Midi is just a controller language. You can not record audio with it. If you want a clear sound you need to get a decent microphone (I use a Sm58 for everything which is only decent but does everything ok) and a firewire interface for your computer with a mic (XLR) input. You can then use the mic running into the interface running into your computer to record. Set the mic up close to the thing you are recording, if it is an speaker then I would put it only a few inches from the speaker (having another mic that records room noise can help with smoother tone a lot). If your recording a acoustic guitar I would set it up no more than 7-8 inches from the hole or up near the neck depending on what sounds better to you.

Midi won't help you, unless you are using sample libraries and a midi keyboard to write music that is created on your computer via a synth.

You can get either a USB or Firewire interfaces but I seem to remember firewire being more reliably fast even though USB has a faster burst rate.