Gain Structure | FOH Masterclass ft Robert Scovill | Hillsong Creative Audio Training
Summary
TLDRThe 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
🎛️ 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.
📊 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.
🎚️ 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.
🔊 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.
Mindmap
Keywords
💡Gain Structure
💡Input Gain
💡Faders
💡Line Level
💡Bit Depth
💡Signal-to-Noise Ratio
💡Audio Subgroup
💡VCA
💡Dynamics Processing
💡Headroom
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
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