A Simple Test to Check Your Microphone Pre-Amp Performance
As long as your preamp is of professional quality and working properly, there is nothing about it that will prevent you from making good recordings. Preamps really don’t matter anywhere near as much as many popular recording myths suggest. Your speakers are important, the acoustics of your room are important, your microphone selection and positioning are important, and your skills and are important. The microphone preamp usually comes after all of that in order of importance. But still, you might have concerns about your preamp, and one of them is noise.
The correct way to set preamp gain is to increase it to whatever value that is necessary to achieve a good strong reading on the meters of your recording system, without clipping or distortion. But you may find that when you do this, there is a lot of background noise. This may be the acoustic background noise that is present in the room. Raising the gain of the preamp does raise this, but only in proportion to the signal you want to record. So the signal-to-noise ratio from this source of noise stays constant. But it might also be that the noise generated by the preamp itself increases. This should not happen. In fact, many preamp manufacturers quote their noise levels measured at maximum gain, because this is where the signal-to-noise ratio is greatest.
So here is a simple test…
1. Set up a microphone up in a quiet room and set the gain on your preamp to maximum. Make a recording of the background noise of the room. Now save it as recording #1
2. Lower the gain of the preamp by 20 dB. Make another recording. Save that as recording #2.
3. Normalize both recordings in your digital audio workstation so that they are the same level.
Now, there are three possibilities…
* If the noise levels are about the same. In this case you can stop worrying and get back to recording.
* Recording #2 is noisier than Recording #1. This is normal. As above, stop worrying.
* Recording #1 is noisier than Recording #2. This is a distinct warning sign that something is wrong with your preamp. This simply should not happen. Perhaps it may be time to look into a better quality pre amp or the unit you have may need repair or calibration.
Of course, I have only discussed pre amp noise level at high gain settings. But at least in this simple test, it is possible to see whether if your preamp is working properly.