Microphones are tools. Some are more versatile than others. Some are better at some things than others. I'm looking for the best tool I can get for $100. Which one do you think I should buy? Some people have suggested a good crosscut saw, but others say a hammer is the way to go. So- tell us about the job, and maybe we can help you select a tool. Record what? Where? To do what with it once it's recorded?
BTW- your statement regarding preamps vs interfaces is essentially correct. A preamp raises the weak mic level signal to the stronger line level, so that it can be recorded. Not all line levels are created equal, however.
-10dBV is consumer line level, which is put out by most stereo systems. This would be the "line level" output on a CD Walkman, for instance. +4dBu is "professional" line level, what most mic preamps put out. Some pieces of equipment have a switch so that they can handle either, or separate inputs for +4 and -10. Although not always true, line inputs with RCA jacks are usually -10 and line inputs with 1/4" jacks, like a guitar cable, are usually +4. Note that what a guitar puts out is neither one. That's high impedence instrument output, sometimes called "high-Z", or "instrument level".
A computer interface is a device that first changes mic or instrument level signals into +4 line level (in other words, a preamp), converts it to a digital signal, and then transfers it to a computer, usually by USB or firewire. They usually also have line level inputs. So- an interface is basically one or more preamps with inputs for various signals, whether mic, line, or instrument level, and an analog to digital converter. It usually also has monitoring provisions, often including analog line outs for monitor speakers, a headphone output, and vu meters, or at least clip (overload) indicator lights. For relatively affordable, I like this one:
Line 6 POD Studio UX2 | 8thstreet.com | Call 1-800-878-8882 | Most Orders Ship Free!
But there are many others by M-Audio, Motu, and others.
As far as the mic goes, that entirely depends on the mission. There simply isn't one universal, all purpose mic. Mics are classified according to the electrical principles by which they operate, the size of the diaphragm, if they have one, and what polar patterns they generate- in other words, what directions do they pick up sound best in, and what happens to the sound when it's not coming from straight on? Mics are also defined by their frequency output. Do they augment or attenuate certain frequency bands, and how much? Also what is their upper and lower frequency limits, and what happens when a source exceeds those limits? Furthermore mics vary in sensitivity and some generate subtle distortion, which may be flattering to certain sounds, like airbrushing a photograph. This is called "warm" when you like it, and "muddy" when you don't. Mics can also make their own noise, called "self-noise", some more than others. Noise, unlike distortion, is always bad, and for some uses, it matters more than for others. Once we've waded through all that, price and build quality is massively variable. I can show you an omnidirectional, solid state, small diaphragm condenser mic for under $50, and another for about $3000. On paper, they look the same. It takes a lot of green paper before you really understand the difference.
But the good news is- there are lots of very usable cheap mics out there, lots more than there used to be, in the day. So tell us what you intend to record with it, and then we can start really confusing you. No matter what you need the mic for, there are dozens of options, and we all have our favorites. You'll also notice that the poster above mentioned that he thinks you are American. He is in England. For him, the choices may be very different, due to differences in availability, tariffs, and currency exchange rates. Where you live matters, and I will often make different recommendations to people, based on where they live. Your turn- more info, please.
