Reaper's ability to run multiple instances of plug-ins is impressive, but how do you keep track of them all and maintain optimum performance?
Reaper is one of the most efficient multitrack applications I've used over the years. It can run lots of instances of heavy‑duty plug‑ins and soft synths — probably more than many of its competitors — without stuttering to a halt. The default Reaper settings work well with eight‑core CPUs and beyond, typically offering over 95 percent utilisation of all cores.
To achieve this efficiency, Reaper mostly uses 'Anticipatory FX processing' that runs at irregular intervals, often out of order, and slightly ahead of time. Apparently, there are very few times when the cores need to synchronise with each other, and using this scheme, Reaper can let them all crank away using nearly all of the available CPU power. 
Reaper's 'Anticipatory FX Processing' allows it to use almost all the available CPU power, resulting in a higher maximum plug-in count than most other DAWs.
Exceptions include when you're monitoring input signals with low latency during recording, and when you're running Universal Audio UAD1 DSP cards, which both prefer a more classic 'Synchronous FX multi‑processing' scheme. If you fall into either of these categories, to achieve better performance you should do the following:
- Open Reaper's Preferences window
- Click on the topmost category, labelled 'Audio'.
- Un‑tick the 'Apply anticipative FX processing when rendering' option.
- Jump down to the Plug‑ins/VST section and tick the 'UAD1 synchronous mode' option.
The VST Plug‑ins section of the Reaper Preferences window is the key to accessing multiple folders full of plug‑ins, and to tweaking the CPU settings for use with UAD1 DSP cards.
Peak Performance
Reaper also has quite the best performance meter I've found yet in a sequencer application, offering a wide range of useful options, including total CPU use and hard drive activity, but also displaying current RAM use and remaining system memory, both of which are handy for heavy users of samples. Anyone who is about to upgrade their computer's memory should take a look at these last two, because there's absolutely no point in adding more RAM if there's still plenty available when you're running your heaviest projects! You can even see your RAM consumption drop if you disable individual plug‑in graphic interfaces in favour of a simpler generic interface, and therefore figure out which of your 'pretty' plug‑ins guzzle most RAM for their graphics.
It may only be a tiny window, but the Reaper Performance Meter really helps you monitor how close to its CPU limits your computer is running, on a track-by-track basis, and how much RAM is still available.
Even better for those who run their PCs close to the edge, the effects CPU use is separately displayed, both as a total figure and by track, so you can see exactly which plug‑ins are devouring most CPU cycles, and which track they are on. If you find you're running a little close to your processor limits on a particular project, consider rendering the most CPU‑intensive track, to reclaim its effect quota.
Easier Plug‑in Choices
Cockos supply a generous bundle of their own 'Rea' range of VST plug‑in effects with Reaper, as well as a huge collection of 'JS' plug‑ins. Did you know that the latter includes a really handy Tone Generator, which can output a sine, triangle or sawtooth wave of any frequency, and shift it very quickly and exactly to any 12‑tone note for tuning and level setup purposes? There's also a Tuner that can help to get any instrument in tune.
Unfortunately, once you've got your own plug‑ins installed as well as all the bundled ones, the full list that appears when you click on an 'Add FX' button can become very unwieldy. Nothing blunts creativity more than searching through enormous lists to find the desired instrument or plug‑in effect, so here are some tips that should make things easier.
Perfect Vision: First, make sure Reaper can see all your plug‑ins. Although it automatically creates its own Reaper\plugins folder for bundled offerings, it can also find your VST plug‑ins across multiple folders, even if located on other partitions or drives. The latter can be particularly useful if you want to install larger libraries on a different drive or partition from your operating system, to keep your backups to a more manageable size. If you want Reaper to scan additional folders, simply open the Preferences dialogue, select the Plug‑ins VST page in the left‑hand pane, then click on the 'Add' button and browse to the new path names.
Show Your Folders: Many users don't realise that you can force Reaper to display your existing VST folder structure, so if you already carefully sort your effects into multiple folders by manufacturer or genre, just click on the 'Options' drop‑down menu in the Add FX window and make sure the 'Show VST Folders' option is ticked.
Filter Options: The quickest and easiest way to narrow down your searches is Reaper's Filter option. Often missed by new users, this is a line across the bottom of the Add FX dialogue where you can type in any combination of characters contained anywhere in the plug‑in name, and it's surprisingly versatile. You can, for instance, enter a manufacturer's name to narrow down the list to only display their products ('PSP', for instance, will narrow the list to only display your PSP plug‑ins), and once you've entered a search term it remains in force until removed, so you can quickly move between instruments and plug‑ins from this manufacturer by clicking on the 'VST' or 'VSTi' categories in the left‑hand pane. Many plug‑ins indicate their genre in their name, so entering 'EQ', 'delay', 'filter', or 'stereo' will produce some relevant listings, although these won't be comprehensive, as Reaper has no way of knowing that (for instance) PSP's Xenon is a mastering limiter.
Renaming: One way to force all the relevant plug‑ins to appear during a search is to change the name of plug‑ins as displayed within Reaper, by right‑clicking on it and using the 'Rename FX' option. You could, for instance, add the letters 'EQ', 'RVB' and 'CMP' to the start of the existing names, to signify an EQ, reverb, or compressor respectively.
Sort By Type: If you want to pre‑sort your plug‑ins more thoroughly by genre, I find the best way is to right‑click on 'My Folders' in the left‑hand pane of the Add FX window and use the 'Create new folder' option for each of your proposed categories. A folder set that has worked well for me over the years includes: Dynamics, Enhancers, EQ, Reverb, Spatial, Special FX, Time Shift (chorus, echo and delays), and Tools. Once you've created your new folders, just drag existing plug‑ins into them and you can then instantly see just the contents of a specific category. 
Adding a carefully chosen set of custom folders to the My Folders area of your Add FX window like this means that you no longer need waste time searching for specific effect types.
Secret Shortcut: Here's a final effects shortcut that many Reaper users don't seem to have discovered. When you're displaying the effects window for a track, you don't even have to move your cursor over to the Add button: just double‑click anywhere in the white area where your existing effects are already displayed and the Add FX window will automatically appear. They seem to think of everything!