Since I can't make a video with sound here in work (and I don't have a lot of drum tracks handy) I decided to throw together a quick screenshot tutorial. Click on the thumbnails for full resolution shots.
First, I've uploaded a .zip file which has the same tracks FORBIDDEN uploaded above (cheers dude!). Since we were focusing on the start of the track, I've chopped out everything else and just left the start there. The Reaper project file is "DrumEdit Test.RPP". There's also a second Reaper project in the .zip file, "DrumEdit Test Corrected.RPP" which shows what it's like corrected.
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GRAB THE ZIP! (33MB) <---
1. Unzip "example_1.zip" and open the "DrumEdit Test.RPP" project. It should look like it does below. Notice how the kick and snare tracks do not align to the grid.
2. Select all (CTRL-A) and group the drum tracks (G).
3. First we're going to quantize to the snare. Click near the start of the snare-top track and hit TAB on your keyboard (TAB to transient). This will snap us to each transient. Hit 'S' on your keyboard to split all of the grouped tracks at this point.
4. Click on the snare track again so that it's the only track/item selected, we don't want to tab to transients on other tracks. TAB and split for all of the remaining transients. You'll have to select each item after a split to TAB to the next transient. When complete, select all (CTRL-A) and it should look like this:
5. Right click on any item and select "Item processing -> Quantize item positions to grid..."
6. Check the 3rd box down, "Shorten earlier items..." and set its value to 0.
7. Now right click on any item and select "Item processing -> Quantize item positions to grid..." again. This time select both the 2nd and 3rd check-boxes and set their values to 10.
8. Our snare is now quantized, but our kick is not.
9. I like to increase the grid resolution when quantizing the kick. Right click on the "Grid lines visible..." button highlighted here in red and set the line spacing to 1/2.
10. Split the kick in the same manner that we split the snare (TAB and 'S' - the increased grid spacing helps here).
You should have something the resembles the following:
11. Repeat steps 6 and 7 to quantize the tracks again.
12. Select all items, right click and select "Glue selected items".
13. Our corrected track should now look like it does below.
If anyone's got any suggestions for improvement, I'd love to hear them!