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Ultradrive DCX2496 Gain, Clip & Limiter Setup

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Biggus View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Biggus Quote  Post ReplyReply Direct Link To This Post Topic: Ultradrive DCX2496 Gain, Clip & Limiter Setup
    Posted: 29 September 2010 at 10:10am

I’m still quite new to professional PA setup so please forgive me if some of the things I ask are obtuse, but I’m still learning. I’ve done a search on the forum but can’t find direct answers to what I want to know.

At present I’m setting up my berry DCX2496, I have the X-over and outputs configured to tri-amp as my system runs three ways, tops, mids and subs. The system is wired up Mixer – EQ – DCX – Amps. I’ve read that a good method to setup a sound system is to calibrate the VU meter  levels of each device in the chain, for example if my mixer was reporting the output program is bouncing at about 0db than I’d adjust the input gain on my EQ & DCX to match this so everything is bouncing the same, I can understand the logic in doing this as if the mixer reports its not clipping then you know nothing else in the chain is either, but according the vu meters on the DCX it reports it goes to 0db then starts clipping at anything louder and the mixer/EQ has a +10db before they do, trying to put this in to logic terms does this mean I will have to always play my program material at 0db and no louder to prevent clipping or am I missing something here?  
 
Another thing I can’t get my head around is what to set the outputs levels of my DCX before going to the amps, they seem a lot lower than the input levels I presume this is because the signal is broken up into it separate frequency bands i.e tops, mids and bass, should I set the gain of the outputs db to match the input db so each of the amps is getting its maximum input level?
 
I would also like to set my system up so nobody can turn the increase the volume of the amps. I’ve read the best way to do this is to turn the volume on the amps to maximum and then set the output limiter up on the dcx, I’m aware on how to set the limiter up on the DCX but taking in the above to consideration would I set my limiter at the clip level or  much lower?  or would  I be better setting up some kind of dynamic eq to turn the volume down when the DJ goes into clipping? 
 
I would be very grateful of any answers or advise.
 
Kind Regards
Mark Biggus
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JaKe View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JaKe Quote  Post ReplyReply Direct Link To This Post Posted: 29 September 2010 at 10:44am
The levels on the DCX are a little confusing 0dB on the DCX is actually +22dBu.
For overall protection look at a Drawmer SP2120 or an AVC2 as the DCX limiters will not protect against over enthusiastic DJ's etc.
Dynamic eq's may help but that isn't really what they were intended for  and use a lot of cpu. - why the &*@! they didn't build in a gain reduction option into the unit is beyond me.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote djyves Quote  Post ReplyReply Direct Link To This Post Posted: 29 September 2010 at 10:45am

The 0db on the vu meters of the dcx, are the limits of the dcx itself.

The input and output levels on your dcx:
Start with just 0db, then if there's anything missing, turn your subs, mids, highs up.
 
So you will need to set your limiters much lower than 0db (according to the vu on the dcx), connect your amps without speakers to your dcx. then turn the thereshold back until the clip lights of your amps go out, and then set it 0.5db or so lower, just for safety.
(Then connect your speakers and) drive your dcx in the limit and check if the limiters work.
"If brute force doesn't work, you're just not using enough!"
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Post Options Post Options   Thanks (0) Thanks(0)   Quote djyves Quote  Post ReplyReply Direct Link To This Post Posted: 29 September 2010 at 10:47am
mmm... same time.
 
Like Jake said, the limiters on the dcx are not an good protection against some (enthousiast) dj's


Edited by djyves - 29 September 2010 at 10:48am
"If brute force doesn't work, you're just not using enough!"
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Biggus View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Biggus Quote  Post ReplyReply Direct Link To This Post Posted: 29 September 2010 at 11:30am
Thanks for your replys its starting to make sense now.
 
Originally posted by JaKe JaKe wrote:

The levels on the DCX are a little confusing 0dB on the DCX is actually +22dBu.
As if I'm not confused enough already! This unit must clip high then as all my other equipment clips at +12db. Where would +10db be on the be on the dcx input vu so I have a idea if my inputs are bouncing OK.
Originally posted by djyves djyves wrote:

Start with just 0db, then if there's anything missing, turn your subs, mids, highs up.
Lol where is 0db on this DCX VU meter?
 
For the situation where I don't want people turning my amps up would I be right in saying that if I turn my amps to full and then reduce the gain on the dcx output channels on until the clip light just goes out or my prefared sound levels,  I just think this way nobody will be able to turn the amps up any louder and then just set limiter just above this volume so no idiot can try turning it up on the eq volume etc? would this be a sensible idea?
 
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Tony Wilkes View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony Wilkes Quote  Post ReplyReply Direct Link To This Post Posted: 29 September 2010 at 12:11pm
I don't understand why you reckon the limiters are no good for stopping Idiot DJ's. They work perfectly if set right. The sound does degenerate badly if they are ragged senseless but the gear is protected and the DJ is shown for the Knob that he is.

Tony

www.forteaudio.eu - BMS - db-Mark Processors - Lexon (SAE)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote colinmono Quote  Post ReplyReply Direct Link To This Post Posted: 29 September 2010 at 5:01pm
Originally posted by Biggus Biggus wrote:

As if I'm not confused enough already! This unit must clip high then as all my other equipment clips at +12db. Where would +10db be on the be on the dcx input vu so I have a idea if my inputs are bouncing


As Jake said, full scale i.e. 0dB on the markings (0dBFS for short) on the Ultradrive = 22dBu. This is because it is a digital unit, meters on digital kit are often marked up like this, showing the dB relative to the "full scale" i.e. the maximum voltage the input can handle. It is very confusing when you've only used analogue kit before.

+10dBu = -12dBFS on the Ultradrive
0dBu = -22dBFS on the Ultradrive

For most analogue pro audio gear, 0dB on the VU meter equates to +4 dBu at the master output. This is not a hard and fast standard, but its a reasonable rule of thumb. The Vestax mixer I use measures about 4.5dBu when the 0dB VU LED's are lit. Another example - from the Allen & Heath Xone 62 Manual: "Meter ‘0’ represents +4dBu at the XLR outputs".

So...

0dB on Mixer = -18 dBFS on the Ultradrive
+10dB on Mixer = -8 dBFS on the Ultradrive

This calculator is useful in getting your head round dBV, dBu and VRMS:

http://www.sengpielaudio.com/calculator-db-volt.htm


Edited by colinmono - 30 September 2010 at 5:13pm
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Biggus View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Biggus Quote  Post ReplyReply Direct Link To This Post Posted: 29 September 2010 at 5:17pm

@Colinmonro> Thanks for the info.

Just to make it clear if I was plugging in my analog mixer in to the ultradrive should I be bouncing about -12dBfs on on the VU meter before the analog signal goes into clip?
 
--- Don't want to make this even more confusing but if I was using a digital input would I bouncing right up to 0dbfs
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Post Options Post Options   Thanks (0) Thanks(0)   Quote colinmono Quote  Post ReplyReply Direct Link To This Post Posted: 29 September 2010 at 5:33pm
Personally, I tend to come at it from the other end - look at what signal your amplifier needs to drive it to full output, and then set the limiter on the ultradrive so you don't go over that.

E.g.

If your amplifier input sensitivity = 1 VRMS = 0dBV = 2.2dBu
Set output limiter on Ultradrive to -19.8dBFS = 2.2dBu

Now, if you play your music so you are hitting -2dB on your mixer (0dB on analogue meters is usually +4dBu, so -2dB on the meter should correspond to +2dBu output), you should be just bouncing off the limiter (assuming the Ultradrive and EQ gain settings are at unity).

---

Re: digital input.... I'm not sure you really want to start thinking about that until you get your head round your current setup!


Edited by colinmono - 30 September 2010 at 4:48pm
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colinmono View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote colinmono Quote  Post ReplyReply Direct Link To This Post Posted: 29 September 2010 at 5:34pm
p.s. the name's Colin by the way, or colinmono if you prefer, not sure who this colinmonRo character is, perhaps my glamorous alter ego LOL
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Pirlo Quote  Post ReplyReply Direct Link To This Post Posted: 29 September 2010 at 11:56pm
JaKe, wich one would ya prefer (drawner or FS) and why!?
I´m searching for a 100%-secure-way to protect my stuff against the announced "enthusiastic DJ's", using a 336T as ls-management at the moment that have the same "protection-problem" then the berry (...or I´m unable to set it well, also possible, but think an additional protection could not be bad)
Ideally it should be absolutly inaudible in the signal-chain if it just "watch" and not protect.

Originally posted by JaKe JaKe wrote:

The levels on the DCX are a little confusing 0dB on the DCX is actually +22dBu.
For overall protection look at a Drawmer SP2120 or an AVC2 as the DCX limiters will not protect against over enthusiastic DJ's etc.





Edited by Pirlo - 29 September 2010 at 11:58pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jbinks Quote  Post ReplyReply Direct Link To This Post Posted: 30 September 2010 at 9:51am
Originally posted by Pirlo Pirlo wrote:

a 100%-secure-way to protect my stuff against the announced "enthusiastic DJ's"

Formula Sound AVC2
Bomb-proof.

Some people argue that they make it sound pants, but that's only after the DJ has cranked the level to (about) 22db ABOVE the limit. At that point the inputs on the AVC2 are clipping their stages and there's nothing that the unit can do about that.

I have AVC2s in every rack, they're brilliant! You simply can't "turn it up" past the level that the AVC2 is set to. If you do, it just turns it back down in sync. It has a series of red lights on the front that show it is attenuating and by how much you need to reduce the input. It also has a +10v output that you can use to drive a "reduce mixer output now, you stupid chump" light via a small relay/transistor.




As for the VU meters on the Ultradrive, I never see anything on them! Nobody does. Just ignore them! The only useful lights on the unit are the "clip" lights on the outputs. These come on at the point that you have set your limiter so you know it is affecting the output.

I did think about making some -20db pad/attenuation XLR-XLR cables at one point (one for each output) so that I could run the outputs with less/no attenuation in the DCX. That would bring the VU meters to life and make it look pretty, but I decided it was ultimately pointless and wouldn't actually achieve anything useful. It would also introduce the possibility of people playing with the cabling and swapping cables etc.
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