Certain things like guitars and dynamic microphones tend to have a very low signal strength. While other items like keyboards can produce good strong (loud) signals. Pre-amps are designed to boost low signal to a more usable level without introducing a lot of unwanted noise. (i.e. hum, hiss, background noise, and sometimes even worse.) Other processors like compressors and EQs are not intended to boost signal level. Compressors are designed to keep dynamics, (volume changes) under control and EQs are used to boost or filter certain frequencies but not whole signals.
If your problem is only a weak signal while recording, then you should be using a preamp. In fact, most folks would probably advise you to always record dry. That is to say, you should use no processed effects if you can help it. A preamp would be the exception to the rule because its aim is to keep the signal clean and pure. Other processors tend to change the signal in more noticeable ways. Once a “changed” or processed signal is recorded, it cannot be undone. You can always process later until your heart is content.
Preamps come in two flavors. Tube and solid state circuit. Tube means they actually have a tube in there just like something out of the 1950s or 60s. Your better tube preamps are known for the way they add warmth and can soften up a digital recording. They somehow add a certain sweetness or fatness to the audio, especially with vocals. Circuit board preamps try their best to emulate that “warmth” but many people argue over their success. Of course, quality doesn’t come cheap. Preamps range in price well into the thousands $$$. Most will tell you that you get what you pay for. Many home and budget project studios are probably spending $100 to $500 for a preamp. Some have XLR inputs for microphones and some have ¼" inputs. Do some Internet searches on “preamp” or “mic pre” and you’ll have lots of reading material.
I hope that cleared things up a little better than mud. Good luck with it.
Gordon
