Video Transcript
Best Practices in Q-SYS Gain Structure (Part 3)
5m 10s
00:07
Alright, on to the next section.
00:10
Once our signals are processed, they will typically be routed to some type of mixer.
00:15
At its base, the Matrix mixer is relatively simple.
00:19
It’s user assigned and the output level is simply a sum of what is mixed in that output.
00:24
The automixer, on the other hand, requires no user operator,
00:28
and the output level is constant regardless of the number of open mics.
00:33
The matrix mixer allows you to adjust crosspoint controls
00:36
by adjusting the relative level of each input to each output.
00:41
Theoretically, if your inputs enter the matrix mixer at a nominal level,
00:45
changing the relative input and output levels should be simple.
00:49
Crosspoint mutes can be enabled to turn routing on and off without changing the gains.
00:54
Automixers are used mostly for conferencing and speech reinforcement
00:58
and use an adaptive threshold for gating.
01:01
The most important feature of the Automixer
01:04
is that it keeps the overall output level constant regardless of the number of mics open.
01:09
We suggest that the maximum number of microphones, or max NOM,
01:14
be between one and three, which makes sense if you think about it.
01:18
You need one mic for the guy that’s talking, another mic to argue with the first guy,
01:22
and a third mic to tell the other two guys that their both loud-mouth jerks, right?
01:26
Now, there are several controls in this component that you can use to fine tune, but realistically,
01:31
what you should focus on is the “level above noise” which controls WHERE you gate on.
01:38
In this example with eight inputs, the adaptive algorithm will calculate an average noise floor.
01:44
Then, when a microphone signal exceeds a certain signal,
01:47
in this case 10 dB above the overall nose floor, the microphone will gate open.
01:53
In this scenario, the NOM is set to one and as you can see, there is no attenuation.
01:59
Then when I open two mics, there is 3 dB of attenuation…
02:04
… then when you have four NOMs, you get 6 dB of attenuation.
02:08
You get the idea.
02:09
Each doubling in the number of open mics will add three dB more in the total signal
02:15
so the component pulls -3 dB out by attenuating the overall output.
02:20
Ideally, no matter how many mics I open
02:23
I'm never going to go over that initial level you started with at one open mic,
02:28
ultimately keeping you out of the possibility for feedback.
02:31
Next let’s talk about the Q-SYS gain sharing automixer,
02:35
which is based on the Dan Dugan gain sharing algorithm.
02:38
Its goal is to allow a maximum gain of zero by allowing each mic to share the total available gain.
02:45
In the case of one talker, that one mic is granted all the mixer gain.
02:51
However as the number of talkers increases, each mic is granted less of the total mixer gain.
02:57
In reality, gain-sharing automixers work well in systems with fewer microphones.
03:02
When your system needs over 8 microphones or in installations with acoustical challenges,
03:08
we strongly recommend using the gating automixer OVER the gain sharing automixer.
03:13
Putting those things into an overall signal flow from left to right, you have inputs,
03:18
calibrated to -20 dBFS nominal, with some standard EQ, your choice of automixer,
03:25
and output signal conditioning to tune the room, and then the output blocks.
03:30
One thing to note is that there are no user level controls for microphones ahead of the automixer.
03:36
The automixers take the noise level in the room and the level at each mic into account when deciding who gates,
03:42
so allowing user level control could be a problem here.
03:46
When it comes to dynamic processing options for microphones,
03:49
you could employ a compressor which primarily is going to level off loud talkers.
03:54
For spoken word,
03:55
feel free to be fairly aggressive on these but applying these to vocal performance,
04:00
make sure to use that much more carefully.
04:02
The drawback of the compressor is that it doesn't increase the level of quiet talkers.
04:08
Your other option is to use an automatic gain control.
04:12
You get help for quiet talkers and loud talkers.
04:16
However, it reacts slower than a compressor does.
04:19
Furthermore, if the signal to noise ratio of that microphone is not tuned properly,
04:24
then the automatic gain control will exacerbate the issue.
04:28
For example, in most cases, a user can tune out constant static noise.
04:34
But if the AGC is bringing noise up and down in volume,
04:37
it gets harder for the user to ignore the issue.
04:40
Sometimes in noisier installations, you might be tempted to put a noise gate before the automixer.
04:46
DO NOT EVER DO THIS.
04:49
This is a common attempt to solve a problem that should really be solved elsewhere.
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Remember the automixer needs to know the noise level to decide who gates.
04:59
A gate ahead of that will just confuse the algorithm.
05:03
Alright, let's wrap up that subject here and then we'll move on to the next part in the next video.
Lesson Description
Best Practices in Q-SYS Gain Structure (Part 3)
5m 10s
(Part 3 of 4) Learn to do's and don't for setting good gain structure within Q-SYS, particularly within a meeting room scenario.
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Best Practices in Q-SYS Gain Structure (Part 3)
5m 10s