If you don’t have yet any drum samples, start with this
http://www.analoguedrums.com/details-bm.php
Start with easy song. So not anything with complicate snare rolls or ghost notes...
In Reaper duplicate the snare track. And add these plugins to that duplicate track
1. JS: Turn audio signal into velocity-sensitive drum trigger
With proper settings this will give you midi pulse everytime the snare is hit. You'll see a red line pulse in mixers meter if it's working
2. JS: MIDI velocity control
The first plugin gives quite weak midi signal. Add something like 30-60 to it, and you’ll have good stronger midi pulse.
3. ReaSamplOmatic500
This will play chosen drum sound everytime there is midi pulse.
If you downloaded those big mono samples, then you’ll have a nice velocity layered snare samples. Import them into it. You can also use what ever single snare sample. And if you happen to find some nice clean drum sounds from some multitracks, you can easily create your own samples from them.
Same with kick...
The reason why I asked you to duplicate the original snare track is: you can play the original snare in your left ear and sample in your right ear. That's easy way to check if the trigger detects correctly each snare hit. And of course quite often you can also the original track in mix and just give some lacking flavour from samples.
Be prepared to study those trigger settings. They make big difference. Sometimes you can add eq or compressior before trigger, to make the detecting process easier (or more difficult)
When you’re ready with your settings, it’s not bad idea to ”freeze” those tracks, ie turn them into normal wav-tracks and turn off the trigger track. Check afterwards that alignment is still ok. Sometimes there’s some movement.
If other's have more Reaper trigger tricks, I'm all ears. I'm new to Reaper, and I'm just stumbling in the learning process...
Or any tips to good free or cheap samples