Digital Level Setting

Discussion in 'Recording/Live Sound' started by decay-o-caster, Jan 4, 2005.


  1. decay-o-caster

    decay-o-caster Member

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    I LIKE analog VU meters. I know how to set levels in analog - you want it to sound hot, get it into the red, but don't peg the needle.

    I don't dig digital. I'm paranoid about digital - if it gets into the red, it's into digital clipping and becomes an abomination in the eyes and ears of the elders.

    But the digital meters in apps like DP4 just don't give me the sense of control I used to have using VU meters in the good old analog days.

    So what do I do? Get an analog board, figure out where unity gain into MOTU828 / DP4 is, and run everything through it? Live with under-recorded digital recordings? Or just deal with a little bit of bouncing into the red? :confused:

    :(
     
  2. MichaelK

    MichaelK Member

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    This is the most glaring inherent difference between digital and analog: there's no saturation allowed in digital. That's just the nature of the beast.

    A friend of mine ignores the meters entirely unless he actually hears something he doesn't like. Sometimes the quick blip of a transient spike overloading just a touch here and there is not really audible. Then again, sometimes you might think it's inaudible while you're tracking, only to hear later that it was more audible than you thought.

    This is why paying for good A/D converters makes sense. The better ones allow you to push a little and sound pleasant, like tape. I usually use the "Soft Limit" feature on my Apogee A/D when tracking, which gives me a little more room to push. It doesn't prevent overloads entirely, it just makes the ceiling a little more flexible. I don't really hear it working.

    Sometimes compressing to tape with an analog compressor can give you the saturation you're looking for. If I want an uncompressed sound, sometimes a little bit of limiting keeps the clipping in check without being obtrusive. But if it isn't working for me, I just keep the input gain down where it has to be and deal with it in the mix. C'est la vie. Unless it's really WAY down there, you still use enough bits for plenty of detail. I'm told that film orchestras are recorded at very low levels to avoid any clipping whatsoever, because retakes of a large orchestra are very expensive.
     
  3. GaryNattrass

    GaryNattrass Member

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    People also get paranoid about digital and think that they have to go all the way to the top all the time because they are used to tape and getting the best sig to noise.

    You do not need to peak all the time unless it is to produce a final master and besides a peak compressor limiter or mastering tool will allow you to do this without clipping.

    As a guide the following applies when a 1khz signal is fed at odb .775v.

    0 level on VU is -4db

    0 level on digital full scale is -18db

    0 level on PPM is 0db

    Taking in to acount that if you are peaking on a VU at +3db's then the equivalent level on a digital full scale meter is -11db's beyond that is your headroom so if you are peaking around the
    -10 mark then that is about the same as you are oin a VU meter.

    As a side note Sony gear works at -20 for full peak, this was done to stop the analogue engineers constantly clipping the Dash machines when they first came out.

    www.elementalaudio.com

    Has a good digital full scale meter that you can download free for Pro Tools.

    Also dont get paranoid about noise as the reverse is true on digital audio, the lower that you modulate then the less noise that there is. There are also 90db's of dynamic range so for most music applications there is lots of headroom available.
     
  4. MichaelK

    MichaelK Member

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    Gary just made that stuff up; don't listen to him. :D

    I know what you mean, though. If you see that little green bar going only 1/4 of the way up the stick you feel in your gut that you must be missing something, even if your brain tells you it's OK.
     
  5. LSchefman

    LSchefman Supporting Member

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    I have old-fashioned analog VU meters on my console, and when I set my levels, I can easily correlate them to the bar meters on my MOTU 1296.

    Actually, Michael's right about converters, I go into the red occasionally on peaks with the 1296 and it sounds fine as long as I don't overdo it.
     
  6. GaryNattrass

    GaryNattrass Member

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    I also found that hitting the red led on my Fostex D160 didnt cause any probs, I think the digital stuff is a bit more forgiving these days.
     
  7. Unburst

    Unburst Member

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    If you use the audio monitor window in DP (shift-A) then go to the mini-menu you can select the range of the meter, set it to 6db, this will give you a more accurate metering for the input.

    Now set your levels so you are peaking in the top 3db without the peak light coming on.

    Basically the more level you can get into an A/D the better, if you are recording at say, 16 bit resolution, it is only using 16 bits at 0db, for every 3db lower than that you lose 1 bit, this is why it's better to use 24 bit and dither down, it gives you more leeway in the recording level, but 0db is a hard maximum, there is no red zone in digital, if you go over 0db it will distort.
     
  8. decay-o-caster

    decay-o-caster Member

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    Martin - thanks, Mr. Tech Support! The 6dB trick might just be exactly what I needed.

    Most obliged...
     
  9. Unburst

    Unburst Member

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    My pleasure, any time you've got a question, feel free to hit my email.
     
  10. amper

    amper Member

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    Heh...the one subject that none of the books I've seen cover *at all*.

    Bottom line...calibrate your VU meters so that 0 VU ends up somewhere in the area of -14 dBu to -20 dBu.

    I'm still trying to find out if it's better to track at/near your intended output level or as close to 0 dBFS as possible. If you're pulling faders back on a hot track, does that make the CPU work harder than if you're leaving the faders at 0 dB, and does that lead to better sound?

    The few recommendations I've seen say to peak your tracks in the -6 dB to -3 dB range to ensure against overruns.

    There's a few good articles on http://www.digido.com/ about recodring levels. I'm following the recommendation there relating to the "K-Scale" metering. My system is calibrated so that a -20dBFS RMS pink noise signal comes out at 83dB. Then I mix with the monitor gain dropped by 6dB.

    With 24 bits of resolution, it's not always necessary to run your tracks as hot as possible...
     
  11. Bassomatic

    Bassomatic Silver Supporting Member

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    It's better to track (not necessarily mix) as close to 0 dBFS as you can (without risking overs). Typically, you want to use as much of your bit depth as possible (although it's nothing to lose much sleep over if your converters and software are up to snuff).

    As to the CPU question, faders are meant to be moved. Pull 'em back, push 'em up, and only sweat the master buss.
     

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