“Gain staging" (aka "gain structuring") sounds more complicated than it is. It simply means optimizing levels to get the desired performance from your gear or software. Generally speaking, the idea is to set levels that provide maximum signal-to-noise ratio without clipping. However, as you'll see in this excerpt from Start to Finish: Jacquire King - Episode 3 - Setting Up The Vocal Chain And Rhythm Guitar, there are sometimes gear-specific reasons for setting particular levels.
Balancing Act
We pick up the action with Jacquire getting set for a vocal session for the band Oak and Ash at Flux Studios in New York City. After the mic, the vocal chain includes a Past/Neve 31102 mic preamp with EQ and a vintage Teletronix LA-2A leveling amp, arguably the most sought-after optical compressor, particularly for vocals.
The signal from the vocal mic goes from the Neve preamp to the Teletronix LA-2A before going into Pro Tools.
As the singer runs through his vocal part, we see Jacquire setting levels on both devices. One of the adjustments he makes is to turn down the preamp's output going to the compressor.
He’s doing that to create headroom so he can increase the input level coming from the mic. "I like the sound of a Neve module when you're kind of pushing it just a little bit," Jacquire says. "The LA-2A has a wonderful sound to it. It's managing the tone that I'm putting into it. It affects the tone, but the Neve module and the way I set it is even more critical. So when I lower the output, it allows me to turn the input gain up."
The preamp sounds good with an overloaded input, but he's keeping the output level from being too hot for two reasons: One is to avoid distortion at the output stage, and the other is to prevent hitting the input of the LA-2A too hard. Like many compressors, the LA-2A attenuates more as its input level increases.
Peak-a-Boo
Another way Jacquire compensates when the compression gets too heavy is to turn down the LA-2A's Peak Reduction knob. It's like a threshold setting on a standard compressor.
When you're recording a vocal, you typically should go light on the compression. You can always add more when mixing, but you can't reduce the compression you've recorded to a track.
Jacquire adjusts the Peak Reduction knob on the LA-2A to change the compression amount.
Gain, the other knob on the LA-2A, is a makeup gain to compensate for the compressor's attenuation. It's also the last level control before the signal hits the recorder, so Jacquire has to make sure it's not too loud, or clipping will occur going into Pro Tools' digital input. Unlike when you overload analog inputs, which can give you sweet saturation, sending too much level into a digital input when recording clips the signal and creates unpleasant distortion.
When dealing with more than one component (whether hardware- or plug-in-based), level-setting will require more care. Not only that, you need to know the gear well enough to understand how different levels will affect the performance of a given component.
For instance, if you weren't aware that the Neve preamp was capable of pleasant saturation when the input level is high, you might set more conventional levels and not get as good a result. Or, if you didn't realize that the input of the LA-2A provides more compression the harder you hit it, you might wonder why the gain reduction is varying so much as you adjust the preamp output feeding it.
Clip Clop
When you're working with plug-ins, you have to be careful not to overload the output, because that can cause nasty-sounding digital clipping. Many plug-ins, particularly analog-modeled ones, are designed to let you create saturation by overloading the input. But on the output side, a lot of them will clip if you push them too hard.
There are some analog modeled plug-ins designed to let you overload the output without causing digital clipping. But as general rule, when you're sending hot levels into a preamp plug-in to overdrive it, you can avoid clipping at the output simply by lowering the output control. Use your ears as the final judge. Also remember that if you have another plug-in after the one that’s overloading, it’s input will get overloaded unless you either A) turn down the output of the first plug-in, or B) turn down the input of the second.
To avoid digital clipping, be careful about overloading a plug-in’s output.
The Many Stages of Gain
In the excerpt, we saw how Jacquire used saturation of the outboard Neve preamp and compression from the LA-2A to create a richer vocal sound for a tracking session. When mixing, you end up doing a lot of plug-in gain staging. If you know how your plug-ins react to different input and output levels you can get more out of their tone shaping capabilities.
Here's an example. This DI guitar track is going through an amp modeler (Scuffham S-Gear) and then into a Waves CLA Mix Hub channel strip. The preamp section of the latter is designed to react like an analog preamp and give you analog-like saturation if you overload it. Like with any plug-in, you have to be careful of overloading the output.
First, here's the guitar with a moderate input setting on CLA Mix Hub. The output level control is at its default of 0dB.
This time, the preamp is set to the much hotter Mic range. Because of the gain increase on the input, the output had to be reduced to -18dB to keep it from overloading. But the difference in saturation is quite evident. (Note that we level-matched both examples to avoid the "louder is better" syndrome).
In the example a high input-gain setting drove Waves CLA Mix Hub into analog saturation.
Whether you’re using a hardware or plug-in compressor, you have to be conscious of how hard you're hitting it’s input. Generally speaking, the higher the input level you feed it, the more compression you'll get.
In the following examples, which were also level-matched after the fact, you'll hear a drum kit going through a UAD Helios Type 69 preamp into a UAD TubeTech CL 1B compressor plug-in. The first time through, the Helios' output fader is about -8dB, and that creates roughly -2dB of gain reduction in the CL 1B, which has no input control.
This time, the output fader is set to just below 0dB, which drives the compressor harder, creating gain reduction peaking at around 5dB.
In the second drum example, a higher output setting on the UAD Helios Type 69 preamp plug-in created more gain reduction in UAD TubeTech CL 1B compressor.
As you can see from the excerpt and these examples, input levels can impact the behavior of a processor pretty significantly, and output levels are something you always have to pay attention to. Here we were dealing with a single track. Once you start to gain stage an entire mix and have to get optimal levels on tracks, sub-busses and the master bus—not to mention all your plug-ins—many other factors come into play. We don't have space to get into that here, but it's likely to be covered in a future blog entry.