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Best Gain Staging Practices for Wireless Mics

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Best Gain Staging Practices for Wireless Mics

PostPosted: Sat Dec 15, 2018 10:26 pm
by ijosephwalsh
We recently purchased a new wireless microphone system for our school gymnasium. I have been playing around with gain staging for the last week and I think I've finally hit the nail on the head but wanted to get everyone's opinion.

We purchased the Audio-Technica System 10 PRO with two handheld transmitters. Those mics are connected to a rack-mount Allen & Heath mixer which goes out to an amp for the speakers in the gym.

When first getting started with setting the gain staging, I was a little overwhelmed with all of the possibilities for setting it up. The handhelds had built in trim control, the receiver had an output knob, and the mixer, of course, has a gain control on each channel. After a little research, I think I have come up with the best setup for our situation.

To obtain the best signal-to-noise ratio, I opted to keep the handheld trim control at its highest setting. For this model, Audio-Technica recommended leaving the receiver at max output for most situations. Our amp's gain was also already set properly, so that pretty much left the mixer as the only area of uncertainty as for how I was going to set it up.

I struggled to get good, decent sound without getting some sort of noise or feedback. Then I discovered that the Audio-Technica System 10 PRO has a receiver output of 0 dBV, which we know as line level. I was incorrectly treating this system, thinking that it would need considerable gain at the mixer to sound good. While PFL levels did look good, I was still on the verge of getting feedback (a very reflective gymnasium) and had quite a bit of noise. I opted to engage the pad key and bring the gain knob up to unity gain on the mic channel. I was blown away at how much better this sounded. The noise was considerably lower, and I was able to yell into the mic with no feedback.

Lesson learned: wireless mic systems are a whole different ball game than regular mics and have much more wiggle room for what sound you are getting. I hope that the way I set it up properly represents good gain staging and setting up a good signal chain. I'm interested to hear what you all think! What do you guys do in live sound environments for gain staging wireless microphones?

Re: Best Gain Staging Practices for Wireless Mics

PostPosted: Sun Dec 16, 2018 12:21 am
by Sam Spoons
I think you may have been assuming a microphone would send a typical mic level signal to the desk but in this case the signal was much higher and close to line level. According to Wiki. 0dBV is a consumer 'reference level' but most consumer devices actually use -10dBV as 'line level. Pro gear uses +4dBU (which, I believe equates to about 13dB higher than -10dBV due to the different units). A microphone signal would usually be 30 or more dB lower so that's why engaging the pad on the desk and setting the gain as you did resulted in a huge improvement win sound.

It seems to me that you did everything else pretty much right but setting each adjustable gain/trim for the strongest signal without clipping (but leave some headroom for shouters) working from the transmitter and on through the signal path.

Re: Best Gain Staging Practices for Wireless Mics

PostPosted: Sun Dec 16, 2018 12:25 am
by Wonks
You may be better running the receiver into a line input on the mixer (though there may not be one so that's what the pad's for). Which A&H mixer do you have?

Re: Best Gain Staging Practices for Wireless Mics

PostPosted: Sun Dec 16, 2018 12:32 am
by Sam Spoons
ijosephwalsh wrote:While PFL levels did look good, I was still on the verge of getting feedback (a very reflective gymnasium) and had quite a bit of noise. I opted to engage the pad key and bring the gain knob up to unity gain on the mic channel. I was blown away at how much better this sounded. The noise was considerably lower, and I was able to yell into the mic with no feedback.

Just re-reading your post and this paragraph concerns me slightly, yelling into a mic may trigger feedback if the system s already on the verge but a small reduction in system volume should bring it back from the brink. This doesn't necessarily mean the system gain structure is right though as even with it wildly wrong turning the volume down will at some point remove the risk of feedback.

Re: Best Gain Staging Practices for Wireless Mics

PostPosted: Sun Dec 16, 2018 12:54 am
by ijosephwalsh
Sam Spoons wrote:
ijosephwalsh wrote:While PFL levels did look good, I was still on the verge of getting feedback (a very reflective gymnasium) and had quite a bit of noise. I opted to engage the pad key and bring the gain knob up to unity gain on the mic channel. I was blown away at how much better this sounded. The noise was considerably lower, and I was able to yell into the mic with no feedback.

Just re-reading your post and this paragraph concerns me slightly, yelling into a mic may trigger feedback if the system s already on the verge but a small reduction in system volume should bring it back from the brink. This doesn't necessarily mean the system gain structure is right though as even with it wildly wrong turning the volume down will at some point remove the risk of feedback.

Very good point. I should have made myself clearer on this; I was more or less talking louder than normal to imitate someone who may talk into the mic louder than I do. We use the rack-mount Allen & Heath MixWizard WZ3 16:2, so as I was yelling (more or less shouting), I wanted to make sure that I was just hitting around 0 on the mixer and not going into the yellow and certainly not the red. As I talked like I normally would I was bouncing at a comfortable level, which is more than likely what most people will do anyway. To respond specifically to your concern—I was only on the verge of getting feedback from yelling while the gain on the mixer was being used as a mic preamp. After I engaged the pad and set the gain to unity on both the pot and faders, I had no indications of feedback whatsoever!

Re: Best Gain Staging Practices for Wireless Mics

PostPosted: Sun Dec 16, 2018 12:57 am
by ijosephwalsh
Wonks wrote:You may be better running the receiver into a line input on the mixer (though there may not be one so that's what the pad's for). Which A&H mixer do you have?

Very good idea. It is the A&H MixWizard WZ3 16:2 rack mount. I was actually just hired for this position at our school district, so I haven't really explored with some of the inputs on the mixer yet. I did have to open the back of the rack to replace the mic system, but just reused the existing XLR cables with the new system.

Re: Best Gain Staging Practices for Wireless Mics

PostPosted: Sun Dec 16, 2018 1:10 am
by Sam Spoons
Sounds like you have some experience then so ignore may second post and refer to my first and Wonks' replies. :thumbup:

Re: Best Gain Staging Practices for Wireless Mics

PostPosted: Sun Dec 16, 2018 2:44 am
by MOF
Putting the handheld mic’ gain to maximum might cause distortion and/or heavy limiting. If there’s a meter (tricolour led most likely) you should use that first to set a good average level before worrying about the receiver and mixer levels.

Re: Best Gain Staging Practices for Wireless Mics

PostPosted: Sun Dec 16, 2018 3:17 am
by ijosephwalsh
MOF wrote:Putting the handheld mic’ gain to maximum might cause distortion and/or heavy limiting. If there’s a meter (tricolour led most likely) you should use that first to set a good average level before worrying about the receiver and mixer levels.

Very good thing to be aware of. Getting it right at the source is crucial, and in my case specifically, the receiver does have a meter for monitoring the level before the signal is passed to the desk. Audio-Technica recommends that the loudest sounds into the mic just barely turn the "Audio" light on the receiver yellow. Any red and the transmitter gain should be lowered. Fortunately, in my case, I was able to keep the gain up all the way on the transmitter where even the loudest finger tap or shout didn't turn the light red. Great point!

Re: Best Gain Staging Practices for Wireless Mics

PostPosted: Sun Dec 16, 2018 9:27 am
by Sam Spoons
Generally, for speech, the highest gain setting is required, a singer will probably need it turning down, My ancient Sennheiser EW series transmitter, IIRC, has four settings, 0dB, -10dB -20dB and -30dB, the loudest singers sometimes need the -30dB setting to avoid clipping the handset.

Re: Best Gain Staging Practices for Wireless Mics

PostPosted: Sun Dec 16, 2018 11:51 am
by Wonks
If it's not used just for speech but for a singer in a band context with on-stage amplification and drums, then don't forget that the mic will be picking up a fair bit of that too, so the mic signal will be stronger than if it was just the singer themselves.

Re: Best Gain Staging Practices for Wireless Mics

PostPosted: Sun Dec 16, 2018 3:01 pm
by Exalted Wombat
The only special issue with a wireless mic system is the on-mic trim control. There's a compressor/limiter in front of the transmitter stage. You don't want to be hitting it too hard, if at all. It sounds bad, and increases the possibility of feedback. The highest setting is probably suitable for speech or a weak singer. A more confident singer will need it turned down a bit.

Apart from that, just follow normal gain-staging practice, keeping in mind that the performance WILL be louder than the sound check! And that your primary job is to enable a good performance through good monitoring, both of the music and the vocalist. You can point a speaker or two at the audience as well if you like. (That was not a joke.)

Re: Best Gain Staging Practices for Wireless Mics

PostPosted: Sun Dec 16, 2018 3:04 pm
by Exalted Wombat
Wonks wrote:If it's not used just for speech but for a singer in a band context with on-stage amplification and drums, then don't forget that the mic will be picking up a fair bit of that too, so the mic signal will be stronger than if it was just the singer themselves.

You feel that a high noise floor is ADDED to the peak signal?

Re: Best Gain Staging Practices for Wireless Mics

PostPosted: Sun Dec 16, 2018 3:06 pm
by Wonks
It's certainly added to the vocalists input which will raise the peak output a bit.

Re: Best Gain Staging Practices for Wireless Mics

PostPosted: Sun Dec 16, 2018 3:41 pm
by Mike Stranks
Exalted Wombat wrote:The only special issue with a wireless mic system is the on-mic trim control. There's a compressor/limiter in front of the transmitter stage.

Not if it's a digital system. They don't use companders.

Re: Best Gain Staging Practices for Wireless Mics

PostPosted: Mon Dec 17, 2018 1:26 pm
by Tim Gillett
Mike Stranks wrote:
Exalted Wombat wrote:The only special issue with a wireless mic system is the on-mic trim control. There's a compressor/limiter in front of the transmitter stage.

Not if it's a digital system. They don't use companders.

No they dont need them thankfully. But there may be some sort of limiter in there. The fact that there's a gain trim suggests the front end has more dynamic range than downstream of it, hence the need for a gain trim.

Re the trimmer, the OP believed that setting it to maximum gain would give best S/N. Without special knowledge of the particular wireless mic, I'd start by setting it to a mid position.

Re: Best Gain Staging Practices for Wireless Mics

PostPosted: Mon Dec 17, 2018 1:52 pm
by Wonks
Here's the system manual. https://www.audio-technica.com/cms/resource_library/literature/c6bd470b3c10f634/atw_1301_english_web.pdf

There's certainly some contradiction on the receiver output level within the manual as Fig B on page 4 states the XLR is for connection to a mic level input, whilst the specification table on page 10 states the XLR output is 0dBV (and the unbalanced output is at +6dBV). The OP's experience tends to indicate the latter information is correct.

The instructions for the mic gain adjustment basically tell you to turn it all the way up, then only to bring it down if the signal appears to overload. AT are happy with a green or peaking yellow indicator; just not red. So it appears to be more of an attenuator than anything else, just in case it does get used for miking a really loud source, such as a drum or a guitar amp etc.

Re: Best Gain Staging Practices for Wireless Mics

PostPosted: Mon Dec 17, 2018 11:34 pm
by Tim Gillett
Thanks for that info from the manual Wonks.