Questions on gain controls

[whamo]

Hey all, I've been working on a pro system sort of and I have a question. Right now it consists of an Altec Lansing 944a, a Stanton rm-80 mixer and a pair of kp-301's. OK, so my question is about all of the gain controls. There's a gain control on the back of the amp, on the mixer too and a trim gain on the back of the mixer. Then you have individual gains for each channel of the mixer. OK here's the QUESTION. Is there a science to dialing this all in proper? Or, do you do like I have been doing all the while and go with your ear? The instructions that came with the mixer were minimal. Mark

[DrWho]

There IS a science to the madness, but it involves lots of boring math [] I know there are others that have worked out the math before, but alas I'm not one of them.

There are a few approaches to doing it "by ear" but they're going to depend upon your application. So I'll just spill a few thoughts as they come to mind...

One approach is to maximize the gain of the system. There is nothing more annoying than running the mixer into clipping and needing more gain - especially when the amps are just coasting along. One approach I've seen is to play a CD through the system such that you've got blinking clip lights everywhere in the signal path - the idea kinda scares me cuz you'll have speakers connected to the amps and that's probably going to be freaken loud...

On the flip side, you don't want the input trims on the mixer to be so low that you can't turn them up without blowing your hair off. Not only does this mix you into a corner, but you'll probably amplify a lot of noise too - which is the other consideration. If you have noisy components in the signal path you'll want to set their levels into a region of minimum noise floor which generally means driving that device harder and "amplifying it less" further down the chain.

If you're mic'ing drums, chances are the kick is going to be the hottest channel on the input of your mixer, so you might try solo'ing that channel and bringing its levels up to the +6dB point (or just below wherever your yellow lights start flashing...it's different on every board). You will then want to set the amps and everything else downstream so that you've got more than enough output. Dial the drum channel down a notch and then everything else should generally fall into place (again, this is one of those things of making sure you have enough gain).

But ya, I usually just set everything to the "0" point on every piece of equipment and then crank the amps to 100%. You'll want to set any system EQ's and processing so that the bypass switch results in no change in volume (also usually the lowest noise floor).

One thing I often see people doing is solo'ing out every single channel during sound check and bringing the levels up to 0dB...The problem with this is that for every doubling of channels you are roughly going to increase the output by 3dB. So on a 16 channel board, you're looking at 12dB more output. Right off the bat this is going to run the mixer into the yellow...and since sound check is usually about 8dB quieter than the actual show is going to be, you're going to max out the board real quick (especially since it's quiet in the "audience" and the guitar players always turn up higher when they return to stage). I always anticipate needing another 12dB of gain (if it's available, which often it's not).

ya...them's enough ramblings for now....

[colterphoto1]

well stated Doc- one more little item to consider- when mixing pro sound, there is a tendency for 'fader creep'. This is the term I use for individual channels to be increased a little at a time during the show and the system getting louder and louder until the PA runs out of headroom, you get into clipping, etc.

So start the sound on the low side, this will give you a chance to 'dial it in' during the first few songs and avoid that soundman's nightmare- feedback. Then as the 'creep' comes into play (I think it's somewhat a result of our ears becoming accustomed to the loud sound and wanting more, or just excitiement ), look for breaks in the musical energy such as band breaks, between song chatter, acoustic numbers etc- as an opportunity to bring things back down a bit, either on individual sliders or on the master volume. This will preserve headroom and sanity.

Michael

[DrWho]

This will preserve...sanity.

lol []

Fader creep is a big issue - and since you mentioned it I'll bring up another interesting bit of trivia:

Creeping the volume through the show actually makes things sound quieter.

As you listen to certain SPL's for extended periods of time your ears will eventually go through a threshold shift, making things sound quieter. This naturally makes you want to turn things back up a bit to regain that "full live sound" - but this will trigger yet another threshold shift that will make things sound even quieter. The cycle repeats until eventually you get to a point where the sound system can't go louder and everything is nasty compressed distorted, or everyone goes deaf.

So with this in mind, the only way to get things to sound fuller and louder is to turn down the volume - which almost seems counter-intuitive. It's really hard to turn things down though because it loses that fullness and powerful sound that everyone is always shooting for - so really, the only time you can turn things down is when that instrument isn't playing. This is a rare occurrence (moreso with amateur bands) so you gotta be on your toes and take every opportunity to turn down the volume. Granted, you don't want to get carried away and have a 60dB show [] What you're trying to do is create space so that when things need to explode (musically) you have the headroom and faders up and ready to go.

The more space (or the lower the noise floor), the louder the louder parts are going to be percieved.

I recieved a comment about a show I was mixing a few weeks ago about how clear and loud everything sounded and the person wanted to know what the SPL meter was reading. So we pulled it out and it was showing 110dB, A weighted slow...normally, this kind of volume is freaken insane loud, but the particular band playing had a TON of space in the music and you could still hold a normal conversation - you didn't even need to shout [] (which is a good way to tell how loud things are if you don't have a meter). The next band to play that night didn't have any space whatsoever....basically unbearable to listen to. We pulled out the meter and it was now reading 95dB A weighted....that's still loud, but on the 'normal' side. Yet it was unbearable and you had to shout to hear each other - there was no space. A 15dB difference in output puts a huge load on the gain structure of the system...had I set the peak output of the system for the 2nd band, then the first band would have sounded like crap because everything would start compressing upstream - thus removing the space.

110dB A-weighted is freaken loud if you're listening to most any CD, so when you're trying to dial in the system to achieve that output you're going to be sitting there thinking "crap I'll never turn it up this high" - but that's because the CD is compressed music without dynamic range. There is lag on the needle of the meter, so what you're not seeing is the space in the live music versus the lack of space in the recording...the needle just doesn't fall fast enough. The CD generally sounds fine with all the compression because they put a crap load of work into making the lack of space still sound good. You rarely have the tools to do this at a live show - though I don't know why you would want to achieve that either...[] Anyways, for a frame of reference....if your system is pumping 110 A weighted, then you can expect it to be about 120dB C weighted and then add another 10dB for transients....130dB is crap load of output (especially when you're 10m from the mains)...you're talking about 140dB at one meter (if you're outside). Ya, that's a big holy crap...the system we were using that one night is capable of 142dB at one meter [H]

Anyways, the point being that dynamic range is an important goal to strive for and that threshold shifts occur as a function of time listened to certain SPL's. The more space, the less time you spend on the higher SPL's - but you still achieve the desired psychoacoustical effect.

Overcoming fader creep is the biggest hurdle in mixing, but once you get over it the mixing console suddenly becomes a musical instrument (if I may be so bold). And to tie this back into gain structure...you want to have flexibility with the faders where you have room to crank it up, but also room to turn it down. And there is good reason the 0dB mark on the fader channels only has about 1/2" to go up and like 4" to go down...you'll want to set the channel with the fader at 0, but during the show almost nothing should be that high.

[mas]

Overcoming fader creep is the biggest hurdle in mixing

Not to diminish the issue above, but I would posit another problem in smaller venues, where ITE (in the ear) monitor mix systems are not employed, that is even worse and often contributes to fader creep and which effects not only for the total volume, but of the quality of the overall sound - and that is the monitor levels.

With all of the 'ar teests' whose egos demand 'mo me' in the monitor, and who are guilty of steadily self-regulating their own instrument gain (of course their own volume knobs ONLY go UP!), the stage volume is soon overpowering the mains.

This factor alone justifies the cost of an ITE monitor rig! The first use of ITE monitors that I heard was when Steve Miller adopted them (and he also ran almost everthing via DI as well) and the stage was quiet enough that you could actually carry on a conversation on stage during a show! (of course the rest of the time he was in his Russ Berger designed remote Idaho studio hideaway hiding survival style from the left coast riff-raff.[] ) (Now, if Capitol would only release his Journey from Eden: Recall the Beginning album on CD!!!) (oh, and as long as I am on a trivia jag, Joe Wooten - Victor, Roy ('Future Man') and Reggies's brother, has been playing keyboards with Steve since about 1990-91...man, time flies!)

Its a shame more gear isn't equipped only with remote gain control.[]

[whamo]

Thanx guys, I'll have to go over this several times. Mark

[DrWho]

lol Mark!

One thing I've been thinking about is putting voltage regulators on the electrical outlets the guitar players plug their amps into...if they're too loud, just drop the voltage to their equipment. Eventually it's gotta get quieter [][] Sadly this doesn't do anything for the drummer [6]