Setting Limiters

[David Carter]

OK. Let me start by giving myself a few of these...



Having acknowledged that this is an oft-covered subject, let me say in my defense that I did a bunch of searching and found several topics on how to determine the correct voltage to limit to, but nothing on what you do after you connect your meter to the outputs on you amp. I've done this once before when I was setting up my DCX for my previous rig, but now it's time to reset for the new T39's (and again soon for the DR200's). It's been so long that I can't remember what I did to figure out the dB levels I need to set the limiters to in my DCX.

[wallywally]

1. Turn amp attenuators up all the way.
2. Run sine wave (I use 60 hz for subs and 1Khz for mains)
3. Turn the board main up until you exceed your max desired voltage
4. Reduce the threshold in you limiter until you have the desired voltage. Limiter set to 0ms attack and ratio infiniti :1.
5. Test to make sure that no matter how much you turn your board up you do not exceed your desired max voltage.
6. I like to reset my post board gain structure so the limiters are engaged @ 0db on my main slider of my board.

[David Carter]

Thanks. My DCX also has a release setting which is currently set at 407ms. Any thoughts on optimal values for that setting?

[SoundInMotionDJ]

1. Turn amp attenuators up all the way.

When I use that method, I have to take the signal down to the point that it barely registers on any of the meters. So...what I do is this:

1) Turn the amp all the way down.
2) Play a 1kHz signal.
3) Turn the mixer up until it just barely touches the red. (This is about +4dB on my mixer...YMMV).
4) Setup the EQ to pass the signal through unchanged.
5) Setup the limter to just barely limit the signal (about -1dB).
6) Turn up the amp input gain until the output voltage is at the limit you want to set. The limiter may need to be adjusted down to get to a precise final output voltage limit.

If you are an overachiever, you can actually record the output voltage at every 'click' of the amp input gain. Done for every amp channel in use, and you can power match all the boxes even if you need to make a change in the middle of a performance.

From that point, any adjustments I make to the system are 'down' - I will move the EQ down, any of the gains down. What I will not do it turn anything up.

That gives me the maximum range on the channel and master sliders, and provides the largest signal through the entire effects chain. If I were to turn the amp input all the way up...the signal coming off the mixer and passing through the signal chain would be 40-60dB down. That's just not enough signal to noise for my tastes.

--Stan Graves

[RayAbbitt]

1. Turn amp attenuators up all the way.

That is correct (and necessary) for setting limiters. It is NOT correct for setting gain structure for system operation.

When I use that method, I have to take the signal down to the point that it barely registers on any of the meters. So...what I do is this:

1) Turn the amp all the way down.
2) Play a 1kHz signal.
3) Turn the mixer up until it just barely touches the red. (This is about +4dB on my mixer...YMMV).
4) Setup the EQ to pass the signal through unchanged.
5) Setup the limter to just barely limit the signal (about -1dB).
6) Turn up the amp input gain until the output voltage is at the limit you want to set. The limiter may need to be adjusted down to get to a precise final output voltage limit.

The problem with this is that the limiter is no longer providing any kind of protection. The idea is to apply a signal to the amplifier that drives the amplifier to maximum output with the amplifier input attenuators at maximum (they do NOT change the gain of the amplifier by the way) and adjust the limiter to give you the maximum desired output voltage. Done this way NOTHING done earlier in the system will increase the output above max thus protecting your drivers. As far as setting system gain goes, there are a couple of different thoughts there. One says that everything should be set to clip at the same time--including the power amp. Which is all well and fine if you intend to run your entire system all out all the time. The other school of thought (which I subscribe to and you are approaching) is to run everything at close to optimum levels and adjust the attenuator on the power amp for the output you need. As you noted, you will normally get the least system noise this way. The important thing to remember here is that you want to make sure that NOTHING gets driven into clipping or is sounds like crap.

Ideally you should KNOW where each stage of your signal chain clips (and you can't trust the meters to tell you that). If you happen to have an extra piezo laying around you can use it to find the actual level where each stage clips.

If you are an overachiever, you can actually record the output voltage at every 'click' of the amp input gain. Done for every amp channel in use, and you can power match all the boxes even if you need to make a change in the middle of a performance.

And you are nullifying the use of a system limiter. The idea is that NOTHING you can do whether it is adjusting the amplifier INPUT ATTENUATION or applying a stronger signal earlier in the chain can cause the output level to exceed the limited value.

From that point, any adjustments I make to the system are 'down' - I will move the EQ down, any of the gains down. What I will not do it turn anything up.

That gives me the maximum range on the channel and master sliders, and provides the largest signal through the entire effects chain. If I were to turn the amp input all the way up...the signal coming off the mixer and passing through the signal chain would be 40-60dB down. That's just not enough signal to noise for my tastes.

--Stan Graves

This part I agree with. But if you have everything set up right, it doesn't matter if somebody accidentally (or "helpfully") adjusts your amp input attenuators. Your drivers are still protected.

-ray

[Bill Fitzmaurice]

And you are nullifying the use of a system limiter. The idea is that NOTHING you can do whether it is adjusting the amplifier INPUT ATTENUATION or applying a stronger signal earlier in the chain can cause the output level to exceed the limited value.

-ray

+1.

[SoundInMotionDJ]

When I use that method, I have to take the signal down to the point that it barely registers on any of the meters. So...what I do is this:

1) Turn the amp all the way down.
2) Play a 1kHz signal.
3) Turn the mixer up until it just barely touches the red. (This is about +4dB on my mixer...YMMV).
4) Setup the EQ to pass the signal through unchanged.
5) Setup the limter to just barely limit the signal (about -1dB).
6) Turn up the amp input gain until the output voltage is at the limit you want to set. The limiter may need to be adjusted down to get to a precise final output voltage limit.

The problem with this is that the limiter is no longer providing any kind of protection.

The limiter is absolutely still providing protection...but it needs to work in a coordinated way with a second control to protect the speakers. The limiter is still limiting the input to the amp. The amp input gain knobs are just part of the total equation now. As long as no one comes along and moves the amp input gain...and that is something that I can control...since I am the only one who is involved with the setup of my system.

I would never argue that this method is idiot proof. But I would argue that I am not an idiot.

The idea is to apply a signal to the amplifier that drives the amplifier to maximum output with the amplifier input attenuators at maximum (they do NOT change the gain of the amplifier by the way) and adjust the limiter to give you the maximum desired output voltage. Done this way NOTHING done earlier in the system will increase the output above max thus protecting your drivers.

I run into an issue with that method: When my signal chain is setup for unity gain, the limiter in the DCX can not reduce the signal enough to keep the amps output below the desired level with the amp input gains turned all the way up. AND, the limiter will be compressing the signal by about 30dB. That much compression on every signal sounds like crap!

So SOMETHING has to give. What would you suggest?

In this case, I could solve the problem by selling my current amps, and buying some that have a much lower output rating. But, I prefer to have amps that are oversized...more room for future expansion, better heat sinks, the amps will never really get past "coasting", etc, etc.

I could get a mixer that is 0dB based. But, I like this mixer, it's already in the rack...so I think I'm going to stick with the one I have.

Any other suggestions?

As far as setting system gain goes, there are a couple of different thoughts there. One says that everything should be set to clip at the same time--including the power amp. Which is all well and fine if you intend to run your entire system all out all the time.

True. But I don't run my system like that.

The other school of thought (which I subscribe to and you are approaching) is to run everything at close to optimum levels and adjust the attenuator on the power amp for the output you need. As you noted, you will normally get the least system noise this way. The important thing to remember here is that you want to make sure that NOTHING gets driven into clipping or is sounds like crap.

Yup. Since the mixer, EQ, and Crossover will all clip at about the same time...and the limiter will actually catch the signal about 1dB before it clips, I agree. Once you hit the red on the mixer...the sound just starts to suck more.

The only use of the limiter is to protect the speakers from a signal that would cause damage. Given that, I don't really care what it does to the sound...I just want to save my boxes. But, that doesn't mean I want to give up signal to noise ratio if I don't have to.

Ideally you should KNOW where each stage of your signal chain clips (and you can't trust the meters to tell you that). If you happen to have an extra piezo laying around you can use it to find the actual level where each stage clips.

I'm not quite ideal...but in the ballpark for what I'm doing. I have run test signals through the system using a volt meter on the in and out. I have hooked up the piezo (there is no doubt about where the signal clips with those...) I don't have an O-scope. The meters on the DEQ and DCX are "close enough" to showing clipping for what I need. The meter on the mixer is not.

If you are an overachiever, you can actually record the output voltage at every 'click' of the amp input gain. Done for every amp channel in use, and you can power match all the boxes even if you need to make a change in the middle of a performance.

And you are nullifying the use of a system limiter. The idea is that NOTHING you can do whether it is adjusting the amplifier INPUT ATTENUATION or applying a stronger signal earlier in the chain can cause the output level to exceed the limited value.

I am NOT nullifying the use of the limiter. I am making the final limit dependent on TWO controls instead of ONE. The limiter will absolutely still limit the signal that is going to the amp. There will never be a signal that comes into the amp that is larger than the limiter will allow. This signal is always within the amps linear range.

The second control is the amps input gain knob. I have a little table that shows me where to set the input knob on the amp for 50w, 100w, 150w, and 200w of output.

At a typical event, I setup the amp gain to send about 100w to each cabinet. I then pull the master slider DOWN until I am sending 30-50w. It is rare that I need to run the system over that level.

From that point, any adjustments I make to the system are 'down' - I will move the EQ down, any of the gains down. What I will not do it turn anything up.

That gives me the maximum range on the channel and master sliders, and provides the largest signal through the entire effects chain. If I were to turn the amp input all the way up...the signal coming off the mixer and passing through the signal chain would be 40-60dB down. That's just not enough signal to noise for my tastes.

--Stan Graves

This part I agree with. But if you have everything set up right, it doesn't matter if somebody accidentally (or "helpfully") adjusts your amp input attenuators. Your drivers are still protected.

I will agree that in theory, it is possible for someone to come along and adjust the amp input gains. Given how I operate, that is unlikely...but it could happen. I am a one man show, I do all the setup, run the system, and pack it up at the end of the gig.

Someone could think "...he's running those amp inputs at less than max...I'll turn them up for him so that the amps are running full tilt..." (This has never happened to me. I have never had anyone adjust an amp input gain.)

Someone could think "...wow, that joker has a limiter on the output...I will help him to get the most out of his system by turning that limiter off..." (True story. That DJ has been banned for life from ever touching my gear again.)

Someone could think "...this moron plugged his amps into an outlet that I need for the heat lamps at this carving station. I know...I will unplug his amp and move it to another outlet..." (True story...and it's happened more than once over the years. Those banquet guys will unplug anything without even a second thought.)

Given enough time, anyone can find a way to help you all the way to the repair shop.

--Stan Graves

[RayAbbitt]

The idea is to apply a signal to the amplifier that drives the amplifier to maximum output with the amplifier input attenuators at maximum (they do NOT change the gain of the amplifier by the way) and adjust the limiter to give you the maximum desired output voltage. Done this way NOTHING done earlier in the system will increase the output above max thus protecting your drivers.

I run into an issue with that method: When my signal chain is setup for unity gain, the limiter in the DCX can not reduce the signal enough to keep the amps output below the desired level with the amp input gains turned all the way up. AND, the limiter will be compressing the signal by about 30dB. That much compression on every signal sounds like crap!

So SOMETHING has to give. What would you suggest?

As I said, you set the limiters with the amps wide open. This can (and should) be done with no load connected to the amps. But you adjust the amp attenuators for the desired maximum volume AFTER the limiters have been set correctly.

As far as setting system gain goes, there are a couple of different thoughts there. One says that everything should be set to clip at the same time--including the power amp. Which is all well and fine if you intend to run your entire system all out all the time.

True. But I don't run my system like that.

I don't think anybody really does. But you will find that there is a lot of literature around that suggests that.

The other school of thought (which I subscribe to and you are approaching) is to run everything at close to optimum levels and adjust the attenuator on the power amp for the output you need. As you noted, you will normally get the least system noise this way. The important thing to remember here is that you want to make sure that NOTHING gets driven into clipping or is sounds like crap.

Yup. Since the mixer, EQ, and Crossover will all clip at about the same time...and the limiter will actually catch the signal about 1dB before it clips, I agree. Once you hit the red on the mixer...the sound just starts to suck more.

The only use of the limiter is to protect the speakers from a signal that would cause damage. Given that, I don't really care what it does to the sound...I just want to save my boxes. But, that doesn't mean I want to give up signal to noise ratio if I don't have to.

And you don't have to. In no place did I suggest running the amps wide open for normal system operation.

Ideally you should KNOW where each stage of your signal chain clips (and you can't trust the meters to tell you that). If you happen to have an extra piezo laying around you can use it to find the actual level where each stage clips.

I'm not quite ideal...but in the ballpark for what I'm doing. I have run test signals through the system using a volt meter on the in and out. I have hooked up the piezo (there is no doubt about where the signal clips with those...) I don't have an O-scope. The meters on the DEQ and DCX are "close enough" to showing clipping for what I need. The meter on the mixer is not.

You don't need a scope. The piezo will show you the problem before you ever see it on a scope. I've got scopes and distortion analyzers, but I use a piezo for gain testing. (I've got one of these http://www.vizear.com/ClipCop.htm because it is cheap and handy.)

The second control is the amps input gain knob. I have a little table that shows me where to set the input knob on the amp for 50w, 100w, 150w, and 200w of output.

At a typical event, I setup the amp gain to send about 100w to each cabinet. I then pull the master slider DOWN until I am sending 30-50w. It is rare that I need to run the system over that level.

In some respects we are getting into a matter of semantics here. I set my amp attenuators to achieve 6db above my desired spl at the mix position and then bring the masters on the mixer down to achieve the actual desired level. I don't really care what the actual power to the speakers is. If I can't get that level, I didn't bring enough boxes for the job.

From that point, any adjustments I make to the system are 'down' - I will move the EQ down, any of the gains down. What I will not do it turn anything up.

That gives me the maximum range on the channel and master sliders, and provides the largest signal through the entire effects chain. If I were to turn the amp input all the way up...the signal coming off the mixer and passing through the signal chain would be 40-60dB down. That's just not enough signal to noise for my tastes.

Nowhere did I ever say that in normal operation you should run the amp input all the way up. I said to run the amp input all the way up to set the limiters. In actual operation turn the amp input down to achieve the desired spl.

-ray

[Gregory East]

And he's saying he can't do it that way because his amps are too powerful for his limiter to reign in his overdriving mixer, so you'll just have to agree that blowing up speakers is bad.

[bgavin]

Inside voices, please.

[gdougherty]

I have the same issue as SoundinMotion. I bought matching pairs of PLX3602's because I got them cheap and one could easily drive the 4 T48's I built. Reigning back the one for my OT12's seemed practical and even provided enough headroom that I didn't feel bad running 4 OT12 per side if I limited them to about 200W/box for 800W vs the 1700W 2ohm rating. If I turn the amps up, my limiters get set about -24db on my DCX. If I then turn down the attenuators for signal to noise, my limiter kicks in on the signal long before I get to 200W. Granted, my speakers are fully protected, but I now don't have much usable headroom because they're overprotected. Turning down the attenuators keeps them protected by a properly set limiter, gives me the headroom I want, and keeps the inherent system noise low.

If you have a recommendation on how to set things up so I have the headroom I want, with the attenuators down for low noise during normal operation, having set a limiter to protect the speakers with the attenuators all the way up, I'm open to hearing it. I'd love to be able to set things up that way, but I'm not limiting to peak power output, I'm limiting to a bit below RMS so there's no possibility of damage and so I can honestly tell people that's as much as the system will safely do.

[thijs666]

http://billfitzmaurice.net/phpBB3/viewt ... x&start=18

I can start a new topic on this (again, the old one is gone) or you can PM me .

[David Carter]

I have the same issue as SoundinMotion... If I turn the amps up, my limiters get set about -24db on my DCX. If I then turn down the attenuators for signal to noise, my limiter kicks in on the signal long before I get to 200W. Granted, my speakers are fully protected, but I now don't have much usable headroom because they're overprotected.

+1. I tried turning my XTi-4000 all the way up and setting the limiter at 50V for my pair of 3012LF-loaded T39's. It worked out to -20.7db on my DCX. But then when I turn down the amp, I can only get up to 11V before the limiter kicks in.

[Bill Fitzmaurice]

when I turn down the amp, I can only get up to 11V before the limiter kicks in.

As it should be, since what the limiter limits its own output level, and therefore the input level to the amp. Not enough output? Turn up the amp.
BTW, there shouldn't be a S/N problem running with the amp wide open; if there is that indicates a gain structure problem elsewhere. Just because you have a high powered amp doesn't mean you have to run with its volume down low, because all amps run with roughly the same input sensitivity.

[jcmbowman]

From what I've seen it's pretty standard in the industry to run your amplifiers wide open. There shouldn't be any noise or hiss coming from the speakers unless there's a problem elsewhere in your signal chain, as Bill mentioned.

My usual method is to set the limiters with the amps full, then run gigs at 70-80% on the amp until the headliner comes on stage to play. I always prefer to keep a little bit in reserve for when I really need it.