Every studio or enthusiast engineer/music producer is seen talking about having a good Mic preamplifier. The definition of a good Mic pre is a debatable one; I always feel that, all preamps are good that’s why they are selling. There is a character to each preamp. This character is a result of the electronic design of the preamp. (This has nothing to do with the cosmetic design of the unit.)
Preamp is the first stage of gain staging of the audio signal. Gain staging is the most important basic step. In this tutorial we will discuss the two main controls Gain & level.
This is a picture of the Universal Audio Solo/610 Tube Preamp, this has both a gain and a level control. Aren’t gain and level just two words for the same thing?
Well no. Level is how much a signal measures in volts, or how it compares to full-scale 0 dBFS once it is inside your DAW.
Gain is a change in level. Gain can be positive or negative, and if it is negative it can be referred to as attenuation.
Lets refer to the block diagram of this preamp, the Universal Audio Solo/610.
What we can see here is that the gain control determines the gain provided by the first tube, which is a 12AX7 type. The level control however merely reduces the signal level before the final output tube.
So suppose you have a singer in front of your favourite microphone. You can control the signal level going into your DAW with either the gain control, or the level control, or both. So how should you set these controls?
There are two settings that you should know. And these are…
- Gain-high/level-low
- Gain-low/level-high
I can’t give you precise values because it will depend on how loud your singer sings and the sensitivity of your microphone. But all you need to make sure either way is that you have a good strong signal level going into your DAW and that you never see a red light in the channel while you are recording.
Since this is a tube preamp, you will expect it to provide lots of lovely warmth, (which of course is a nice word we use to mean mild distortion.)
The higher the gain setting, the more the 12AX7 is pushed and the more it will distort.
With the gain control you can find a setting that gives you just the right amount of warmth you need. But suppose that you start seeing the red overload light in the channel of your DAW. That would mean clipping and horrible distortion.
But the solution is simple – turn down the level. So the gain-high/level-low combination will give you the warm sound you want.
But suppose you want a cleaner sound – as clean as this preamp can possibly provide. Easy too – turn down the gain and compensate for the lower output with the level control. This is the gain-low/level-high setting that gives maximum transparency.
Of course, there is an infinity of in-between settings you can use, but these two extreme settings of this preamp’s controls should be something you fully understand and know what to expect in terms of sound texture and warmth.
Discrete Preamp
Discrete Meaning that there are No Tubes used In the Circuit. It’s only the transistors that do the job. Transistor preamps are
normally designed for accuracy rather than warmth, and when a
transistor preamp is driven into distortion it can sound quite harsh, or very harsh when pushed to extremes. However if the sound of transistor distortion is what you want, and your preamp has both a gain and level control, then exactly the same will apply as for the tube preamp described above.
What if your preamp doesn’t have these controls?
You’re going to have to find a way of lowering the signal level after the output of your preamp. Since the output of your preamp is connected to a line input of your audio interface, you might be able to turn down the gain here. Or any other equipment that has a line input with a gain or level control might work, with all of its other controls set to a neutral position. You will have to listen carefully however to make sure that the warmth is what you want and you haven’t strayed into harsh distortion or clipping.
If you add any warmth or distortion to your signal at a point in the signal chain before you record it, you can never go back to the clean signal. Adding warmth in this way is an artistic decision that will stay with you always.
If you do not do it the right way at the first stage , you can never fix it later !
