Setting limiter on digital mixers.

[WalkerRichmondRanger]

I don't know if this is more mixer related or amp related, but here goes...

So I did all the math today and figured I needed to limit my Wedgehorns at around -8db, or so I thought.

I'm running an Behringer X32 Rack through an iNuke NU4-6000 4-channel amp. It thought it was 300W/ch, but when I actually measured it, it was reading 61.7V with no load and running 1k test tone at 0db.

Soo.......got me thinking. What is 0db on a digital mixer? The max output is 21db on the XLR's. So 0db is more like +21db? So instead of limiting to -9.8db's (calculated on the new voltage reading), I had to limit to -29.5db to get down to an appropriate 20V for the Wedgehorn. Does that make sense? All the stuff I read seems written for the analog world. How does it apply to digital when all the metering is different? I've read 0db analog = -18db digital. But is that it?

[Bruce Weldy]

So I did all the math today and figured I needed to limit my Wedgehorns at around -8db, or so I thought.

Limiters are set with a volt meter, not math.

[Grant Bunter]

Surely there is a meter of some description on the X32 rack.

So flick back and forth, setting slider and gain adjustment at unity gain.
ie "slider" on 0, adjust gain until you get 0db on the X32 meter.
Then adjust master sliders/output to 0dB.

Sine wave is good, however, I would be more inclined to set the limiter with a lower Hz value, as that is where the most driver excursion occurs.
So on the subs output channel, 50 or 60Hz, and tops, say 100Hz.

Adjust limiting.

Then play music.
You should then be able to run your "slider" higher, up to +10db and only flicker the limiter due to the more dynamic nature of music.
If that's not going quite right, you need to revisit your structure a little.

But Bruce is right. Kinda forget the theory, read the volts with a volt meter...

[WalkerRichmondRanger]

So just to be ready to gig these on Saturday, I just cranked it all the way up to full clip on the mixer and lowered the amp attenuator until it read 20V on the output. (halfway down and two more detents)

I'm still intrigued by the math behind it all, but I'm so steeped in theory that I won't set the attenuators and cover them with gaffer's tape so they can't be fiddled with.


I think the limiters on the X32 Rack are probably just not designed to do brick-wall limiting. Limiting at -29db just doesn't seem right. There's a bunch of other settings that may alter its behavior, though. Peak vs. RMS sensing, Log vs Linear response. I just need to get a Driverack.

[Bruce Weldy]

If you are talking about limiting your monitors, don't waste the time. You'll know if they are hitting the wall just by listening to 'em. When they start to distort and sound like crap - turn 'em down.

[dswpro]

You can use the limiters on the X32 outputs if you want. Set the attack time to zero, use PEAK detection, LOG mode, hold time to 250 ms or greater, POST EQ, key source = self. Lower the threshold while measuring your amp output to get the proper voltage limit. With real life wedge horns you should get nowhere near your limit without tearing someone's face off, or feeding back. I would also set a hi pass filter so no program material is sent to the monitors below 100 Hz.

With respect to 0db / 0 VU on a digital mixer, it is the arbitrary internal level where the outputs produce the nominal (+4db) signal. It is also somewhere below the internal digital maximum level of the mixer, which is what gives you "headroom" (not clipping above zero VU on your meters ) how far below depends on how the gain stages are set internally, the bit depth of the mixer, floating point vs fix point data, and it's input/ output stages (A/D D/A converters).