Basics of Gain Staging
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  1. #1
    Tech Mentor Halukar's Avatar
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    Default Basics of Gain Staging

    So I was reading through the thread about pros planning sets:
    http://www.djtechtools.com/forum/sho...t=23752&page=3, and noticed Mostapha brought up a really good point on a very rudimentary skill known as Gain Staging.

    This is something I see every day as an Audio Visual tech, but I realized that it may not be something that a ton of people know about. So here I will site some sources of information, rather than writing something less clear.

    http://www.inthemix.com.au/forum/sho...d.php?t=261462
    http://www.sweetwater.com/expert-cen...y/t--gainstage
    http://emusician.com/tutorials/max_headroom/


    Hope this helps!

  2. #2
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    Thanks ! /

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    Tech Guru Sherlock Ohms's Avatar
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    oooooh interesting.
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    Tech Mentor ponyboy's Avatar
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    Is gain staging why I need to ramp the volume up on my amp as it's a consumer piece of kit so has a gain stage of -10db compared to my pro gear having a gain stage of +4db?
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    Tech Guru sarasin's Avatar
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    Ahh cheers!

    Good info!
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  6. #6
    Tech Mentor Halukar's Avatar
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    Quote Originally Posted by ponyboy View Post
    Is gain staging why I need to ramp the volume up on my amp as it's a consumer piece of kit so has a gain stage of -10db compared to my pro gear having a gain stage of +4db?
    what type of amp is it? how many speakers are you running off of it and how many amps are the speakers rated for?

    *Edit: generally yes, the rest of your kit will not be drawing enough power for it to reach unity unless you crank that sucker up. It would probably be in your best interest to get one rated for the rest of your equipment, as having it cranked will probably fry it soon enough.
    Last edited by Halukar; 01-25-2011 at 12:51 PM.

  7. #7
    Tech Guru mostapha's Avatar
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    Quote Originally Posted by ponyboy View Post
    Is gain staging why I need to ramp the volume up on my amp as it's a consumer piece of kit so has a gain stage of -10db compared to my pro gear having a gain stage of +4db?
    No.

    Unless I'm missing something, you're talking about a home hi-fi amp that you're plugging your DJ mixer into. If you're using unbalanced RCAs to do that, your DJ mixer is probably staged for it's meter's 0dB reading to mean -10dBV. That part is probably right.

    The reason it's quiet is that consumer amplifiers are not as "overpowered" as pro gear. The "problem" is that if your speakers are probably rated for about 100W peak, 50W RMS, then your amp is rated the same, which is–deceptively–wrong.

    (don't worry about the numbers…they're arbitrary…specific numbers don't matter, just ratios and concepts)

    Using similar numbers, the "pro" amp matched to those speakers would be able to produce at least 200W peak and 100W RMS…because people who know how to set up sound systems know that those amps are never supposed to be turned up that loud…unless you can't afford it…which makes everything else more risky.

    The louder you have the volume on an amp set, the more noise it introduces…and the more likely it is for some uncontrolled transient to clip and sound horrible. The louder you have the amp set, the more likely it is that even a normal signal will be distorted.

    The funny thing is that one transient won't destroy speakers unless you're doing something really dumb. However, an amp that's turned up too loud and is constantly distorting will cause speakers to distort and wear early…if not causing some catastrophic damage at some point. It can also trip circuit breakers and cause the amp to wear/out or blow based mostly on heat production or overloading capacitors.

    Amateurs and consumers can't be expected to understand why they can't be expected to turn their volume control up over 5 when they want to go to 11, so most consumer-audio volume controls–however they're labeled–don't go to 100%. They go higher than 50% because it's expensive to overbuild something that much, but there's often some room left…still not a great idea.

    If you're using consumer audio for your amps/speakers, you know you (and everyone else) won't ever peak the DJ mixer over 0dB, you know how the power ratings work out, and you have some reassurance that the system isn't already worn out…go ahead and turn the hi-fi up, just leave some room at the top. If any of those aren't true…be safe and buy more powerful gear if you want it louder.

    I've damaged exactly one piece of audio equipment in my life…it was a friend's sony hi-fi amp. The owner bought it thinking exactly wrong…he bought a 100W (peak) amp to drive 100W (RMS) speakers, thinking it was safer this way…he wouldn't blow his speakers. Everything sounded like crap…the speaker cones were just too heavy for the amp to move them correctly, and in trying to get some dynamic range back, the owner had spent the last 2 years overdriving his amp and wondering why he had to set his high-eq so low…I didn't know about any of these issues at a house party and tried to make it sound right. I figured out what was going on about 5 seconds before the amp closed its eyes for good. He was right…the speakers were fine. Kinda. They played so many distorted highs, I don't think those tweeters will ever sound right.

    (side note: it was a house party, so i dealt with it by turning my RP5 'booth monitors' around to face everyone else…it was such a fun party, the owner decided it was worth buying a new amp to have fun for a night and learn how to not do it again)

    (more important side note: sony hi-fi amps have almost no headroom above the top of the master volume)

    That's why it's quiet.

    Where gain staging comes into play for most DJs is that it's never appropriate to hit the red. As far as -10dBV vs. +4dBV…that's mostly taken care of for you as long as you don't do something stupid like use an XLR to RCA adapter that isn't called a "DI Box". And if something like a hardware recording device of effects processor has a switch, make sure you're using the right one. Mostly, you can go by the cables as described in one of the linked articles.

    The more interesting part of this issue is gain staging inside Traktor.

    Traktor's gain staging is messed up. I have no idea why they made some of the design decisions they did.

    Like most other systems, Traktor appears to use floating-point math for internal mixing, summing, EQs, effects, and all that jazz. It's really hard to clip Traktor's internals. Unfortunately, it's really easy to clip your sound card outputs.

    DJing (with full tracks) in Live for over a year, I came to the practice of never letting my tracks peak above 0dB on the internal channel meters. How I did it is beyond the scope of this (already long) post, but the result was that most of my tracks had about a -4dB to -6dB gain setting attached to them. I did it that way so I could use a nice-sounding master limiter set for a couple dB of gain reduction at loud peaks without worrying about it actually squashing dynamic range very much.

    Traktor's auto gain sets most of my tracks to about +3dB. The values are right…they all sound very close in perceived volume. Unfortunately, the vast majority of my tracks clip my sound card output or kick in the limiter. Obviously, the answer is to use the limiter……except it's not. Traktor's limiter sounds like garbage to me, probably for no other reason than that it's likely giving me 15dB of gain reduction…instead of getting used to 1 or 2 in Live…which probably uses a better-quality plugin. I can't be sure what's causing it, because Traktor has no useful metering anywhere in the software except for the "clip" or "limiter on" lights…which I know do not account for inter-sample modulation distortion, so you can clip the output without those lights kicking in…I know…I've done it. It sounds bad. Actually, according to my tests, you get inter-sample modulation distortion even with the limiter, because it's just limiting the digital values to 0dB. Seriously…run Traktor's outputs into Live using soundflower or Jack or something…even with the limiter on, you'll clip Live's channel inputs if Traktor's master is anywhere near 0dB.

    The people who say to run Traktor's master a bit below 0dB are right, because Traktor's gain staging is just wrong.

    I honestly have no idea how to deal with it if you're using a controller. I mean…obviously, turn the master down. But then you're sending a cold signal to whatever's next. If it's a DJ or FOH mixer, just turn it up some…24-bit audio has more dynamic range than a lot of DJ and FOH mixers, so you're not losing much. If you're going into an amp, you're either going to be using Traktor's limiter, clipping your sound card, or overdriveing your amp (often by just a little).

    Just something to think about.

    In case anyone asks, no…I haven't tried any of this with anything but Traktor and Live. SSL and Deckadance don't have any worthwhile metering either, and I down't own any other software…so I haven't tried to figure out if they're as messed up as Traktor is.

    And, I'm really wondering how to use Traktor well with an old-school rotary mixer. I'd love to do that at some point if for no other reason than the fact that I like them, and I have no idea how to not lose dynamic range in the DJ mixer with Traktor at -14dB (like I run) without an input gain control…unless there's really like an extra 8 to 10dB at the top of the channel levels…that'd be fine.
    Last edited by mostapha; 01-25-2011 at 03:10 PM.

  8. #8
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    i found a fantastic tread on gain staging over on the Serato webstite. Thought you guys should take a read.

    http://serato.com/articles/scratchli...re-for-djs-101
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