Gain Staging
Gain staging is the quiet discipline that keeps a whole system sounding clean, and the idea behind it is simple: at every stage you want as much signal as possible sitting above the noise, while still leaving enough room above it that sudden peaks never hit the ceiling. You set that balance once, at the input, and then protect it all the way down the chain rather than chasing it later.
To do that you need to know where "healthy" actually is. Analog gear is built around a nominal operating level. Professional equipment runs at +4 dBu, which is about 1.23 volts; consumer gear runs at -10 dBV, about 0.32 volts. That roughly 12 dB difference is why plugging a consumer output into a professional input sounds weak and noisy — you are feeding it far less than it expects. Digital systems measure everything against 0 dBFS, the converter's absolute clipping point, and to leave room for peaks the broadcast and live worlds deliberately align nominal level well below it: around -18 dBFS under the EBU R68 standard, or -20 dBFS under SMPTE RP155. That gap between your normal level and zero is your headroom, and it is what saves you when a drummer suddenly hits harder.
The two failure modes sit at opposite ends. Too little gain and you are lifting the noise floor up with the signal, so everything hisses. Too much gain and you clip — and a clipped digital peak is gone for good, with no fader anywhere able to bring it back. The practical target is to set the trim so normal program material sits around -18 dBFS with peaks comfortably short of zero, then let every stage after it pass at roughly unity so the careful level you set survives the trip.
Set gain once at the source — don't chase it downstream.