Last time, we talked about why we want to have proper input gain structure. Today, we’ll talk about how to actually do it. This may not be the only way to accomplish it, but I’ve had great success with this method for over 20 years.
Here’s how I approach the process.
Gain setting in the digital world
For each input channel, I would have the musician play their at their loudest level. I then dial up the input gain until I’m within about 8-12 dB of full scale (minus 8-12 dB on the meters). I like to leave a little room for the musician to play louder when the lights go up (they always do). Many digital boards also have a trim (or attenuation) control in addition to the input gain. I use my trim to dial the level back to where it should be in the mix with my faders at unity. Because I’ve gained my entire system properly, my main fader is sitting at unity as well, and all is right with the world. I am also using VCAs to manage groups of faders (drums, guitars, keys, BGVs, etc.) and those live at unity as well, at least to start. All of this ensures that my signal to noise ratio is optimized at the A/D stage (just after the mic pre), and my starting point for my mix is faders at unity.
Now, if you don’t have a digital trim control on your board, you have a decision to make. You won’t likely be able to run the mic pre’s hard without having too much signal at some point, so you’ll need to dial the level back somewhere. Of course, you can always turn the fader down, but then you lose fader resolution. A better alternative would be to use a VCA to keep your fader at zero. That can get tricky, however. Take a drum kit for example: If you optimize the gain on the kick, snare and hat, chances are, the hat will be way too loud in the mix. But more than likely, you’re using a single VCA for the entire drum kit. So now what? Well, you could break the drums up into zones and use one VCA for each; kick & snare, toms, hat & overheads might work. That way you can pull back the faders at the VCA level (a VCA is really an electronic remote control of the faders), and maintain fader resolution. You could do a similar trick with groups if you have them.
If you run short of VCAs, I would suggest breaking my rule and set the input gain up so that the fader remains around unity for a proper mix. Audio is a lot about compromise, and in this case I’ll give up absolute input S/N to gain faders at unity. I have found that to be the wiser trade, especially for things like cymbals.
Gain setting in an analog world
Really, the process is much the same, though you are much less likely to have a trim control after the gain control. In that case, the same rules apply as a digital board without a trim knob. You still want to have good input level coming into the channel (at least as much as you can), then turn it down as needed later in the mixing stage. You also want to keep your faders running around unity. Make the trades where you have to.
In either the digital or analog world, what you don’t want to do is under-drive your mic pre’s and have to add a lot of gain down the road. Sure you can push a fader up for a guitar solo, but you don’t want to regularly run your input faders at +8, your groups at +10 and your main at +5 because your input gain is set too low.
The exception to the rule
Now, all of this assumes you’re running on a professional grade mixer that has a mix structure with enough headroom. If you find yourself mixing on a Mackie or Behringer (or similar music store brand), chances are you’ll run out of headroom in your mix bus very quickly. If you set input gains on a Mackie the way you should, when all those hot signals hit the mix bus, things tend to go south quickly. The busses saturate and you lose all sense of dynamics. In that case, you need to really keep an eye on your overall output level and run input gains down accordingly. This isn’t a dig on cheap mixers—you can only expect so much for what you pay for them—it’s just reality.
That’s a quick guide to setting up your gain for an input channel. As I mentioned earlier, if you go through this whole process only to find that your overall SPL in the house system is either way too loud or way too soft, you have some work to do at the system processor or amp level. But that’s another post...
While I’ve written about gain structure before, I continue to run across people who don’t fully understand it. And that means one thing; I need to keep writing about it. I actually understand why many people have a limited understanding of proper gain structure. It’s not glamorous like plug-ins or digital consoles, and there is really nothing new to discuss. However, if you’ve never gotten a good handle on how to properly set gains on your console, there is no time like the present to learn.
If your gain structure is whack, no amount of EQ, plug-ins or compression will fix it. For this post, I will focus primarily on input channel gain structure (overall system gain structure is another post, but I’ll mention it briefly).
To Hit the Pre's Hard Or Not?
It has often been debated whether it is better to hit the pre-amps hard then turn down at the main output, or run the mains up around unity and dial back input gain to get the SPL you want out of the system. As a general rule (there is an exception, which I’ll detail in a minute), I would argue the former is the correct (or at least better) method, and here’s why. Most pre-amps sound best when you hit them pretty hard—at least up to the point of clipping, which is too hard. By running your pre-amps hard—and by hard I mean within 6-12 dB below full-scale on a digital board, or within 6-12 dB of clipping on an analog board—you are maximizing your signal to noise ratio. Typically, preamps just sound better when you keep the levels up. Keep in mind, that’s a general rule, your mileage may vary. Now, it’s quite possible that if you dial your input gains up so that all your pre-amps are running high, your overall system level will be too high. That’s when you would lower your main level to compensate. This method will keep the signal to noise ratio high throughout the mixing chain, and will attenuate the signal at the last possible moment.
Goals of Proper Input Gain Structure
Before we get to setting up the gain structure, let me lay out my goals in for the process. First, I want to maximize S/N ratio. Keeping the input level high means I won’t be boosting it later, which adds noise. Second, I like to mix with my faders around unity. Mixing with faders at unity is another key ingredient to good mixing.
The fader resolution is highest right around unity, so you can easily make small adjustments. If you try to mix with your faders at -20, a slight change in fader position might yield a 3-5 dB change rather than the 1-2 you actually desire. Finally, I want to be sending a very solid signal out of my mixer to the processors to again maximize signal to noise.
Using All the Bits?
At one point, I believed that if we were mixing in the digital world, we wanted to try to use up as many bits as possible to keep S/N high. And that may have been true at one point, but now that even inexpensive consoles are using 24, 36, 40 and higher floating point resolution internally, we effectively have unlimited dynamic range and high S/N ratios. Modern digital consoles are very quiet and have great dynamic range. So the point of running the input gain high is really to extract the best tone out of the pre’s.
So now that we have some understanding of the goals of the process, we need to consider how to properly set up the gain on the console. And that will be the focus of the next post.
Today's post is brought to you by Pacific Coast Entertainment. Pacific Coast Entertainment is the premier event production company servicing Southern California and the western states. PCE offers a complete line of Lighting, Audio, Video, and Staging equipment for rentals, sales and installs. Where old fashion customer service meets high tech solutions. PCE, your one stop tech resource.
There are some conversations that I have over and over. Of late, conversations about building a new building have been popping back up. Of course, hundreds of things need to be considered when building a new building, but there are few themes that seem to get missed more often that not. Skipping these things ensures two things: First, you and your congregation will not be happy with the performance of the sound, lighting and/or video in the room. Second, there will remain a healthy market for companies that specialize in fixing churches that were designed and built poorly.
With that said, here are three things you cannot skimp on when entering a building project.
Fix the Acoustics Before You Build
First, the overall acoustic signature of the room has to be correct. This is where most churches take short cuts. They let the architect design the building; which is fine except most architects really don’t understand how acoustics work. Now that I work with architects, I understand why. They don’t look at buildings the same way we do as production folks. A few are getting better at it, but they're the ones who design churches for a living and have AVL guys on staff.
The problem is most architects want the room to look nice and be easy to build. They never consider standing waves, comb filtering, reverberation time, reflections, and other nasty acoustical anomalies that will make it hard to get decent sound. Some argue that it can be fixed with electronics. It can't. There is no magic black box that will suddenly cancel out the bounce off the back wall that makes it really hard for everyone in the room to hear what the pastor is saying.
So I strongly suggest all churches have an acoustician look at the plans before they are finalized. Most of the time, it only takes a few tweaks here and there to make a huge difference in how intelligible the room will be, and most of the time the cost to build is the same or only marginally higher. Very few churches get this part right, and it's why there's a huge market for acoustical study and retrofit of existing buildings. Given the acoustic treatment budgets in some of our remodel projects, I can guarantee you it’s a lot more expensive to fix it later.
Don’t Skimp on Infrastructure
The second thing to consider is infrastructure. Again, most churches don't think of this. Audio, video, and lighting take a lot of wiring. If you leave it to the electrician to do it, you will be fighting the building forever. Especially if you are on a concrete slab. You need an easy way to get cabling from the tech booth to the stage; to speakers, to video projectors and to the dimmers. That means conduit. Conduit is cheap and easy to put in as the shell is going up. Afterward, not so much. Once you determine your needs for right now, lay out the conduits you need and make double-dog sure they get put in. Then add a few more empties just in case. And go big on the empties. Nothing is quite as frustrating as trying to figure out how to get a VGA cable down a 3/4" conduit (unless you enjoy making up Mini-15 connectors...). Having a couple of empty 2" conduits will make your life (or someone who comes after you) a lot easier in a year or three.
Get Your Systems Integrator Involved Early
The final thing (well, I could think of a dozen more, but these are the biggies) is to get your A/V/L systems integrator involved in the project now. Again, most churches wait until the building is up and drywall is being taped before considering who they'll use for the A/V. Bad idea. As with the acoustician, the earlier you get the A/V guys involved, the easier, cheaper and better the final product will be. They will be able to tell you what kind of wire to have pulled while the building is open. They can work with the acoustician to get the speaker fly points set correctly. They will be on the watch to make sure a duct run doesn't end up where you need to put a screen or projector.
Choose your vendors carefully of course; make sure they have a proven track record of getting church design & install correct. Don't skimp on the design and planning phase. Cut out equipment if you have to. You can always re-purpose your existing mixer and upgrade to digital later. It's a lot harder to acoustically retrofit a poorly designed building. It's better to start with just a few lights and add as you go than to be fighting too low of a trim height because the building wasn't designed properly.
There is a lot to do when starting a building project. Sadly, the systems that churches rely on every single week to create powerful and engaging worship experiences are often afterthoughts at best. Don’t make that mistake. Your congregation will thank you later.