Best Practices in Q-SYS Gain Structure (Part 2)
| Site: | QSC |
| Course: | Q-SYS Quantum Level 1 Training (Online) |
| Book: | Best Practices in Q-SYS Gain Structure (Part 2) |
| Printed by: | Guest user |
| Date: | Saturday, 23 November 2024, 4:00 AM |
Description
Video Transcript
00:07
Welcome back! Let's pick up where we left off.
00:11
Reaching nominal gain in Q-SYS is very simple:
00:14
Plug in your signal and adjust the preamp gain until the input meter level reads about -20.
00:20
That’s it!
00:21
You are going to get a far better result if you calibrate every preamp
00:24
so that you have a uniform -20 dBu nominal,
00:28
rather than having to compensate later in the signal chain in cross points and matrix mixers.
00:33
This is true for every input to the system:
00:36
Microphones, Program material, conferencing feeds….everything.
00:40
There’s one major additional concern when it comes to microphones.
00:44
Microphones will have their own noise floor based on the room they're in,
00:48
the amount of noise in the room, the quality of the microphone etc.
00:51
According to the Avixa standard for mic speech intelligibility, the minimum signal to noise ratio is 15dB.
01:00
If the ambient noise level at the microphone and your nominal level of the talker is less than 15 dB
01:06
then you’re going to find you're in trouble.
01:08
Unfortunately, you can find yourself in that situation all too often,
01:13
particularly when using common ceiling microphones next to air handlers.
01:18
Unfortunately, no matter how great your DSP might be,
01:21
there's no way to fix the signal to noise ratio of a given input.
01:25
AEC algorithms do provide some steady-state noise reduction,
01:29
but when you have poor signal to noise ratio,
01:32
it’s not going to be able to distinguish between signal and noise.
01:35
That’s why the most crucial part of the signal chain is the integrity of that first sample.
01:41
You can gauge that microphone intelligibility in Q-SYS at the meter.
01:46
If nominal level of -20 dBFS has been achieved,
01:50
but the noise floor is above -35 dBFS, we cannot ensure intelligibility.
01:56
Calibrated to -20dBFS nominal, if the noise floor at the input meter is BELOW -35dBFS,
02:04
then it should pass the intelligibility test.
02:07
Once we sample the mic signal,
02:09
most integrators will apply some microphone processing to get the best overall performance.
02:14
The most common mic processing combination seen in the field is high-pass filter,
02:19
parametric EQ and low-pass filter.
02:22
The high pass filter is used to remove low-frequency noise, typically set to 60 or 80 hertz.
02:28
Parametric EQ is meant to remove frequencies that might cause feedback
02:33
and equalize the natural response of the mic in the space.
02:36
The low pass filter is used to remove any unwanted high-frequency noise,
02:41
and each will vary based on application.
02:44
For vocal performance, you’d like to keep as much high frequency as possible,
02:48
while that can be sacrificed in conferencing applications.
02:52
Generally speaking, the goal should be to maintain as much high end frequency as you can,
02:57
however the SIP codecs in a conferencing application compress most of it anyways,
03:02
so you can choose to remove more of the high end energy for the sake of clarity.
03:06
Keep in mind that different components of speech have different frequency ranges.
03:11
Vowels and the fundamental human voice are relatively low frequency.
03:16
Consonant sounds are in the middle range, while sibilance sounds are in the higher ranges.
03:22
If you are looking to get a little more intelligibility,
03:25
look to manipulate the constants and the sibilance.
03:27
If you are encountering feedback, you can address it using an RTA in the space or just by ear,
03:33
but the Notch Feedback Controller component
03:36
is a perfect tool for figuring out exactly what frequencies you're feeding back.
03:40
You can put this into your signal path and follow these instructions to force the system into feedback.
03:46
First, set a fixed filter count to 0 and set a dynamic filter count to 5.
03:53
Then set the “Min Dynamic Frequency” to 80 Hz and the “Max Dynamic Frequency” to 20 kHz.
04:00
Finally, find the threshold of feedback and go slightly over.
04:05
The resulting feedback frequencies will be easy to identify in the NFC block.
04:10
In this example, you see feedback in two specific ranges.
04:15
After you are finished, we do not generally recommend leaving these in the signal path,
04:20
as you’d typically reserve these for use in very difficult environments.
04:24
It’s more effective to use this as an analysis tool and then create a parametric EQ that is a bit more gentle
04:30
to help mitigate those frequencies without affecting too much of the overall tone.
04:35
Keep in mind that this will be an iterative process.
04:38
For example, you should always start with the lower frequencies
04:41
because those are typically going to be fundamental of the problem frequencies.
04:44
If you fix those, you're less likely to have feedback in the higher frequencies as a result.
04:49
When you have transferred the information that you've learned from the Notch Feedback Controller
04:54
over to your parametric EQ you should have mitigated most of the risk of feedback.
04:59
Alright, that's a good place to pause. Move on to the next video whenever you're ready.
Lesson Description
(Part 2 of 4) Learn to do's and don't for setting good gain structure within Q-SYS, particularly within a meeting room scenario.