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Levels and Gain staging Redux
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kelldammit
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I'm going to break this topic up into several posts. If one of the more advanced users wishes to tackle a relevant sub-topic, please feel free
These are just to help explain/clarify some of these things for the less experienced users among us.
Of course, everyone should feel free to chime in with additional suggestions, corrections, comments or questions!

1. Gain staging.
For a newcomer to recording, this is something you hear a lot of tirades, rants and general ballyhoo about.
It's important, and applies to pretty much every step of recording and mixing. But what exactly is it?
Basically, gain staging just means hitting your gear with signal at a level that said gear will perform its best at, while not destroying your signal in the process. It's the balance of maximizing signal strength without distortion, while minimizing the noise floor.

Step 1: Make sure you're using the right input to accommodate the previous device's output. If your gear is designed to operate at -10db, and you're hitting it at +4, it's probably not going to work at its best. Likewise, plugging a mic directly into a line input (or vice versa) won't get you optimal results.

Step 2: The best example of the second step is simply plugging a microphone into your audio interface's mic pre. Before you press the record button, you try to make sure you have strong signal from the mic, but aren't clipping, right? It's pretty intuitive. You almost automatically try to find the balance between not clipping if the signal gets loud, and not having too much noise from the pre because the level's too low. You want a clear, strong signal to work with, without too much noise or distortion. That's what it's all about, in a nutshell.

Where people seem to get confused is that this principle applies to EVERYTHING you put into the audio's path! To build on the mic/audio interface example, suppose you're using an external mic pre in between the mic and your interface. You'd first find the "sweet spot" between the mic and mic pre. Then you'd make sure you sent your mic pre's (line) outputs to the appropriate line inputs on the audio interface. Then you'd adjust the output of the pre, and the input of the interface to make sure you have strong signal, low noise, and no clipping. So if both devices are +4, and you set the output of the pre, and the input of the audio interface at unity gain*, you should be in the ballpark already, if not spot on.

While this seems obvious enough in the analog realm, does it apply to digital?
The short answer: yes, but generally for different reasons. You're usually not so much worried about noise floor with daw plugins. It becomes more an issue of headroom, which will be the topic of the next post.

kell

* Unity gain= the easiest way to explain unity would be on a mixer. If a channel is set to unity gain, it will output signal at the same level it receives it.

This message was edited 2 times. Last update was at 28/03/2012 20:23:22

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kelldammit
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Another one of those buzzwords we hear so much is Headroom.
So what is it, and why is it important?

It's actually a pretty simple concept. Headroom is the difference between its current level, and the point at which it will clip.
The nice thing about digital is that clipping occurs at 0dBFS (deciBels Full Scale). Since your meters read everything as a level below 0dbFS, the peak reading of a given track is basically the amount of headroom you have. If a track peaks at -10dbFS, you have 10 db of headroom.

Okay, well a 32 bit float engine gives us virtually unlimited headroom (1000+db), so why worry about it?
A good example that we've all probably run into would be this:
You've done your mix, and made sure that nothing's clipping, but yet when you export the mixdown file, a dialog box pops up and says "You're clipping! Please try again" (or language to that effect).
HUH?!?! What gives? How on earth can I possibly be clipping?!?

There are a couple of things that can cause this. A limiter on the master bus is an effective band-aid, but to actually cure the problem, you would want to pay closer attention to gain staging and headroom, both on the tracks themselves, and on the master bus. You need to leave some room for a bit of digital weirdness More specific examples of that later...

So how do you gain stage to allow adequate headroom in digital?
It's actually not as complicated as it might seem, but it does involve some care.
Per-track: Suppose you have a track that peaks at -10db. Now you put a compressor on that track. Very often, the auto-make-up gain will actually make the compressor's output hotter than the incoming signal was. The track might now peak at -6db or higher. All you'd need to do is adjust the makeup gain or the output level of the compressor so that what comes out is the same as what went in. This way, even after compression, you still have 10db of headroom. If you then add another effect after the compressor, you can be pretty sure you're not hitting it too hard, and thus aggravating any "digital weirdness" that THAT plugin might inflict. Be sure to make sure the output of each plugin is good prior to inserting the next one.
---[EDIT] You can also use the mixtool plugin or something like sonalksys' FreeG if the plugin itself doesn't have an output gain or meter. Simply insert mixtool or FreeG after the plugin, and reduce gain until your track meter shows the desired level. Pay extra close attention to Dynamics processors and EQ's in particular. Fortunately, the presonus comp and pro eq both have output levels built-in, so they save you some trouble [/EDIT]---

Mix Bus: Treat the master bus as you would any other track. Leave some headroom (especially if you're going to put an eq on there)...don't just aim for 0db. If you want it louder while mixing, turn up your monitors! You can always use a limiter when you export if you want a "hotter" file, or better yet, save that part for the mastering process.

The overall benefit of good gain staging is that you never put yourself in a position where you're out of headroom, be it on a channel, or on the mix bus. It makes it much easier to maintain a clear, dynamic result. Mix bus headroom is a part of what the K-metering system helps address, by calibrating and metering in such a way as to automatically ensure adequate headroom. More on that later, if folks are interested.

So, how much headroom is "enough"? I think I feel another post coming on....

k

This message was edited 4 times. Last update was at 28/03/2012 23:36:25

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CTStump
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This is a great idea my friend, will try to add and bump to help keep this tread up so this info can stay up for perusal and input.
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LMike
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As an actual working matter, I agree with all of it, 100%. As a purely ... technical ... matter... I know that a lot of it doesn't actually matter. I also know that putting that idea forward leads to places that aren't so good for the net, and besides, I practice gain staging pretty much the same way most others describe here, leaving plenty of headroom along the way.

The only time it really comes into play for my preferences is handling other people's tracks. Then I do what Johnnie talks about, trim things down to a level more in line to the levels I actually record at. Nothing I actually personally record ever has to be trimmed that way though.

Anyway, I just like to occasionally remind people that 32-bit float really changed - everything - and that (as a purely technical matter) none of it changes the sound (or diminishes headroom) - between the I/O hardware - in any way at all. I've tested it all... even with the master bus at -80... no difference at all... complete null.

But ... good gain staging in the way being described here and elsewhere is very good practice anyway so I agree with the methodology of it all as being a very good practice to adhere to.

This message was edited 3 times. Last update was at 28/03/2012 23:58:23

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CTStump
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LMike wrote:As an actual working matter, I agree with all of it, 100%. As a purely ... technical ... matter... I know that a lot of it doesn't actually matter. I also know that putting that idea forward leads to places that aren't so good for the net, and besides, I practice gain staging pretty much the same way most others describe here, leaving plenty of headroom along the way.

The only time it really comes into play for my preferences is handling other people's tracks. Then I do what Johnnie talks about, trim things down to a level more in line to the levels I actually record at. Nothing I actually personally record ever has to be trimmed that way though.

Anyway, I just like to occasionally remind people that 32-bit float really changed - everything - and that (as a purely technical matter) none of it changes the sound - between the I/O hardware - in any way at all. I've tested it all... even with the master bus at -80... no difference at all... complete null.

But ... good gain staging in the way being described here and elsewhere is very good practice anyway so I agree with the methodology of it all as being a very good practice to adhere to.


Have to agree somewhat, as there is no problem when the signal to noise ratio (SNR) pushes the noise floor way down in the case of 24bit audio (aprox. -124db) as with digital rather than tape (aprox.-40db) where the noise floor is a lot higher and headroom is critical, it's not so much for digital Daws these days my friend.

This message was edited 4 times. Last update was at 29/03/2012 07:15:38

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zentatonic
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Excellent thread Kell. Thanks for taking the time to write this stuff out. It's definitely for the good of the community.
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LMike
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@CTStump:

It's really (all the really great working advice here in this thread notwithstanding) one of the, if not the, most commonly misunderstood things in digital.

Headroom is near infinite in 32-bit. Nothing changes but amplitude and we change amplitude of various signals in a multitude of ways all through an audio project, at multiple stages. 24-bit plugs aside (which we shouldn't be using), you simply cannot run out of "internal" headroom (between the I/O hardware) without stacking more gain stages on a channel than you'll ever actually use, and the master bus fader is just another simple gain stage, one of many, it doesn't change the sound in any way at all, no matter what level is coming into it.

It's a very hard concept to accept - because it just doesn't "look" right - until you test it with really, really insane track levels and see that it all sounds exactly the same. Most of the good advice being passed down on Gearslutz and similar from some great mix engineers related to that actually came from PT, and it was (and still is) much more relevant on those systems.

There are valid reasons to stage but headroom isn't one of them, not in 32-bit float. You kinda can't ever run out of headroom, ever. The headroom we talk about is "visual" (metering a 24-bit scale), not actual... until hardware comes into play... and then... compliance becomes a simple matter of amplitude.

Anyway, great thread. Thanks Kell.

This message was edited 4 times. Last update was at 29/03/2012 00:59:12

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CTStump
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LMike wrote:@CTStump:

It's really (all the really great working advice here in this thread notwithstanding) one of the, if not the, most commonly misunderstood things in digital.

Headroom is near infinite in 32-bit. Nothing changes but amplitude and we change amplitude of various signals in a multitude of ways all through an audio project, at multiple stages. 24-bit plugs aside (which we shouldn't be using), you simply cannot run out of "internal" headroom (between the I/O hardware) without stacking more gain stages on a channel than you'll ever actually use, and the master bus fader is just another simple gain stage, one of many, it doesn't change the sound in any way at all, no matter what level is coming into it.

It's a very hard concept to accept - because it just doesn't "look" right - until you test it with really, really insane track levels and see that it all sounds exactly the same. Most of the good advice being passed down on Gearslutz and similar from some great mix engineers related to that actually came from PT, and it was (and still is) much more relevant on those systems.

There are valid reasons to stage but headroom isn't one of them, not in 32-bit float. You kinda can't ever run out of headroom, ever.

Anyway, great thread. Thanks Kell.


Mixing is more philosophy then technical in my opinion it's what you find that works for you, it also helps to have a working knowledge as a basis which I believe this thread will provide with and without debate. I can always learn something new to add to the toolbox and this thread is a good thing to keep going as we all evolve in our pursuit of the sound we are after my friend. Kudos to Kell and keep it up.
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LMike
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For sure. My comments weren't meant to debate anything or anyone. I just added my viewpoint to the collective.

Thanks CT.
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LMike wrote:For sure. My comments weren't meant to debate anything or anyone. I just added my viewpoint to the collective.

Thanks CT.


No problem my friend I always get something from opposing point's of view's not implying your argumentative ( I secretly love argument's too, psssst... don't tell anybody).
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kelldammit
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LMike wrote:As an actual working matter, I agree with all of it, 100%. As a purely ... technical ... matter... I know that a lot of it doesn't actually matter. I also know that putting that idea forward leads to places that aren't so good for the net, <snip>

Exactly. I just like trying to make a reasonable argument for good practice, that at least shows some "method to the madness", however technically relevant it may or may not be these days I know from the rest of your post that you totally get the gist.

and besides, I practice gain staging pretty much the same way most others describe here, leaving plenty of headroom along the way.
The only time it really comes into play for my preferences is handling other people's tracks. Then I do what Johnnie talks about, trim things down to a level more in line to the levels I actually record at. Nothing I actually personally record ever has to be trimmed that way though.

That's an excellent point, and it serves to illustrate the importance of paying attention to gain staging right from the start. Johnny showed a good example of how to deal with the less ideal scenario we're all bound to run into at some point.

Anyway, I just like to occasionally remind people that 32-bit float really changed - everything - and that (as a purely technical matter) none of it changes the sound (or diminishes headroom) - between the I/O hardware - in any way at all. I've tested it all... even with the master bus at -80... no difference at all... complete null.

Yup, and most audio i/o can't even reproduce a full 24 bits of audio, even! So it's largely mathematical nitpicking, versus any real practical difference (unlike, say...the difference between 16 and 20 or 24 bit). That said, i sort of think that the idea of "virtually unlimited headroom" in 32-bit float tends to undermine the importance of good gain staging and level practices in the minds of many, generally speaking. Of course, if you're already doing it right, it's going to make even less of a completely negligible difference

But ... good gain staging in the way being described here and elsewhere is very good practice anyway so I agree with the methodology of it all as being a very good practice to adhere to.

Thanks for the thoughtful comments, Mike. I'm glad you chimed in here. Now, where do i send the check?

k

This message was edited 1 time. Last update was at 29/03/2012 01:10:39

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kelldammit
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LMike wrote:@CTStump:
There are valid reasons to stage but headroom isn't one of them, not in 32-bit float. You kinda can't ever run out of headroom, ever. The headroom we talk about is "visual" (metering a 24-bit scale), not actual... until hardware comes into play... and then... compliance becomes a simple matter of amplitude.


Good point about hardware.

Also, for the newer folk: a couple of "back in the day" examples of how the usual headroom recommendations and guidelines came to be so well-established in the first place (as regards digital).

1. Mike made a great point about older versions of PT (their hardware didn't use floating point for its mix bus, so you had a definite limit to the headroom).
2. Another is that we largely operated with 24 bit files (and still do), and DAWs would often render bounces to the bit depth of the original file. So, if you and gained up a track, and effected the hell out of it in your daw, it wouldn't clip in the 32 float mixer. But once you BOUNCED it, the DAW would usually bounce it back to the source format (i.e. 24 bit), in which case, you got a nasty clipped-to-oblivion bounce file. I seem to remember that DP's track clip meters would actually trigger at the 24 bit mark to warn you of that specific danger! Old old versions of cubase used to behave this way as well. This is referring to ctrl+b style bounces, not renders through the master channel.

PreSonus skirts that issue, as Studio One renders bounces at 32float, regardless of the source file and project setting's bit depth. I'd expect most other daws to behave similarly nowadays.

Tomorrow, hopefully we'll go into levels (as Mike touched on with his comments earlier).

Now get off my lawn!

This message was edited 3 times. Last update was at 29/03/2012 02:43:24

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JayPhil
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Quick question Kell,

I understand the concept of the 32bit float. My question is, do you think that I would benefit in setting my songs
to 32bit from the get go, or just leave the files @ 24bit.


Thanks

JayPhil
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JayPhil wrote:Quick question Kell,

I understand the concept of the 32bit float. My question is, do you think that I would benefit in setting my songs
to 32bit from the get go, or just leave the files @ 24bit.


Thanks

JayPhil


the internal engine is 32bit (64bit if you check the box in the options panel), I always run 24bit,48knz with no problem my friend, Kell will get to you soon with his take.

This message was edited 1 time. Last update was at 29/03/2012 07:20:37

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Great idea Kell!! Wish we could combine this with the livestreams.....lol.

But as soon as I post the video snips from the broadcast, maybe you can interweave them with your post.!!

Oh, and thanx for the help with the Livestreams.

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