Headroom in digital audio

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Re: Headroom in digital audio

Postby macrae11 » Tue Jan 10, 2012 1:48 pm

Mathieu Benoit wrote:
macrae11 wrote:All that being said, I would never go to this much trouble for a drum sub headroom issue. Usually drum sub routing is a bit simpler than a full mix(though not always) so I'll just bring all the faders down. The way I do this is with a VCA track assigned to the drum group. This way I have full control of levels both going into my drum sub and it's processing(VCA) and overall drum sub level post processing(drum sub AUX).


Ah VCA tracks... Right. Forgot about that, I've yet to use them. I simply bring down the faders of the channels in that subgroup for now if I need to.

Yeah the nice thing about VCA tracks though is you can still manipulate the individual relative mix levels while still having master control.
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Re: Headroom in digital audio

Postby Mathieu Benoit » Tue Jan 10, 2012 1:52 pm

macrae11 wrote:You've sort of got it, but the picture analogies are throwing you off. First of all bit depth refers to dynamic range, not "quality", or resolution. Since all digital files have the same max level of 0dBFS, you don't actually gain any headroom when increasing bit depth, you actually gain footroom. But since we have more footroom before the noise floor, we can record at a lower level, thereby allowing ourselves more headroom, which is what this conversation is all about. 24 bit actually has 144dB of dynamic range which is approximately the range from dead silence to making your eardrums meet in the middle of your head. ie Way more than you need. But this allows us lots of freedom with levels, as long as we stay clear of 0.

Another misconception is that 32 bit will sound better than 24 bit which is totally false. 32 bit files are capable of a much greater dynamic range, but as stated 24 bit has more than enough dynamic range for humans, so as long as you maintain good gain structure and stay within that range there will be no difference between the 24 bit and 32 bit float files. If you do stray outside that range in 32 bit float, when you reduce down to 24 bit, you will be in for a world of hurt. 32 bit float files are actually just 24 bit files with an 8 bit modifier to fake their extended dynamic range. So basically you still only have 144 dB of dynamic range, but that range can be from 0-144, or 96-240, 144-288, or 576,254-576,398.

Everything above 24 bit is not float, for instance Pro Tools HD has a 48 bit fixed internal mixer, so it has a true dynamic range of 288dB, which is only useful when we starting getting into the math of signal processing, which I'm am woefully unprepared to discuss at any length. All of this is before we start talking about dither too, which is a whole nother kettle o' fish.


Quoted for emphasis. This post gets to the heart of the technical matter at hand better than I could ever have explained it.
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Re: Headroom in digital audio

Postby Malcolm Boyce » Tue Jan 10, 2012 1:55 pm

macrae11 wrote:
Malcolm Boyce wrote:This is truly one of the best things in Sonar is the flexibility in routing. There is no difference between any of the busses or groups or auxes... and any of their main outs are assignable to any physical hardware output.

Pro Tools is the same way, it just has tracks/channels with different functions, but the routing is the same in all tracks and can go anywhere. In fact they're all just called buses, Matt and I are just referring to them by their function as opposed to what they are.

But is there a mix buss that is always the Master, and is it different from any other mix buss?
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Re: Headroom in digital audio

Postby Mathieu Benoit » Tue Jan 10, 2012 2:01 pm

Malcolm Boyce wrote:But is there a mix buss that is always the Master, and is it different from any other mix buss?


I'll try to answer this. In Pro Tools the "mix buss" is always there under the hood. The stereo master fader that you associate with that can be created but signal still goes to the physical output selected on each individual channel regardless of if you have a "master fader" create for that buss or not. Cubase works different as there is a dedicated "master mix buss/fader" much as I'm assuming as there is in Sonar.

Malcolm Boyce wrote:This is truly one of the best things in Sonar is the flexibility in routing. There is no difference between any of the busses or groups or auxes... and any of their main outs are assignable to any physical hardware output.

There are no "main outs" so-to-speak in Pro Tools though. You assign every individual channel to whatever physical output or virtual buss that you want. You can choose to create a master fader dedicated to that buss but it's not necessary.

I've seen Andrew do some incredibly complex routing schemes in Pro Tools to facilitate recall of sessions through stems when he uses a lot of outboard gear, and I can't imagine being able to pull it off in Cubase.
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Re: Headroom in digital audio

Postby Mathieu Benoit » Tue Jan 10, 2012 2:09 pm

Malcolm Boyce wrote:Image


Hmmm.... the DBFS scale in Sonar looks to be linear. That hurts my head.
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Re: Headroom in digital audio

Postby macrae11 » Tue Jan 10, 2012 2:10 pm

Yeah Matt got it. Just to clarify master faders are "under the hood" for every bus and IO. So they are part of the mixer and so take up no more DSP, or eat up your track count because they are inherently there. If you want to manipulate it, you need to create a master fader track and assign it to your bus/IO.

So there is no fader permanently assigned to your main 1-2 outs, and if you do assign a master fader to your 1-2 outs, it is no different than any other master fader on any other bus or IO. I assume this is because there's not really a "standard" way anyone sets up, so you can customize your own templates to your individual needs.
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Re: Headroom in digital audio

Postby macrae11 » Tue Jan 10, 2012 2:11 pm

Mathieu Benoit wrote:Hmmm.... the DBFS scale in Sonar looks to be linear. That hurts my head.

Yeah and it still only appears to go to 0dBFS. How do you see if it's going to +6dBFS like you mentioned?
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Re: Headroom in digital audio

Postby Malcolm Boyce » Tue Jan 10, 2012 2:13 pm

Mathieu Benoit wrote:Cubase works different as there is a dedicated "master mix buss/fader" much as I'm assuming as there is in Sonar.
Yeah... No. That's what I'm trying to get clear in my head. In Sonar, there is no dedicated "master" buss, that functions as a master. You can send the main out of a track/channel to any buss or physical out of the system directly.

I guess it's just a different way of routing that until you see it in front of you, it's hard to grasp.
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Re: Headroom in digital audio

Postby Christian LeBlanc » Tue Jan 10, 2012 2:15 pm

macrae11 wrote:Yeah and it still only appears to go to 0dBFS. How do you see if it's going to +6dBFS like you mentioned?

Would it just show up numerically as peaks?
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Re: Headroom in digital audio

Postby Malcolm Boyce » Tue Jan 10, 2012 2:18 pm

macrae11 wrote:
Mathieu Benoit wrote:Hmmm.... the DBFS scale in Sonar looks to be linear. That hurts my head.

Yeah and it still only appears to go to 0dBFS. How do you see if it's going to +6dBFS like you mentioned?
The meter tops at zero, but the peak level is recorded as a separate display each time you roll audio.

I can't remember all the parameters you can change as far as the meter display goes. I know it's customizable to a point. The images I'm uploading are from my lappy setup, which isn't my main rig, so things probably even look different between the two... :-)
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Re: Headroom in digital audio

Postby Malcolm Boyce » Tue Jan 10, 2012 2:19 pm

Christian LeBlanc wrote:
macrae11 wrote:Yeah and it still only appears to go to 0dBFS. How do you see if it's going to +6dBFS like you mentioned?

Would it just show up numerically as peaks?
Exactly.... It's a separate numeric display.
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Re: Headroom in digital audio

Postby Mathieu Benoit » Tue Jan 10, 2012 2:54 pm

Malcolm Boyce wrote:In Sonar on a buss there is "Input Gain" control at the top which is handy if you are processing on the mix and want to control the overall level of what's coming in as opposed to the output of the buss.

Can you control the "input gain" only on a buss or on any type of channel? In Pro Tools you can add a "trim" plugin as an insert on any channel to adjust the PFL since the inserts are all prefader (except for Master Channels.) However there is no built in "trim" control in Pro Tools per se. I found it strange to begin with since Cubase had dedicated input channels that you could adjust the imput gain for, but now that I look back... the entire structure of how Cubase works is incredibly not intuitive. However input gain control for each channel would make sense wouldn't it? That being said, I don't find myself missing it either...
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Re: Headroom in digital audio

Postby Mathieu Benoit » Tue Jan 10, 2012 3:03 pm

I'm looking again at your mixer image for Sonar... What's up with the divisions of the channels? It reminds me of Cubase where there is a dedicated input section, mixer section and output section.
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Re: Headroom in digital audio

Postby Malcolm Boyce » Tue Jan 10, 2012 4:32 pm

Mathieu Benoit wrote:I'm looking again at your mixer image for Sonar... What's up with the divisions of the channels? It reminds me of Cubase where there is a dedicated input section, mixer section and output section.
Yes. In the mixer window it's tracks, masters, and outputs. You can select which you want to be looking at, in any combination.
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Re: Headroom in digital audio

Postby Mathieu Benoit » Tue Jan 10, 2012 4:41 pm

Malcolm Boyce wrote:
Mathieu Benoit wrote:I'm looking again at your mixer image for Sonar... What's up with the divisions of the channels? It reminds me of Cubase where there is a dedicated input section, mixer section and output section.
Yes. In the mixer window it's tracks, masters, and outputs. You can select which you want to be looking at, in any combination.


I like the fact that Pro Tools is basically a blank slate. I never used to like it though, because I couldn't wrap my head around the fact that there wasn't a concrete "output" section.
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Re: Headroom in digital audio

Postby Mathieu Benoit » Tue Feb 28, 2012 10:54 am

Mathieu Benoit wrote:An engineer just sent me some guitar tracks for a client I'm doing vocals for this weekend. Peak? 0dbfs. Average: -3dbfs facepalm


It wasn't a deal breaker, but you heard it for yourself Andrew.
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Re: Headroom in digital audio

Postby macrae11 » Tue Feb 28, 2012 11:53 am

Oh that's what you were referring to. Yeah I noticed it tiny bit in the mix, but nothing that I'd lose sleep over. Very obvious solo'd though.
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Re: Headroom in digital audio

Postby Mathieu Benoit » Tue Feb 28, 2012 12:08 pm

macrae11 wrote:Oh that's what you were referring to. Yeah I noticed it tiny bit in the mix, but nothing that I'd lose sleep over. Very obvious solo'd though.


Exactly. In the mix it never jumped out at me as being too terribly obvious and since I didn't track it.... *dusts hands*
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