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Thread: Metering in digital domain

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    Quote Originally Posted by Ethan Winer View Post
    For proof, see the article I wrote for GC Pro's Audio Solutions magazine:

    [url: Audio Solutions magazine[/url]

    . . I also prove the same points with nulls tests in my hour-long [url...Audio Myths...[/url] video .....
    Quote Originally Posted by Ethan Winer View Post
    See my article and video linked above for more info on how to test this.
    Quote Originally Posted by Ethan Winer View Post
    , maybe 1.5 Million views on YouTube .....[url....A Cello Rondo....[/url]

    Newer render with much better quality:

    [url....A Cello Rondo - HD Version....[/url]


    [url....Ethan's Audio and Music Bio Page....[/url]

    You would do well to read the article I linked to previously, and try to understand it. For extra credit, read and understand my [url....Perception....[/url] article, and watch my hour-long [url....AES Audio Myths.....[/url] video which proves these points.
    .... buy my book [url.....The Audio Expert....[/url] and read it all the way through.
    Quote Originally Posted by Ethan Winer View Post


    .... My book, which explores all of this stuff, was accepted by Focal Press....

    --Ethan

    seems borderline spamming to me.

    just sayin...

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    Hmmm, I think there are two divergent points of view here, both of which may have some elements of truth.

    First off, on his main argument, I'm with Ethan on this. Everything else being equal, there will be no difference in the sound of a recording with peaks up near 0dBFS and one 12 or 18dB lower. However, in the real world there are other things that come into play (or at least MAY come into play).

    The most compelling reason for lower levels is the avoidance of digital clipping. I hope we all agree that digital clipping is nasty, ugly stuff with no redeeming social qualities! I like to set my levels so the peaks are far enough below 0dBFS that, even when performance adrenalin raises the live levels, my recordings are safe. How much below 0dB? It depends on the performer and the musical style--but in all cases, I'd rather have slightly lower levels than a great take ruined by clipping.

    Second, there's practicality. If you're going to end up with 10 or 20 or 30 tracks to be mixed together and all of them are up near 0dBFS, then, in order to mix, you have to pull them all down to avoid clipping on the mix anyway. (I'll ignore for the moment mixing in 32 bit floating point where it matters a lot less since you can just normalise downwards). If you have to pull down all your levels anyway, why not start a bit lower?

    Third, if you ever use outboard effects with analogue inputs, then you need to feed out of your system at sensible analogue levels. Ingrained from my broadcast days, I'll align things with a constant tone at -18dBFS on my DAW and set levels so this is equal to 0dBu in the analogue world (and I do the same in reverse when setting up levels for recording from my mixer).

    Now, the dodgy bit (pun intended):

    I've never had a plug in that objected to levels approaching 0dBFS--but, if some claim to have ones that work that way I can't argue with them if I haven't tried the specific plug in. MAYBE this could be an issue with certain things that model analogue noise (or that are just badly written).

    So, do I believe that, in the digital domain, -18 sounds better than 0dBFS? Nope. Call me a sceptic. However, do I see practical (and measureable) reasons to keep levels comfortably below clipping? Absolutely.

    (And I don't see Ethan's contribution as in any way off topc.)
    That's what I do. I drink and I know things.
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    Quote Originally Posted by Dogbreath View Post
    seems borderline spamming to me.
    Thanks very much for your useful contribution to this thread.

    --Ethan

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    Quote Originally Posted by Bobbsy View Post
    The most compelling reason for lower levels is the avoidance of digital clipping.
    Of course, setting appropriate levels is a standard part of recording.

    I hope we all agree that digital clipping is nasty, ugly stuff with no redeeming social qualities!
    Actually, that's another myth. I did a test a few months ago where I intentionally clipped a recording of an acoustic guitar in the digital domain by raising the level to be 2 dB above 0dBFS. Then I lowered the volume to match the original for a fair side by side comparison. Yes, it sounds slightly different from the original - not unlike slightly overdriving analog tape - but it's not horrible as some would have you believe. I'll be glad to share the file if anyone cares. Or, better, just do the same experiment yourself in any two-track audio editing program.

    (I'll ignore for the moment mixing in 32 bit floating point where it matters a lot less since you can just normalise downwards). If you have to pull down all your levels anyway, why not start a bit lower?
    Well, don't ignore that altogether because it's hugely important and relevant to this discussion. But I agree there's no need to record as close to zero as possible. I've been arguing that for years. Even with "only" 16 bits, the noise floor is 20-30 dB quieter than analog tape. So recording with peaks around -10 or even lower is fine. I object only when people claim that recording at -20 dB sounds "better" than recording closer to zero, because it doesn't. Unless gain-staging is wrong somewhere else in the chain. Recording at conservative levels is mainly for safety and convenience.

    Third, if you ever use outboard effects with analogue inputs, then you need to feed out of your system at sensible analogue levels.
    Absolutely. I work entirely ITB, so this doesn't affect me. But outboard gear doesn't enjoy the luxury of 32-bit floating point math, so levels in and out definitely matter.

    I've never had a plug in that objected to levels approaching 0dBFS--but, if some claim to have ones that work that way I can't argue with them if I haven't tried the specific plug in. MAYBE this could be an issue with certain things that model analogue noise (or that are just badly written).
    Agreed, and I mentioned that earlier in this thread.

    (And I don't see Ethan's contribution as in any way off topc.)
    Thanks. And thanks for adding useful content to this discussion.

    --Ethan

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    Quote Originally Posted by Ethan Winer View Post
    Thanks very much for your useful contribution to this thread.

    --Ethan
    any time.

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    Quote Originally Posted by Bobbsy View Post
    Hmmm, I think there are two divergent points of view here, both of which may have some elements of truth.

    First off, on his main argument, I'm with Ethan on this. Everything else being equal, there will be no difference in the sound of a recording with peaks up near 0dBFS and one 12 or 18dB lower. However, in the real world there are other things that come into play (or at least MAY come into play).

    The most compelling reason for lower levels is the avoidance of digital clipping.
    I disagree. The most compelling reason for lower levels is to keep the analogue components in the signal path from producing distortion on input and, in the digital domain, to prevent inter-sample distortion at the DA output. Clip point is not necessarily the point at which distortion will be produced. It may manifest many dB BELOW clip point, depending on the quality of the components.

    This article by Thomas Lund sums it up nicely:

    www.tcelectronic.com/media/lund_2004_distortion_tmt20.pdf

    Quote Originally Posted by Bobbsy View Post
    I hope we all agree that digital clipping is nasty, ugly stuff with no redeeming social qualities! I like to set my levels so the peaks are far enough below 0dBFS that, even when performance adrenalin raises the live levels, my recordings are safe. How much below 0dB? It depends on the performer and the musical style--but in all cases, I'd rather have slightly lower levels than a great take ruined by clipping.
    Headroom is not a new idea and translates perfectly to the digital domain, as long as you know how to translate your dB scales and know how all of your digital and analogue gear relate to one another. The 0dBfs/clipping problem becomes moot as soon as you think in these terms. This, after all, was why the K system was developed. It just makes sense.

    Quote Originally Posted by Bobbsy View Post
    Second, there's practicality. If you're going to end up with 10 or 20 or 30 tracks to be mixed together and all of them are up near 0dBFS, then, in order to mix, you have to pull them all down to avoid clipping on the mix anyway. (I'll ignore for the moment mixing in 32 bit floating point where it matters a lot less since you can just normalise downwards). If you have to pull down all your levels anyway, why not start a bit lower?
    I agree but what about the distortion that might have been introduced by using preamps with inferior components that introduce distortion at 6 or 9dB below clip point? That distortion will still be there no matter how much you turn it down and at 20 or 30 tracks, the cumulative effect will kill your recording. You'll no doubt get harmonic buildup somewhere in the spectrum no matter what your digital levels are.

    Quote Originally Posted by Bobbsy View Post
    Third, if you ever use outboard effects with analogue inputs, then you need to feed out of your system at sensible analogue levels. Ingrained from my broadcast days, I'll align things with a constant tone at -18dBFS on my DAW and set levels so this is equal to 0dBu in the analogue world (and I do the same in reverse when setting up levels for recording from my mixer).
    A sensible view. Can't argue with that.

    Quote Originally Posted by Bobbsy View Post
    Now, the dodgy bit (pun intended):

    I've never had a plug in that objected to levels approaching 0dBFS--but, if some claim to have ones that work that way I can't argue with them if I haven't tried the specific plug in. MAYBE this could be an issue with certain things that model analogue noise (or that are just badly written).
    Exactly, so, if you don't have the time to null test every plugin (like most working engineers) the best thing to do is just keep your levels conservative and get on with the job which, of course, mostly entails LISTENING. It's amazing how the more listening experience you have, the less you need to know the results of a null test. Yes, they're interesting but for fuck sakes, who's got the time and the energy to test ALL of their plugins this way? How exactly will knowing the results make my mix any better? Did engineers of old refuse to work with an 1176 until they knew the results of a null test? Fuck that.

    Quote Originally Posted by Bobbsy View Post
    So, do I believe that, in the digital domain, -18 sounds better than 0dBFS? Nope. Call me a sceptic. However, do I see practical (and measureable) reasons to keep levels comfortably below clipping? Absolutely.
    Sure, if you record something conservatively (making best use of your analogue gear) it'll be more robust processing in that range, especially in floating point or double precision. HOWEVER. If you have pushed your recording levels into producing distortion on input at the analoge stage and then proceed to slam your levels ITB and within plugins that MAY or MAY NOT handle overs very well, you are putting yourself in a situation where the risk of compromised sound quality could become a reality.

    Rather negate that shit altogether by practicing conservative levels and just LISTENING. You'll save yourself hours of speculation, null tests, and fidelity paranoia and you'll be able to just get on with your work.

    Over and out.

    Cheers

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    Just to add, this is an interesting point:

    Quote Originally Posted by Thomas Lund
    The analog level of a sine wave at fs/6 (8 kHz when sampling at 48 kHz) can be up to 1.25 dB above the peak level in the digital domain, while at fs/4 the discrepancy can be up to 3 dB.
    Mull on that for a while.

    Cheers

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    Quote Originally Posted by Ethan Winer View Post
    Actually, that's another myth. I did a test a few months ago where I intentionally clipped a recording of an acoustic guitar in the digital domain by raising the level to be 2 dB above 0dBFS. Then I lowered the volume to match the original for a fair side by side comparison. Yes, it sounds slightly different from the original - not unlike slightly overdriving analog tape - but it's not horrible as some would have you believe. I'll be glad to share the file if anyone cares. Or, better, just do the same experiment yourself in any two-track audio editing program.
    Well, in this we have to disagree in terms of perception. I find even 2dB of digital clipping a fairly unpleasant sound but that's just my opinion. However, it's also worth saying that the effect gets worse rather rapidly as you go above your 2dB test point. In any case, I don't think anyone here is arguing that digital clipping is a "good thing" or that proper gain staging to ignore it shouldn't be one of the absolute basics of recording.

    Well, don't ignore that altogether because it's hugely important and relevant to this discussion. But I agree there's no need to record as close to zero as possible. I've been arguing that for years. Even with "only" 16 bits, the noise floor is 20-30 dB quieter than analog tape. So recording with peaks around -10 or even lower is fine. I object only when people claim that recording at -20 dB sounds "better" than recording closer to zero, because it doesn't. Unless gain-staging is wrong somewhere else in the chain. Recording at conservative levels is mainly for safety and convenience.
    I only disregarded 32 bit float operations for the sake of keeping the discussion in this thread simple. In my own "real world" I use a DAW that works natively in 32 bit float. In any case, that was just a detail--I fully agree that, as long as clipping is avoided, I can't hear a quality difference between -20 and -1. Actually, that's not quite true. If I have to apply significant gain to the -20 signal, I may well start to hear background noise (depending on what was used earlier in the chain).

    Absolutely. I work entirely ITB, so this doesn't affect me. But outboard gear doesn't enjoy the luxury of 32-bit floating point math, so levels in and out definitely matter.
    I'm in a slightly "hybrid" position on this. In my studio, I'm 100% ITB. However, much/most of what I do is sound for use in live theatre--so very often my mixes (even sometimes stems) are played back live which implies at least some analogue stages.



    Agreed, and I mentioned that earlier in this thread.



    Quote Originally Posted by Mo Facta View Post
    I disagree. The most compelling reason for lower levels is to keep the analogue components in the signal path from producing distortion on input and, in the digital domain, to prevent inter-sample distortion at the DA output. Clip point is not necessarily the point at which distortion will be produced. It may manifest many dB BELOW clip point, depending on the quality of the components.
    No disagreement that analogue levels are important. If, to satisfy a silly quest for your digital recordings to peak at some silly-high level you have to push the analogue input stages too high then clearly this is a bad thing. However, that's not the sort of situation I was referring to. At least on my set up I could achieve overly high digital levels without pushing my analogue stages at all. No, I obviously don't do that--but, for the sake of my previous post, I was assuming sensible gain staging throughout the system. Indeed, gain staging is something that I get pretty OCD about--it comes from far too many years in the broadcast industry where we were constantly aligning levels from source to destination via every intervening stage.


    I agree but what about the distortion that might have been introduced by using preamps with inferior components that introduce distortion at 6 or 9dB below clip point? That distortion will still be there no matter how much you turn it down and at 20 or 30 tracks, the cumulative effect will kill your recording. You'll no doubt get harmonic buildup somewhere in the spectrum no matter what your digital levels are.
    At the risk of sounding cavalier, if somebody has a pre amp so poorly made that this is an issue then they should save up for better. Reducing your digital levels to compensate for deficiencies in your analogue gear should be a stop gap only--it doesn't mean it's a good way of working in the long term. It's a bit like driving your car at 30 mph on the freeway because you know your brakes aren't good enough to do the speed limit. In any case, I was talking more about general principles than trying to compensate for every bit of defective or badly built gear.


    Exactly, so, if you don't have the time to null test every plugin (like most working engineers) the best thing to do is just keep your levels conservative and get on with the job which, of course, mostly entails LISTENING. It's amazing how the more listening experience you have, the less you need to know the results of a null test. Yes, they're interesting but for fuck sakes, who's got the time and the energy to test ALL of their plugins this way? How exactly will knowing the results make my mix any better? Did engineers of old refuse to work with an 1176 until they knew the results of a null test? Fuck that.
    I basically agree--but my conservatism starts earlier. I work with a relatively small range of hardware (and tend to have investigated the quality before I put it to actual production use) and an even smaller selection of plug ins--but that's just me. However, if I came across a plug in that started to sound bad with levels that should be "legal" I'd probably just stop using it rather than compensate for its shortcomings by adjusting all my levels downwards.

    In any case, we're getting to the stage of debating how many angels can fit on the head of a pin--or how many dB can fit in an audio file. In the "real world" I think most of us actually work in pretty similar manners and set levels in similar ways. The only thing I take real exception to is the assertion that ALL ELSE BEING EQUAL -20dBFS sounds better than -1dBFS. Yes, there are factors that can make this so and mitigate towards more conservative levels, especially when considering everything else in the chain. However, purely in the digital domain there should be no difference at all--and my experience of listening confirms this.
    That's what I do. I drink and I know things.
    -Tyrion Lannister (and Bobbsy)

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    Preamps are not the be all, end all of the analogue stage. There are numerous components in even a simple mic preamp that can cause distortion at many dB below clip point and I can GUARANTEE that many of the prosumer stuff out there utilizes these cheap inferior components. Distortion is not always immediately evident and can slip past when you're tracking so easily but when there's 20 to 30 tracks of the stuff, it builds up into something worse.

    Converter chips? Most of the time bad sound is not it's fault. It's the analogue crap they put before and after it that causes the distortion.

    ITB? Yes, a strict 0dBfs signal will sound the same as a lower signal on paper (heh) but when that signal hits the reconstruction stage there are many dangers if, 1. there are extraneous intersample peaks, and 2. the analogue components in the DA are not up to scratch. Sadly, this is the case for much of the entry to mid level stuff on the market. Many of these manufacturers use common chips like the Asahi Kasei stuff but cut corners and costs by skimping on the analogue stuff. THIS is the MAIN SOURCE of distortion. And then we have even crappier components to deal with in the consumer market in MP3 players and CDs. Read that Thomas Lund article. It's very informative on this topic.

    Cheers

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    What were we talking about....????

    I read both pages...I can't figure it out.



    I use analog a lot in my hybrid setup..preamps of course, but also track to tape, etc...
    When I dump into the DAW, you know, I never even bother to look at the interface/DAW input levels anymore.
    About the only thing I do is check to see if the A/D interface is set to +4 or -10, depending on which analog gear is feeding it signals.
    All my level settings are done in the front end analog stage, and those I do at the source and at the analog gear it's feeding, partially by analog meter and partially by sound/taste.

    When I then dump to DAW, sometimes the DAW levels end up in the -6 range, sometimes in the -18 range from track to track...I just let them fall where they may.
    I don't obsess about setting *DAW interface levels* to a specific range. I will NOT turn down or turn up a preamp just to hit a desired digital level. I let the analog front end do the work of setting proper levels.

    When I come back out of the DAW to mix OTB, I will trim my levels at the console as needed, as I may have changed digital levels somewhat while doing edits/comps/etc and while pre-mixing in the DAW, but it's never extreme, more just about balancing levels out between tracks, so when those levels come out of the DAW, they hit my analog OTB gear at about the same analog level as what I had at the front end.
    I don't much pay any attention to the DAW levels or obsess where they are hitting.

    Of course, for ITB mixing, the DAW levels are important when you start stringing the digital plugs together per track.

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