The Hidden Digidesign Pro Tools (part 3)
This is where we really get to the fun stuff. Heres an old problem: a guy comes in with an acoustic guitar and strums a backing for a song. Fine. Then he says that he wants to add a MIDI drum track. Politely you suggest that he should have done it the other way round, or at least strummed to a click, because it is far easier to add acoustic guitar to a MIDI track than to do it the other way round and maintain some sort of rhythmic correspondence between the two. But why should the paying customer have to compromise because of these technicalities, and he might anyway want to preserve the rhythmic ebb and flow of his original acoustic meanderings. Panic not, Pro Tools can help, and heres how...
First, record the free-tempo track into Pro Tools, preferably with a clear count in. Once the recording is made, punched into, edited and whatever else it takes to achieve perfection, edit out the section before the count in and bring the rest forward in time so that it starts exactly at the beginning of the timeline. This helps everything else make sense. Now position the cursor on the first count and from the Edit menu select Identify Beat. This allows you to specify the current position of the cursor in terms of bars and beats, i.e. bar 1 beat 1, and also a meter setting can be entered. When you have done this a small triangular beat marker will appear in the timeline. Reposition the cursor so that it sits exactly on the first beat of the second bar, repeat the process and specify that this is bar 2, beat 1. By the time you do this for the third bar, Pro Tools will have anticipated the basic tempo of the track and will probably guess accurately what bar and beat you want this to be. Continue throughout the track to the end. Obviously this will take a little time, but at the end of the process what you have is a Tempo Map and any MIDI recorded into the session can be quantised according to this tempo map and be in perfect time with the original free tempo audio. You have to hear it to believe how well this can work. If the tempo varies widely then you might find that a little additional work is required. The triangular beat markers can be grabbed and slid along the timeline to make small adjustments. If the tempo varies significantly within a bar then additional markers can be added. Funnily enough the Pro Tools manual advises not to bother with all of this and record to a click in the first place. How boring.