New DBX 2231 - Gain Structure

[Kevin Mc Carthy]

I used my new DBX 2231 for the first time tonight at band practice. The manual is not real helpful. If I adjust the output of my mixer to the level that we want to play at (vocals only), I only get the first light on the output meter lighting up (-10). Is that right/OK? Also, When will I know to adjust the input gain? I have it set at 0 now. I'm thinking that I'll only need to lower it if I see the clip light come on. Will I likely ever need to raise the output gain if I'm using the EQ in proper moderation? I really haven't had that much time to play with it yet but I sure would like some input on these questions.

 

Thanks!

[where02190]

Typically output gains on eq's are left at 0. Unless you'd done a ton of cutting, so the sum of the individual eq bands is a big negative number, inwhich case you might add a few db of makeup gain, but it's better to keep your nominal average across the eq at 0.

[Brad Harris]

I use the 2231's quite often for monitors, and usually, for vocal wedges (with just vocals), just the -10 led lights up (there are exceptions).

[agedhorse]

That's fine. I just tested one (the 1200 series which uses the same PCB set) and it's unity gain +/- filter contribution.

 

The -10 indication indicates that you have plenty of system headroom. If you wanted to reduce system noise a bit, you could reduce your amp sensitivity bu a few dB and increase your board level by a corresponding amount without risking overloading of your drive electronics. I assume you have a similar reading on your console output meter unless you have a lot of eq cut going on.

[DunedinDoug]

 

Originally posted by agedhorse If you wanted to reduce system noise a bit, you could reduce your amp sensitivity bu a few dB and increase your board level by a corresponding amount without risking overloading of your drive electronics. I assume you have a similar reading on your console output meter unless you have a lot of eq cut going on.

 

 

Not to hijack a thread, but I was hoping to find some information on just this topic today.

 

I have done as you suggested. In layman's terms, I "turned the mixer up and the amps down". My volume hasn't changed, but this arrangement just makes more sense.

[dboomer]

 

Originally posted by DunedinDoug I have done as you suggested. In layman's terms, I "turned the mixer up and the amps down". My volume hasn't changed, but this arrangement just makes more sense.

 

 

It does make more sense ... UNTIL ... you clip the mixer ... not "if" - UNTIL! Textbook is one thing but live sound is another.

 

The trade off (as always) in a system is noise vs distortion.

 

In an all digital system or if you were only/always playing back CDs where you could absolutely be certain of your peak levels this would be easy. In live sound with a band this is MUCH harder.

 

Clip lights in mixers do not detect clipping ... they only indicate that a certain voltage (for a length of time) has been reached.. So if you set your trim by using PFL and see no clip light on the input but then boosted your EQ or inserted a device that provided gain (now raising the level to/past clipping) but then you turn down the channel fader and the master out ... you will not receive an indication on any clip light that you are now having clipping.

 

This is why you would be better off to have a little more noise in the system to prevent you from sending that clipping down to be amplified. Do you hear any hiss that really bothers you? Do you hear it while the system is cranked? No? Then leave it backed off. This would be different in the control room of a studio ... but this is live sound.

[agedhorse]

If you are consistently operating around -10dBu and the drive electronics clip at around +20dBu, then you have 30dB of DRIVE ELECTRONICS headroom and reducing 6dBu of amp sensitivity you still have adequate headroom (assuming the amps now clip at +4dBU plus 6dBu) of 10dBu before clipping and (10dBu + 10dBu) = 20dBu of operating conditions headroom.

 

What you don't want is clipping of the drive electronics without 10dBu of compliance in the amplifier's built in limiters.

[dboomer]

He said the "output metering" was around -10. That still means nothing in terms of clipping an individual channel (or bunch of channels).

 

I'm willing to bet that with most mixers you can turn the trim all the way up and the channel fader all the way down ... talk into a mic, then bring up the fader a bit till you hear the mic (I'm sure you can hear it's clipped) but there will be no channel clip light (and none on the master out if it's turned down low) on an awful lot of mixers held in high regard by members of this board. BTW ... this won't happen with a Peavey mixer

 

More experienced users know about this, beginners probably don't so while what works for you Andy won't necessarily work for everyone.

[agedhorse]

True, it's a possibility, though looking at the drive side, there appears to be significant extra headroom between the board output (assuming it's the board meters) and the EQ output and the amp input. It's independant of whatever is happening at the board input, though I know what you mean.

[gspointer]

I am a little curious as to the peak light. it is after the insert and e.q. How can it not detect a clip from the trim knob or an inserted device? I can see if it is too quick, but a consistent signal would have too light it up right? BTW I leave each channel fader off use trim to light up the peak led and back it off a few db's.

[dboomer]

The problem is that some manufacturers only use one pick up point to sample for clipping. If they pick it up right after the mic pre then anything you do after the mic pre like boosting an EQ or adding gain with the channel fader won't be picked up. If they pick it up only after the EQ then you could clip the mic pre but cut the EQ and not flash the clip light (you'd actually have clipping but no indication). Other manufacturers pick it up after the channel fader ... same way, you could clip the mic pre, EQ or both but by turning down the slider you'd again have clipping but no clip light indicator. At Peavey we sample it at all three places. Anyplace that can have gain gets sampled. We also sample summing busses and outputs (subgroups and auxes to on our bigger boards). On a Peavey board ... if you've exceed the max voltage in any stage you'll see a clip light. On most other boards you can be clipping and never know about it.

 

To see what your board does (and I think you'll be shocked) is download the block diagram for your mixer from the website. Now find the channel clip lighton the block diagram. How many lines come out of it and go back to the channel strip? Usually it's only one time. If it's not three times it's very likely that you'll overload a channel and never get an indication. Then when you burn out a speaker with a "not too big" amp and only turned up halfway (which means nothing) you'll complain about manufacturer's specs.

[gspointer]

yep, one time post eq, pre d/o, fader buss assignment

[where02190]

 

It does make more sense ... UNTIL ... you clip the mixer ... not "if" - UNTIL! Textbook is one thing but live sound is another.

 

 

Bull{censored}. A good engineer knows proper gain staging and will ahve more than adequate headroom before clipping. I regularly turn amps down to allow me to drive consoles in their sweetspots, it is a very common practice. It also reduces system noise dramatically.

[dboomer]

What is a console's "sweetspot"?

 

An experienced mixer certainly does better than a newbie ... but let me get this straight ... you've NEVER clipped a console? No matter what? You are always able to maintain a 20dB plus amount of headroom no matter what and still turn down the gains in the amps?

[agedhorse]

Don't feel bad Don, neither Jim nor myself have figured out the sweet spot either. You might ask Max if he's familiar with the concept. I also asked an aquaintance of mine who was the lead guy on the earlier Yamaha PM series consoles and he also didn't know about it. I've designed several consoles without a grasp of this... shiver me timbers matey...

[rxnet]

sweet spot=

 

a place only i may go

a place you'll never know

a place where there's no pain

a constant 20db of gain

 

a place where I call home

a place you'll never roam

a place for me and my rack

once there you'll never go back

 

a place of audible ms delay

a place you'll never play

a place that brings me to tears

its my rack...and my twenty years!!

[agedhorse]

ROTFLMAO!

[where02190]

Any console sounds better and has a better s/n ratio if it's run at a nominal level around 0 than if the outputs are barely hitting -20 or so. I regularly turn amps down if I cannot run the board at a nominal 0 level. Better S/N, better quality of audio, lower noise floor.

 

And no I don't clip consoles. If the sytem doesn't have adequate power, I simply make due, a clipping the console isn't going to gain me any volume, just make it sound like {censored}.

 

Aged, I find it very disturbing that you of all people persist on the argument that there makes no difference where the console is run. Any seasoned veteran, of which it seems you should be, understands this concept. It is a basic principle of proper gain staging.

 

I really have no interest in opening this pissing contest again, but do you really think that running the console outputs nominal at -20 sounds the same as if they are nominal 0 and the amps turned back relative?

[agedhorse]

That's not what I said...

 

There WILL be a higher noise level if the gain structure is off by 20dB down from from "nominal", that would equate to 42-46 dB of headroom before clipping the console outputs... clearly excessive, but if the noise floor is adequately low, the sound should not be any different other than the noise floor being higher than possible.

 

Taking this to extreme of course, say go another 20db down from -20 and the noise floor will probably get in the way of the mix and become a distracting issue. At really low levels, (with enough make-up gain after the console) it's possible to get a grainy sound that appears to be a combination of noise and non-linearities due to operating at the extreme of the transfer function curve.

 

Of course, when you are mixing, even for recording and fade the audio out, you transition through this reigon anyway but without make-up gain the level of these artifacts fall proportionally and they are not heard.

 

Being off of nominal by 6dB or 10dB isn't going to make a difference, provided noise floor is sufficient.

[where02190]

 

Being off of nominal by 6dB or 10dB isn't going to make a difference, provided noise floor is sufficient.

 

 

While this won't make a difference in the noise floor draumatically, IMHO it will make a difference in the response of the console and quality of the audio. YMMV.

[dboomer]

 

Originally posted by agedhorse That's not what I said... There WILL be a higher noise level if the gain structure is off by 20dB down from from "nominal", that would equate to 42-46 dB of headroom before clipping the console outputs... clearly excessive, but if the noise floor is adequately low, the sound should not be any different other than the noise floor being higher than possible.

 

 

Yes!!

 

The only time a console should have a "sound" is when it's being used beyond it's capability. That's not to say that some coloration isn't good for the performance ... but that would still be a distortion of the sound.

 

There would definately be a "sound" associated with the loudness (including some distortion or lack of) of the system ... Fletcher -Munson and all that has nothing to do with the mixer.