We recorded an electric guitar using Protools yesterday. Its interesting that while there are a few principles there are really no rules and its worth trying different mics and positions to see what you like. Which microphone sounds best might also depend on the room.
Try to make sure you have a good guitar, amp and guitarist!. The position of the microphone should be quite close to the amp to record with greatest accuracy and to minimize any sound from the room. The mic should be pointed at a 90 degree angle to the grill. It could be placed dead centre to the speaker or it could be moved towards the outer rim. Apparently this increases the bass and gives a warmer sound than pointing directly to the centre of the speaker.
We used two mics yesterday. A dynamic mic in the centre of the amp speaker, pretty much against the speaker cloth. We then added a condenser mic about two feet from the amp (with the - 10 dcb button on so as not to pick up extraneous sounds from the room). We recorded onto two tracks through Protools and it sounded good.
Next task is to research how to record other guitars. So what would be the best way to record an bass or an acoustic guitar?
Recording Bass Guitar
Like any other guitar its good to have a good guitar, well set up and good amp. You might be able to record directly into a mixing desk. From the reading I have done you might be able to record direct (DI) either through an interface or into a DI Box.
But many engineers prefer recording with a microphone or a mixture of both.
Dynamic or condenser mics? A good choice might be a large diaphragm but Dynamic miss will give good results too. Whatever the choice, the mic needs to be good at responding to low end bass. The rules are similar to recording electric guitar. Place the mic at the centre of the speaker for a bright sound and at the edge for a more mellow sound.
Compression might be necessary - although one advantage of recording from speakers is that same compression will have been dealt with naturally as part of the amplification.
Recording Acoustic Guitars
There are lots of YouTube videos on various layouts of mics that you can try. An interesting article at http://www.humbuckermusic.com/acguitrectec.html gives three techniques for stereo miking. Helpfully it recognises that if you ask five different engineers you will get five different answers but concludes that stereo miking is really the best method. So how do you do it?
First, the Spaced Pair. Here there are two mics placed with one pointing to around the 12th fret and one to the bridge.
The second technique is a variation of the spaced pair but this time with a mic pointed at the 12th fret of the guitar and the second mic by the players ear above the bridge. You can play around with the positions a bit which can make quite a difference.
Apparently this gives a slightly thinner sound than the previous set up. With both of these you should also remember the 3 in 1 rule (getting technical here) which apparently means that you should keep the mics apart three times the distance that you place them from the guitar.