Removed)


    Picture 3 - Same as above with the master fader lowered 20 dB and then after bouncing, normalized. Notice how similar it is to picture 2.

    (Dead Link Removed)
     
  16. Cucco

    Cucco Distinguished Member

    By the way, I put both 2 and 3 into Sequoia again and tried to lower the gain to regain my resolution...nothing but clipped peaks.

    My point is, the master fader has no purpose in being used to treat the entire audio file, it makes no difference.

    Use the channel faders to get the level you want. The master fader (just like on any real console) should really only be used as a volume knob.
     
  17. Cucco

    Cucco Distinguished Member

    I suppose in graphic 3, it would have been helpful if I didn't normalize it. But, now my computer is off and in the process of being packed up.

    It looked identical to its current only quieter. Still had clipped peaks all over the place even though the meters showed peaks of only -20dBFS.
     
  18. Cucco

    Cucco Distinguished Member

    Same is the case with my waves 2 and 3 - invert = silence.

    Perhaps the routing in Sequoia is more like an analog console. I can, after all, move the master fader to occur before the master bus, which would give me the same results as what you have. However, I cannot possibly think of a reason where this would be a positive thing.

    On an analog console, if you clip the channel, that's it. The same is the case with my default routing in Sequoia. Again, this can be changed, but why on earth would I want to?

    --EDIT--

    Well, thanks to 32 bit, if you clip a channel in Sequoia, that's not it. However, if you clip the master bus, then bounce to 16 bit, that is it.
     
  19. IIRs

    IIRs Well-Known Member

    No, it means Sequoia has no headroom at the mix bus, unlike every other modern DAW. Are you running the latest version?
     
  20. bent

    bent No Bad Vibes! Well-Known Member

    I think there are two different arguments happening here.
    So, I did the test as well with a 48k/24bit Vegas session with all fx chains bypassed.
    Each result was rendered to 44.1/16bit.

    Image 1 - Multitrack session, all faders +12, all files normalised per track, Master at 0.

    devilskincrushed12dB.jpg

    Image 2 - Same session, same settings, Master at -27.

    devilskincrushed12dBmaster-27dB.jpg

    Image 3 - Results of both.

    VegasDevilskinbothfiles.jpg
     

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