why is there a possibility to record, in stereo from the linein, what can be recorded in "real stereo" or whatever that is...?
Because you couldn't use a mono input to record to your PC from a cassette deck, or a CD-player. Because no one would buy one if it could only recoodr a single mono audio track at a time. Because outputs from synths and drum machines are usually in stereo -- the stereo mixing has already occured on the device.
Let me say a little more about stereo. Stereo is simply an attempt to capture -- and reproduce -- something like what happens when you (with your two ears) hear sounds occuring in space. The differences between what enters your left ear and what enters your right ear is what allows your brain to spatialize and tell what direction the sound is coming from. Stereo recording attempts to capture sound in a similar way, so that the differences between what's coming out of the speakers causes the apparent localization of sounds in the space between and in front of the speakers.
Sounds can be recorded in many ways. Let's say there are two basic approaches --
- capturing the accurate clear sound of each element separately and using craft and skill and art to control and simulate the spaciousness. The spatialization is achieved in the mixing phase by panning and by using stereo effects like reverb,delay, etc. that give some simulation of the multiple small echoes that typically occur in a real environment. Or,
- making a painstaking effort to capture the exact sound that is occuring in a particular space by micing in stereo.
The disadvantage with the latter is that it is an advanced art and takes a lot more skill and experience to do correctly. Also, good -sounding acoustic spaces are required, spaces isolated from outside interference (the noise of passing planes and trucks, etc.). The musicians must all play their parts all at the same time, and the relative balance between them must all be the way you want, because once it's recorded to two tracks, it's all mixed up already. In this approach, you have to doo all the work up front, and you have to live with what youi record, or do it over -- all of it -- until you get it right.
The advantage, then, with the former approach becomes obvious with a little thought. If you can get everything recorded separately, clearly and independnet of the surroundings, and can then simulate surroundings effectively, all things are possible. The parts can be mush more easily controlled, and less rigor is necessary to pull off the actual recording. Also, the creative potential for experimenting with effects in unnatural ways opens up a whole new artistic playground
Practically, you don't have a great sounding room to work with. Your best bet is to get clean, clear, uncolored mono tracks of your parts. The singer can make fifty, a hundred takes of the vocal without all the musicans needing to play the song fifty or a hundred times. Once all the tracks are captured, you play with the panning and with effects to try to simulate a sense of space.
A standard approach might be to have the kick drum and bass guitar panned dead center (meaning each speaker gets the same amount of this sound, which gives the effect that it's located right in the center between the speakers on playback. Then Guitar A might be panned somewhere to the left, and Guitar B to the right, and the lead and background vocalists similarly, to spread out the sound a bit. Reverb, delay, and other time-based effects are very commonly used to take some of the signals and scatter them around in ways similar to what happens in a good-sounding acoustical space, and to add a simulation of nearness and farness from the listeners.
The final result of all this -- no matter which approach is taken -- is a stereo mix, that has different signals going to a pair of speakers, such that this effect of sounding real can occur. This is where the craft and art of the recording engineer all come together, and it all depends on the craft and art used during the tracking of all the parts.
(Whew... did I say I was going to talk a "little" about it? Guess I got carried away. I hope this helps clarify some of the ideas a little...)
