Re-amping is a technique that has been around for many years but it's come into use heavily over the last few years with the explosion of home recording technology. The concept is simple: I record my bass direct, thru my high end pre amps, to create a "direct" bass track. I do all of my "punches" and edits on a single track, creating a single "master" bass track. I work with it till its just right.
For most people, this is enough. The majority of recordings I have done have been with a single bass track. However, some people want more options for bass tone. The most obvious solution: create a "mic" bass sound, similar to what a live sound engineer would have in a live setting: a dry or "direct" sound and a amp of "mic" sound. How do I do this? I "re-amp" the recorded bass track.
Once the final bass track is approved, I take the pre-recorded bass signal out thru the re-amp box. The re-amp box is like a direct box in reverse. It converts the signal that I am sending from my audio interface to instrument level. This way, the signal is the same as if it came from the bass itself. I choose an amp and plug it in. When I hit "play" in Logic, what I hear is ME thru the amp. I am able to adjust the tone of the amp to get exactly the sound and add any effects, pedals, etc..... Once I have just the right tone, I put a microphone in front of the amp, get the proper level and press record. As a result, an "amp" track that synchs exactly with the "direct" sound is created. This gives you the option of two different tones for your mix. It can be very effective, especially for rock bass tones.
In the past, its been common also to simply record two bass tracks at the same time, but that creates more work..... then you have two tracks to edit. Creating the mic bass track AFTER the direct track is recorded allows me to get EXACTLY the sound that I want and record it for you. Maybe even try out a different amp? Different mics. Different placement, etc..... I think you get the idea.