Gain Structure | FOH Masterclass ft Robert Scovill | Hillsong Creative Audio Training

Summary

The speaker emphasizes the critical role of gain structure in digital audio, particularly in live sound engineering. They argue for a single optimal method to set input gain on digital consoles to ensure the console operates at its best. Explaining the non-linearity of faders and the importance of high-resolution mixing, the speaker details why setting input gain correctly is essential for maintaining bit resolution and avoiding noise. They contrast live sound with studio recording, highlighting the unique challenges of live mixing and the impact of input gain on fader levels, dynamics processing, and recording levels. The talk concludes with advice on using audio subgroups effectively to balance levels without sacrificing audio quality.

Takeaways

• 🔊 Gain structure is critical in digital audio to ensure optimal console operation and prevent distortion.
• 🎛️ Setting input gain correctly is fundamental; it simplifies subsequent mixing and mastering processes.
• ⚖️ Faders in a console are not linear; moving a fader represents a logarithmic, not linear, change in volume.
• 📈 The position of faders is crucial for high-resolution mixing, aiming to keep them in the upper range for better control.
• 🎚️ Input gain on a digital console should be set to achieve a level around zero dB, aligning with line level standards.
• 📊 Different console scales like dBu, dBr, and dbFS represent the same signal level but in different ways.
• 💾 In live sound, a 24-bit depth preamp translates to approximately 6 dB per bit, maximizing bit resolution for clarity.
• 🔉 High input levels in live sound can indicate the need for a more powerful PA system rather than adjusting console levels.
• 🔕 Turning down the preamp to manage loud signals can result in lower bit rates and reduced resolution, affecting sound quality.
• 🔄 Using audio subgroups (sub masters) instead of VCAs preserves gain potential for aux buses and maintains optimized levels for effects processing.

Q & A

Why is gain structure important in digital audio?

Gain structure is crucial in digital audio because it ensures the console operates in an optimized way. If the gain is not set correctly, it can lead to poor sound quality and loss of resolution, which is especially problematic in digital audio where there is no room for forgiveness as there might be in analog.

What is the recommended way to set input gain on a digital console?

The recommended way to set input gain on a digital console is to adjust the preamp until the signal reaches zero on the line level, which translates to around +4 dBu in analog terms. This ensures high-resolution mixing and optimal operation of the console.

Why is it not advisable to skip setting input gain correctly?

Skipping the correct setting of input gain can lead to a signal that is either too high or too low. A signal that is too high can clip, leading to distortion, while a signal that is too low can result in noise and a loss of bit resolution, negatively impacting the overall sound quality.

How does the position of a fader affect the change in volume?

The position of a fader on a console is not linear but logarithmic. This means that moving the fader a certain distance at a higher level results in a larger change in volume than the same distance at a lower level. It's important to have faders in a high-resolution position, typically around zero, for optimal mixing.

What is the purpose of a preamp in a sound console?

A preamp is used to amplify a mic level signal up to line level. This is necessary because all consoles are optimized to work at line level, not mic level. The preamp ensures the signal is strong enough to be processed effectively through the console.

What is the significance of the line level in a console?

Line level in a console is a reference point that indicates where the signal should be for optimal performance. In the context of the script, line level is represented by zero on the console's meter, which corresponds to +4 dBu in analog, ensuring the console is set up for high-resolution mixing.

How does the bit depth of a digital signal affect the noise level?

In digital audio, bit depth determines the dynamic range and the signal-to-noise ratio. A higher bit depth, such as 24-bit, provides a greater dynamic range and better signal-to-noise ratio, meaning the noise is less likely to compete with the main signal. This is important for maintaining audio quality.

What is the relationship between input gain and fader levels in live sound?

In live sound, the input gain directly affects the fader levels. If the input gain is set correctly, the fader can be positioned for high-resolution mixing. If the input gain is too high or too low, it can force the fader levels to be adjusted in a way that compromises the audio quality or the dynamic range of the mix.

Why is it important to set the input gain to maximize the bit resolution for live sound?

Maximizing bit resolution in live sound ensures that the main signal is represented with the highest possible clarity and detail. This is important because live sound engineers often have to manage a variety of signals with different levels, and maximizing bit resolution helps to maintain audio quality across the board.

What is the difference between using a VCA subgroup and an audio subgroup in live sound?

A VCA subgroup adjusts the gain of all channels in the subgroup uniformly, which can reduce the bit resolution and affect the dynamics processing and aux levels. An audio subgroup, on the other hand, allows for independent level control of the subgroup without affecting the individual channel gains, maintaining optimal levels for recording and processing.

Outlines

00:00

🎛️ Setting Input Gain on Digital Consoles

The speaker emphasizes the importance of understanding gain structure in digital audio, especially when setting input gain on a digital console. They argue that getting the input gain right is crucial for optimal console operation. The speaker contrasts digital audio with analog, noting that digital audio is less forgiving, and analog has more flexibility. They explain that the goal is to set the input gain so that the faders can operate in a high-resolution area, which is akin to having a lot of headroom. The speaker also discusses the non-linear nature of faders, explaining that the change in dB increases as the fader position goes lower. They stress the importance of setting the input gain correctly to avoid issues with PA systems and to ensure high-resolution mixing.

05:01

📊 Understanding Line Level and Input Gain

The speaker delves into the concept of line level and why it's essential to set input gain to achieve it. They explain that a preamp is necessary to amplify mic-level signals to line level, which is critical because consoles are optimized to work at line level. The speaker clarifies that line level corresponds to +4 dBu in analog terms and -20 dBFS in digital terms. They discuss the importance of achieving line level for optimal signal-to-noise ratio in analog and bit depth in digital. The speaker also highlights the difference between live sound and recording engineering, emphasizing that in live sound, the goal is to have the main signal at line level to maximize bit resolution and minimize background noise interference.

10:02

🎚️ Maximizing Resolution in Live Sound

The speaker discusses the challenges of live sound engineering, particularly the need to balance fader levels and recording levels. They explain that if a signal, such as a bass drum, is too loud for the room, it indicates a need for a more powerful PA system. The speaker warns against turning down the preamp to adjust levels, as this results in lower bit rate and resolution. They also discuss the impact of level adjustments on aux levels and effects processing, emphasizing that optimizing the console for line level is crucial for maintaining high-resolution recording and effective dynamics processing.

15:04

🔊 Balancing Levels for Live Sound and Recording

The speaker addresses the issue of setting appropriate levels for live sound and recording simultaneously. They explain that turning down a signal to fit the room's acoustics can negatively impact recording levels and dynamics processing. The speaker suggests using audio subgroups, or sub masters, to set levels for different elements of a mix, such as drums or guitars, without affecting the optimized line level. They caution against using VCA subgroups for this purpose, as it can reduce gain potential for aux buses and complicate dynamics processing. The speaker concludes by reiterating the importance of setting input gain to line level for optimal console performance in live sound applications.

Keywords

💡Gain Structure

Gain structure refers to the arrangement of gain levels throughout an audio signal path. In the video, it is emphasized as a critical aspect of digital audio, ensuring that the signal levels are optimized for the best possible sound quality. The speaker is on a mission to educate about the importance of proper gain structure to prevent the system from getting 'out of whack', which can lead to a non-forgiving digital environment where mistakes are more apparent.

💡Input Gain

Input gain is the level at which the initial audio signal is set before it enters the mixing console. The video discusses the simplicity yet paramount importance of setting the correct input gain on a digital console. Correctly setting input gain ensures the rest of the audio processing is easier and more effective, as it is the foundational step in managing audio levels.

💡Faders

Faders are the sliding controls on a mixing console used to adjust the volume of an audio signal. The video explains that faders are not linear but logarithmic, meaning a small movement at a higher fader position results in a larger volume change. The speaker stresses the importance of having faders in a high-resolution position for precise mixing, which is particularly important in live sound engineering.

💡Line Level

Line level is a standard signal level used in audio equipment, typically around +4 dBu. The video discusses the necessity of getting mic level signals to line level because all consoles are optimized to work at this level. The speaker explains that setting the input gain to achieve line level is essential for proper signal transport through the console.

💡Bit Depth

Bit depth refers to the number of bits of information in a digital audio signal, which affects the dynamic range and quality of the audio. In the video, the speaker talks about the importance of having enough bit depth to avoid turning the signal into noise, especially in digital audio where bit depth directly translates to the resolution of the audio signal.

💡Signal-to-Noise Ratio

The signal-to-noise ratio (SNR) is the level of a desired signal compared to the level of background noise. The video touches on the concept that in digital audio, the concern shifts from analog signal noise to bit depth and how it affects the SNR. The speaker emphasizes that proper input gain is crucial for maintaining a high SNR and thus, a cleaner audio signal.

💡Audio Subgroup

An audio subgroup, also referred to as a sub master in the video, is a way to control multiple audio channels from one fader. The speaker explains that using an audio subgroup allows for maintaining optimized levels at the console while adjusting the overall level of a group of instruments or vocals in the mix, without affecting the individual channel levels or recording levels.

💡VCA

A VCA, or Voltage-Controlled Amplifier, is a type of fader that controls the gain of multiple channels simultaneously. The video discusses the difference between using a VCA and an audio subgroup. The speaker cautions against using VCAs to set levels in the room, as it can lead to loss of gain potential and affect dynamics processing, whereas an audio subgroup preserves these aspects.

💡Dynamics Processing

Dynamics processing encompasses techniques like compression and limiting, used to control the dynamic range of an audio signal. The video mentions that when input gain is set correctly, the console is optimized for dynamics processing, allowing for more effective use of gates, compressors, and other processors.

💡Headroom

Headroom in audio is the amount of space between the current level of an audio signal and the maximum level before distortion occurs. The video script discusses the concept of headroom in relation to live sound, indicating that if a signal is too loud for the room, it suggests the need for a more powerful PA system rather than adjusting levels within the console.

Highlights

Gain structure is crucial for optimizing digital console performance.

Digital audio is less forgiving than analog, making correct gain setting essential.

The importance of setting input gain correctly on a digital console.

Faders are not linear; their movement represents a logarithmic change in volume.

The goal is to mix in high resolution with faders in the upper range.

Live sound engineers face unique challenges not present in recording or post-production.

Consoles are optimized to work at line level, not mic level.

Preamps are necessary to convert mic level signals to line level.

Line level is indicated by a meter, typically at -10 or -20 dB.

Input gain should be set so that the signal is at line level for optimal performance.

Signal-to-noise ratio is less of a concern in digital audio due to the absence of analog noise.

Bit depth is a critical factor in digital audio quality.

24-bit depth provides 6 dB of headroom per bit, maximizing resolution.

In live sound, it's important to keep the main signal strong relative to background noise.

Turning down the preamp to manage loud signals can reduce bit rate and resolution.

Using a VCA to control room levels can affect the gain potential for aux buses.

Audio subgroups, not VCAs, should be used to set levels for drums, guitars, and other groups.

Optimizing input gain is key for effects processing, such as noise gates and compressors.

The relationship between console gain, PA system size, and live sound balance.

Transcripts

so uh one of the things i want to talk

to you guys about though and i'm kind of

on a little bit of a mission

um

to go out and make sure everybody kind

of understands this

because gain structure is such an

important aspect of digital

uh and to try to help you kind of get

things back together on your console and

make sure it's actually operating in a

very optimized way for you okay because

you get out of whack really easily in

digital

and it's not too forgiving you know in

analog it's a little more forgiving but

in digital it is not so i want to talk

to you about how to set input gain

something as simple as setting input

gain

on a digital console because once you

get that part right the rest of it just

becomes so so easy

but we kind of have a tendency to just

skip over this first step and

you know

i mean in analog we can say you know

there's probably a couple of different

philosophies on how to set analog input

gain we can make cases for different

ways to do it

i know this is going to rub you the

wrong way but i'm going to say it

there's one way

to set input game for a digital console

it's one way

anything else i can i can argue you

right out of it

okay so let's talk about it you okay

with that yeah okay

so this has to do

with

and and i'll preface this part of it by

saying you know live sound engineers

have some really really unique

challenges we have challenges that

recording engineers don't have we have

challenges that post engineers don't

have and a lot of it revolves around

getting our console optimized to both

kind of tracking and mixing workflows we

got to do both those things at the same

time

right and a lot of it is built around

fader position

okay here's the important part to

remember faders are not linear right

meaning if i if the fader is sitting up

in this area and i move it this distance

that represents 6 db of change right if

i go down in the scale now notice the

distance has decreased but the amount of

change has increased

and if i go down even farther this very

small change represents really really

big change right it's not linear

right it's logarithmic as a matter of

fact so the idea is that we want to be

able to mix

mix in high resolution we want to have

faders sitting up in this position now

i'm not here to say it has to sit at

zero for my money if it sits

plus 10 minus 10 you're in high

resolution

okay but down here you got issues

you know especially with the pa systems

that are out there today i mean you can

make small changes and hear small

changes

okay i mean it's very analogous to

mixing in a high resolution studio all

right so our goal is to get our console

in a set up in a way where we can mix in

high resolution okay you're buying it so

far

okay

so let's talk about uh input gain

concepts this is where the arguments all

start all right so we're going to build

a very very simple circuit here

we're going to have a preamp and

we're going to have a meter

all right so

here's where we start the question

why do we have a preamp

anybody want to take a stab at it why do

we need a preamp

to amplify the signal why do we need to

amplify the signal

because the signal's low

why is the signal low being a problem

because i'm telling you right now when

you can answer this question you're 99

of the way there yeah

that's part of it that's coming but

let's let's just stay in analog for a

second why do i need a preamp

well that's true

but it's not the reason why

we need a preamp to be able to take a

mic level signal to line level

period

end of story

now let's let's just push away all the

godzilla's the concepts of well some

preamps sound better than others and all

that that doesn't deal with the why

the why we need a preamp is i need to

get mic level signals

to line level

okay why do we need to do that

yeah well that's that's true

but there's an actual i mean just

flat out reason that we need to do it

because all consoles are optimized

underneath the hood to work at line

level not mic level

okay

so

where's line level how do we know where

line level is

anybody

minus 15 zero which is it you pick one

that's true okay so the the answer to

what he's getting to there is we have a

meter to tell us

we have a meter to tell us where line

level is

all right so now that we know all of

this

why is it so hard to set an input gain

why is there so much consternation about

it why is there so many approaches about

it

it is simply taking a signal and moving

it from mic level to line level so that

it works properly and transports through

the console properly

right

that's all you need to care about

all right now signal to noise all of

that stuff that comes into play in

analog for sure we can get enough signal

in where we have circuit noise that is

diminished with regard to it etc but i

promise you

that even in analog circuitry

line level is the place where that is

the best

in digital

because we're converting that doesn't

come into play there is no signal noise

at some point we just have bit depth

that is so poor that the signal turns

into noise

okay

so let's get back to our original

discussion here so we have our mic level

signal coming in we need to get it to

line level because the console is built

to work at line level

in our situation that has to do with

zero db

okay not dbfs this is dbvu okay zero db

all right

so let's talk about this for a minute

what do all these different scales mean

all right so

what that means what it means is i take

a mic level signal in and i turn up the

preamp until it is sitting at zero

line level all right i want it operating

somewhere around zero what does that

actually mean in terms of the

electronics part of it what that means

is if i took a direct output from that

channel and went out of the console with

it it would be plus 4 dbu analog

all right in venueland it's called dbr

meaning we have an analog scale

right and 0 db there actually represents

-20 dbfs because it's

digital

right but we've given you it at an

analog scale

but here's the important part to

remember when that cons or that signal

is operating around zero the analog

portion of a console would put out plus

4 dbu

venue would put out plus 4 dbu and pro

tools would put out plus 4 dbu if that

signal is sitting at those levels

okay

all right so zero is you know it's the

same it's just different ways of showing

the damn the the same signal

okay

everybody with me

okay

just different ways to look at the same

thing

all right so let's go back to our

oh no here we go so

uh yeah sorry here's the other piece of

it that we have to pay attention to in

digital right in in analog it's noise

right that's the enemy in noise or in

analog is noise

right as we if we didn't have enough if

that mic mic level signal was too low

noise actual signal noise would compete

with it right that's not the case in

digital what we have in digital is a bit

depth issue

right meaning how many bits are being

used on the signal and here's where

we're gonna we're gonna run into

probably some conflict with recording

engineers etc but i'm gonna try to

explain the difference between these two

things in live and recording

in in our world we work in 24 bit depth

preamps right 24 bit what that

translates to over the scale is 6 db per

bit

okay so if i have the signal operating

at -6 i've used 23 bits of conversion

right minus 12 22 bits

right on down the line right so you just

keep subtracting so what that means is

if i can get a signal rmsy is hanging at

zero line level i'm actually converting

at around 21 bit

that's plenty

that's plenty of bit resolution

especially for live sound all right now

here's the other thing to take into

account here

if my main signal is sitting here and

it's converting at 21 bit

in live sound signal let's say it's a

vocal mic right and we have vocal signal

what's all the signal that's sitting

down here

if this is the vocal what's down here

yeah room background noise amplifiers

drums etc well what do you think those

signals are converting at

yeah very low bit rate right they're not

going to be very pretty that's why it's

very important in digital even though

it's nearly impossible as you're going

to hear on some of the tracks i'm going

to play you today to keep that signal

low and out of the way and the the worst

part about it is if we don't get that

signal coming in properly to line level

if we run it too low

then not only do we get low bit

resolution of the main signal but even

worse resolution of the background noise

right

so it's uber important to get your

levels right on the console yeah

recording so that you're just short of

zero

to maximize resolution yeah

you have to just be careful with it uh

in this and here's the difference

between like the studio mentality and

the live sound mentality

in the studio mentality let's go back to

that situation again where i was just

talking about let's say we're recording

a vocal right

what's all this stuff sitting down here

in the recording

yeah that's your million dollar room

right

so we we don't want that to be recorded

low bit rate at it as well we want to

get all of it recorded hotter

now obviously there's some place where

we can't get more level

you know this this ratio is not going to

change unless we change it

meaning i compress the signal or limit

the signal pre-conversion

pre-conversion

right so if i if i reduce that

pre-conversion and then turn the whole

thing up i now have a much higher bit

rate conversion of my my background

noise my room right so that's the

recording mentality

the problem is

when we do that in live sound we first

of all we don't have the ability unless

we really really put together some

specialized

uh signal paths we don't have the

ability to compress or limit

pre-conversion okay so that's the first

thing if we do it post conversion we're

not gaining anything in bit depth

and we're actually taking all of this

not so well recorded

background noise and moving it closer to

our signal what is this in there this is

echo this is pa system this is symbols

this is you know

that's where all of these heavy heavy

compression techniques for live

microphones

don't serve you very well in live sound

okay you've got to be much more

judicious with it

okay we don't have that luxury of

isolation

that we have in the studio okay you're

with me so far

okay so let's get back to it here so the

idea here again is just to get

maximized operating system here now why

is this more important in live sound or

why is this really important in live

sound because

it plays directly into

fader levels as well

and not only that as you're going to see

here in a second it's also what our

record level

it's our record level as well directly

off the pre and the conversion is also

our recording level so here's the

challenge that we have in live sound

this is it in a nutshell

let's uh let's make this

let's make this the bass drum for a

second okay

if i'm sitting at the console

and i gain up that bass drum and get it

optimized right around line level

and it's not loud enough in the room

what's that telling me

we need a bigger pa system

we need a bigger pa system

right there's nothing i'm going to be

able to do

between here

and there

to magically make that work there are no

plugins to magically make it work and

give me more headroom etc when you turn

it on and there's not enough of it

there's not enough pa

okay

now compare that to the studio do we

ever say there's not enough control room

monitors

no

this is a dynamic that we have to tend

with in live sound right

now here's the other problem that we

have to tend with that is again not in

recording

what do we do let's say let's say it's

well we started out with the bass drum

let's let's stick on the bass drum for a

second

let's say i turn up the bass drum in the

pa i've got my fader set at zero high

resolution and of course i've got my

master setting at zero

but it's now way too loud for the music

i'm going to be presenting this is the

bigger dilemma

now what do i do

where do i turn it down

well so now if i turn it down at the

amps i'm going to penalize the level of

all inputs the potential of all inputs

just because the bass drum was too loud

where do i turn it down

how do i make it right for the music i'm

about to present

what kind of subgroup

yeah you're on you're right on the money

there we have a we have an excellent

student in the audience today thank you

for coming

so

let's play the game though i'll back up

even though you're exactly right let's

play the game because what i see people

do more often than not

is one of two things more often than not

they will turn this down

they say well just turn down the preamp

what's the ramification of that

lower bit rate

lower resolution right

okay

so there was a in analog you can kind of

get away with that

at times but in digital you really can't

get away with it right so we've got to

come up with a way to turn this down the

other part of it that we don't want to

do for live remember we're setting we're

adjusting this to make it right in the

room well we've now also destroyed the

record level

now it's not recording at the right

level either now the guys are going to

get it in post go dude what's up with

your levels well it had to be right for

the room

right

so

the other piece of it like i said is the

digital recorder is tapped right off

that

the other thing is once it's optimized

here it's perfectly set up for effects

processing on the channel meaning gates

compressors etc when this is optimized

for xero you can literally go to the

gate and punch it in without doing

anything on the settings if the

threshold is set right at zero and the

gate will probably start operating

correctly

right if you don't have that if i turn

down that kick drum there to make it

work in the room

let's say i turn it down 20 db maybe

that's what it's got to be for the room

now i've got to find an additional 20 db

of threshold in my noise gate to make it

work

i as all this calculation has got to

take place in my head now to kind of go

well it's down 28

you might not even be able to get enough

threshold to get it to work

right again line level is where the

console is optimized to work

right

so

the other place that comes into play is

if i turn it down i've stolen

gain potential from aux levels if i'm

mixing monitors there now i've taken

away gain from the aux level

just just to get it to sit right in the

room

okay

and here's the bummer about it and this

is probably the thing i see people do

the most they just apply a vca subgroup

to this right

think well i'll just use the vca to do

it and we know what a vca does right as

it moves down

oops i think i got ahead of myself there

as it moves down

it is essentially moving the fader down

right

now that can work to our advantage don't

get me wrong but in this situation to

use it to create an offset or to use it

to set the level in the room

honestly it's the wrong choice

because

you've now stolen any that that same

amount of gain away from that aux bus

you don't really have it optimized in

the aux bus now right so if you had

something sitting outside here maybe

it's not monitor mix in this situation

maybe it's an effects processor or a

compressor maybe it's bus driven

compression now you're in the same

problem right you've stolen a gain away

from there and you're gonna have to make

it up in threshold out there all of a

sudden the the tail starts chasing the

dog a little bit you know

whereas if we make this an audio sub

group and i'm going to give you a piece

of language here to help you kind of

understand this a little better because

subgroup is really not the best term to

use in this situation it really should

be sub master

right it's a sub master

meaning if this is the sub master for my

drums this is going to represent the

overall level of the drums in the room

it's a master fader for the drum kit i

may create a master fader for the

guitars a master fader for the keyboards

etc right it's not a vca it's an audio

subgroup

all right so i can leave this where it's

supposed to be optimized here i still

have a good record level i have

optimized signal for

dynamics processing i still have the

full game potential for any aux buses

pre or post fader

because i've used an audio subgroup

there to set the right level not a vca

which would still gain potential away

post fader

right

and the other thing keep in mind if

you're doing bus style compression if

you've got compression being driven off

of

an aux bus and you have this set up as a

vca every time you move the vca you've

now changed the threshold to the

compressor

you're going to be chasing your tail for

a long time to get that right

okay is this making sense to everybody

right so how do we set gain

rms level to line level

on the console