Learn the Proper Techniques for Gain Staging

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Proper Gain Staging

[Ed. Note: One question we get a lot refers to the difference between input gain and output level. Mac does a great job of explaining when to use the Gain knob and when to use the Level (volume) fader.]

What you are referring to is called Gain Staging, and is easy enough to ascertain, with a bit of explanation here you should have the idea for life:

First, I hope you are not running the preamp of the Berry into a mic preamp of the soundcard. That would be noisy and wrong. Hopefully you are connecting the Line Level Output of the Berry mixer to the Line Level input of the soundcard. That is the correct way to do it.

Now about the Mic input Pad:

Even though it acts like a volume control, the purpose of the Pad is not to be construed to be a Volume Fader. If that were the case there would be no need for the Volume Fader down below, right?

Purpose of the input Pad is to set the gain of the mic pre input such that the mic cannot drive the preamp into clipping while at the same time allowing us to adjust the input for maximum sensitivity obtainable.

Some mixers have a clip light on each channel that is handy for adjusting the input Pad Trim. If your mixer has this LED, then the way to set the pad is to simply turn the Volume Fader all the way down and then bring up the Trim Pad until the light is just starting to blink with the loudest signal the sound to be recorded can make. (This is always a problem when other musicians are the target source, at the sound check you ask them to play the loudest or sing the loudest they can and most will not really do that for you, be aware of that. Common problem. You set the pad levels and then when the actual recording starts they will naturally sing much louder than they did all alone at the mic check. Sign of a seasoned studio veteran is when they know to give it all they can possibly give when you are setting up the mic levels. )

If you don't have the LED indicator for each channel, then you must use your ears to adjust the Trim properly.

Good starting point for the average mic would be 12 to 1 o'clock on the dial. (12 to 1 o'clock is a good position for any potentiometer in any circuit, especially if you are not sure what the pot does at the time. Most engineers will design such that the center position of the Pot is also the center area of the circuit's normal operation. A good thing to always keep in mind, and make it a habit to suspect any pots that are set to extreme settings unless there is a good reason to do so. Any knob all the way up on the pin is suspect in my studio unless that knob is on a guitar amplifier. )

Once the Mic Trim Pad is set for the mic, you shouldn't touch it again unless you detect clipping problems from the mic being driven harder than the original pad setting. This is a clipping that you may not be able to see on the graphic wave view in the sequencer, but you will be able to hear it. That's because even though the VU meter levels are below the magic 0dB clip point of digital audio, you can indeed overdrive the analog circuits in the mixer, which creates a different kind of distortion. Sounds "grainy" if not pushed real hard.

And on to setting the Faders properly:

On the mixer, which is analog, Gain Staging is accomplished by realizing that the best signal to noise ratio can be had by getting as much gain as you can closest to the mic itself.

Open up the mic's channel fader to a spot approx 65% or so of full travel, somewhere near the marked "0dB" area on the slider.

Then open up the Master Fader (Output) on the mixer just enough to get the required VU level.

Start with the software input fader at about 65% of full scale travel, or in some cases you can just peg it full up and forget about it, getting all levels at the mixer controls. This can vary depending upon the design of the soundcard, use your ears to determine if pegging the software slider adds noise, if so, turn it down a bit accordingly.

So what you are looking at on the mixer might be Mic Fader at number 8, Output fader at number 2. Numbers don't matter, just the notion that the Gainstage closest to the mic is higher than the Gainstage closest to the soundcard input.

For a good ear training experiment, try setting the controls in the opposite (Mic gain down low and output up high) and listen for the HISSSSS noise that will create, and etch it into your memory. What you hear as hiss is actually the last gain stage over amplifying the thermal noise of the components in the active gain stages before it in the mixer. We don't want the hiss, because the noise is additive in nature, just like the desired audio is. Several tracks with hissss add up to a whole lot of hiss.

Dig?

So to reiterate, set the Pad first for highest mic sensitivity without clipping internally, then bring up the Mic's fader to somewhere above the halfway point of travel, then "crack" the output or master fader just enough to get near full VU meter travel inside the target audio sequencing software.

There ya go,

--Mac

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