The reasoning behind this is to allow for headroom. Headroom is nothing more than the difference between the loudest part of your recording and 0dB, which is where your recording will begin to clip.
For example: if I am recording spoken word, and I set my preamp gain so I'm hitting -10dB at my loudest, then my voice can unexpectedly get 10dB louder before I begin clipping/distorting, ultimately ruining the recording.
It ultimately comes down to how dynamic the sound source you're recording is. If it is a sine wave that does not change volume, you can probably set your preamp to record around -1dB or -2dB. But if you're recording an expressive singer that goes from soft singing to screaming in a single take, this can vary drastically in loudness, so you may want to set your preamp so you're hitting -10dB or even -18dB.
4. How does gain affect your sound?
There are many schools of thoughts, and arguments to be had regarding coloration of preamp on your recordings, but we're going to avoid those in this article and focus on the more noticeable impact on your recording.
- Setting your gain too high: When you set your gain too high (i.e. so you're hitting -1dB on your meter), this does not allow for any wiggle room. You have to remain consistent in your levels, and if you get excited and begin to speak loudly, your signal will exceed 0dB and clip or distort.
Once you have recorded something and it contains clipping, there is nothing that can be done to clean up that recording. You're stuck with it. So I would always suggest you err on the side of caution and record slightly quieter than you think you need.
- Setting your gain too low: This issue seems to be less pervasive online, but if you set your gain too low and you're using a subpar preamp with a high noise floor you risk losing, or mixing your signal in the noise floor.
What this means is that if your preamp has a noise floor of -50dB, and you're recording so you're peaks are hitting -30dB, you're going to run into some issues. This is caused because in post, you're going to have to boost this recording by ~30dB. This means that your noise floor is no longer -50dB, but it's been boosted so it will be -20dB. So just remember, when you're boosting your recording in post, you're not just boosting the recorded sound source, you're also boosting the noise that's introduced by your preamp.
Conclusion
I think that should give you a basic framework to work off when you're setting up your preamp/interface before recording a podcast or youtube video. Until next time, may your recordings have no clipping, a low noise floor, and contain good content. Good luck.