Gain staging: Part 2
| Site: | QSC |
| Course: | House of Worship Audio Training |
| Book: | Gain staging: Part 2 |
| Printed by: | Guest user |
| Date: | Thursday, 21 November 2024, 7:24 AM |
Description
Lesson Description
In this video we continue our explanations on gain staging workflow and focus on setting up mixer preamps for optimum performance as well as dialing in the channel settings and processing.
Video Transcript
00:13
Hello and welcome to ‘How to gain stage your entire system’ part 2.
00:17
In part 1 we went over the first part of this workflow
00:19
and showed you how to set the gain levels for your amplifiers and loudspeakers.
00:23
In this video, we are going to look at how to properly set up the gain structure in your mixer,
00:27
and how to maintain that gain structure for the entire show.
00:30
Let’s dive right in and start setting the gain levels for our mixer.
00:34
The first thing we’re going to look at are the channel meters.
00:37
We’ve all seen meters on mixers.
00:39
But what are they telling us?
00:41
One important point is the 0 point.
00:43
This is where meters turn from green to yellow.
00:46
0 represents the nominal operating level of the mixer.
00:50
Think of nominal as meaning average.
00:52
When your signal is at its average level, it should be sitting right around 0 on the meter.
00:56
At the top of the meter, we hit peak – going into the red.
01:00
That is the point at which the signal level is trying to exceed the capabilities of the mixer’s circuitry
01:04
and – well – clip happens.
01:08
Between 0 and Peak is headroom and that’s where the dynamic peaks in your signal should sit.
01:14
Think of dynamic range like a highway.
01:16
On one side of the highway, we have a wall.
01:19
That represents clipping.
01:20
On the other side, we have a steep slope into a ditch.
01:23
This will be the noise floor.
01:26
Now imagine a big truck on the highway.
01:28
This represents the signal.
01:30
We want to keep the truck steady on the highway in between the wall and the ditch.
01:35
If we get too close to the ditch, we’re going to get stuck in the weeds.
01:38
If we get too close to the wall, we might break a mirror – or worse.
01:43
Now we also have a lane on the side of the ditch for traffic going the opposite direction.
01:47
We don’t want to be in that lane.
01:49
We want to keep the truck closer to the wall, but with just enough space to so that we don’t make contact.
01:54
We will call this the “Target operating range”.
01:57
Let’s start up our truck and get on the road.
02:00
We’ll use the channel meters to monitor and set the preamp gain level
02:03
so let’s leave our faders all the way down for now.
02:07
We also want to make sure our EQ filters are all set to 0, representing Unity gain at this gain stage.
02:13
Our compressors, gates and effects should all be bypassed.
02:16
An easy way to ensure this starting point is by simply recalling the Default factory scene.
02:22
Alright, let's start connecting components and staging our gain.
02:26
Let’s start with a microphone.
02:28
We connect the microphone to the mixer and ask the performer to sing or play, as they will during the show.
02:34
As we increase the trim setting,
02:35
we will begin to see the signal from the microphone increase on the channel’s level meter.
02:40
We’re not going to hear anything yet, because the faders are down.
02:43
Let’s keep increasing that gain level
02:44
until we see the peak levels in the signal begin to clip the channel.
02:48
You will know when you start to clip because the meter will light up red.
02:51
This means the channel has been overdriven to the point of distortion –
02:54
our truck is scraping the wall.
02:56
As soon as we see this, we’re going to bring the gain back down until clipping stops.
03:01
Theoretically, the gain for this input should now be properly set.
03:05
However, in the excitement of the performance,
03:08
it is likely that the performer will be singing or playing louder than they did during sound check.
03:12
In addition, there will probably be more stage noise.
03:15
Therefore, we’re actually going to take the input trim down a bit more.
03:20
Say somewhere between 3 dB and 12 dB
03:23
Think of this as an extra cushion to protect the system from unexpected spikes in the signal level.
03:28
For instance, a drummer laying down a rim shot
03:31
way louder than anything he delivered during sound check.
03:33
OR the drummer accidentally smacks one of the drum mics itself during a fill.
03:38
Things like this happen.
03:39
mostly from the drummer.
03:41
Ideally, what we want is for the channel peaks to be hitting into the yellow.
03:45
Occasional, brief clipping incidents
03:47
when a performer becomes overly enthusiastic won’t ruin the show.
03:50
But overall, you should avoid clipping,
03:52
while still allowing the signal peaks to get into that yellow area
03:55
For now, our first channel should be set.
03:57
Let’s move on the next channel
03:59
and repeat the process for all of the preamps on the channels we’ll be using.
04:03
Now that we have set our preamp levels set, I want to talk to you about Unity gain.
04:07
Unity gain is the point at which a gain stage is neither boosting
04:10
nor attenuating – or cutting – the signal.
04:12
In other words, when we set a gain stage to unity gain,
04:14
the level of the signal passing through the stage is unaffected.
04:18
This is an important reference point that can be used to calibrate each stage in the system.
04:22
There may be instances where an instrument can have extreme dynamic peaks.
04:26
If you set the input gain trim to avoid clipping, the average signal level may be lower than you want it to be.
04:32
In these cases, TouchMix has an additional digital gain stage
04:35
which allows for + or – 15dB to be applied to the signal
04:39
To access the digital gain, open the channel by pressing the name above the fader.
04:44
Now navigate to either the overview screen or the setup screen.
04:48
The digital gain control can be found on either page.
04:51
The digital gain is also useful if you need to save your gain settings in a scene.
04:55
The analog trim knobs are not recallable,
04:57
so utilizing the digital gain is a great way to record your gain settings.
05:01
To do this, we will want to set all of our analog trim knobs to a uniform level.
05:05
Say noon or 1 o’clock.
05:08
Now depending on what the signal level is for each input,
05:10
we can adjust the digital gain to make up or attenuate what may still be needed.
05:15
Once the preamp is dialed in, you can increase your channel level and send signal to the loudspeakers.
05:20
We’ll use unity on the output fader as a base to start from.
05:23
Remember, Unity is the point in any gain stage where the signal is neither boosted nor attenuated.
05:29
Generally, you should be setting most of your channel faders somewhere between Unity and -10 dB
05:34
as you get your mix dialed in.
05:36
Of course, there are exceptions.
05:38
Vocals and solo instruments may need to be pulled up slightly above Unity.
05:42
In addition, there may be other things that should be less prominent in the mix – like
05:46
that one person whose vocal harmony is a bit pitchy.
05:48
You know who you are...
05:50
If you are mixing for monitor wedges, there are some inputs – like drum overhead mics
05:54
that don’t need to be in the monitor mix at all.
05:57
You should rarely, if ever need to push a channel fader all the way to the top.
06:01
As you add channels, the output level will increase with each new signal that is introduced,
06:05
but it is not a linear increase.
06:07
In fact, you might not notice much of a change at all in the output meter.
06:11
While you’re bringing up the input channel faders,
06:13
feel free to adjust the output fader to achieve the overall system volume you need.
06:17
What if the mixer output meter goes into the red?
06:19
Well, if you’ve set up your amplifiers and active loudspeakers
06:22
according to the first video in this series, it means that you are out of PA
06:26
and you need to back the output fader down until the red goes away.
06:31
Channel EQ, dynamics and effects will affect your mix
06:33
but on most modern digital mixers- even extreme settings will not cause clipping distortion
06:37
as long as you’re not overdriving the mixer’s output.
06:40
Changes made to these stages won’t affect the channel meter
06:43
as that meter is showing the preamp level alone.
06:45
When adjusting channel processing we are going to use our channel fader
06:48
to balance out the signal level going to the main output.
06:52
Now of course, there may be situations where the gain needs adjusting further
06:55
once the performance or event begins.
06:58
Similar to what we mentioned earlier- maybe during sound check,
07:00
the guitar player sets his amp volume to a reasonable level.
07:03
Then, the show starts and he cranks it up to 11, because the crowd is much louder
07:08
Just an example of course.
07:10
I’m sure that’s never actually happened.
07:12
On the other hand, maybe a vocal mic is passed to a different person at some point during the event.
07:17
If that new person is much softer spoken than the last then the signal entering the preamp
07:22
is no longer within the target operating range.
07:25
When these things happen, go ahead and adjust the input gain trim.
07:29
Just remember that changing input sensitivity by changing the input trim will also affect
07:34
the level of that channel everywhere it’s going – monitors, FX and main output.
07:39
So, you may need to make adjustments elsewhere in the channel as well.
07:43
At this point, we have our mixer gain structure all set.
07:46
From here, the signal passes from the outputs to the amplifiers or active loudspeakers,
07:50
which would be the final stage in the gain structure.
07:52
And because we’ve already set this up in our first video,
07:55
our workflow is complete!
07:56
Now that we’ve seen this whole process, and understand the practice behind it-
08:00
TouchMix actually has two tools that will help you dial in your gain settings during the show.
08:05
The first tool is the mini-faders display at the top of the screen.
08:08
The mixer monitors all the inputs for clipping and will turn a mini-fader red
08:13
if the channel it represents has been overdriven.
08:15
Just go to the corresponding gain trim and nudge it back a little bit.
08:19
The mini-fader will stay red until you push the Clear Clip button.
08:22
There is another great tool called the Gain Wizard
08:25
that will monitor all your inputs for clipping during the entire show.
08:29
The Gain Wizard doesn’t just tell you that clipping took place.
08:31
It tells you how severe the clipping was and how much to adjust your Input Trim.
08:36
To access the Gain Wizard- press the ‘Wizards” button and select “Gain Wizard” on the screen.
08:42
The Gain Wizard will show you which channels have been clipping and at what intensity.
08:47
Each clip indicator has four LEDs.
08:50
When the channel clips, all you have to do
08:52
is dial back the input trim the same number of ticks as indicated by the LEDs.
08:57
Then reset the Gain Wizard and see if the clipping stops.
09:00
Continue this process until the channel is no longer activating any of the clip LEDs.
09:05
Because the Gain Wizard is looking for clipping incidents over time,
09:08
it gives less weight to the drummer sticking the mic one time
09:11
than it does to a guitar amp that’s been cranked to 11.
09:14
The Gain Wizard is an excellent tool for maintaining the nominal level throughout the entire performance
09:19
as these things have a tendency to fluctuate.
09:22
If you would like more info on the Gain Wizard itself, you can check out our dedicated training video on this topic.
09:27
You will be able to find the link in the description to this video.
09:30
One handy little tip I will leave you with- in an ideal gain structure,
09:34
if clipping does occur, every stage in the system will clip simultaneously.
09:39
And with that, we have successfully set up the gain structure for our entire system.
09:43
That’s all for this video.
09:44
Thanks for watching and we’ll see you next time.