Plugins have become so essential that you probably use them every day. But do you really know how they work?

Plugins are such a standard part of any modern computer-based production setup that most of us probably give them very little thought. These handy add-ons can make our lives a lot easier, but that's not to say they don't sometimes cause their own problems. At this point, some of you might think there's not much to say about plugins, but a lot of people still don't understand all the ins and outs. What's the difference between a VST, a DXi, an RTAS and a LADSPA? What's a native plugin? Where do DSP cards fit in? We'll answer these questions and a whole lot more...

Most DAWs come with a perfectly usable selection of basic instruments and effects, but plugins allow us to add features to suit our needs. With thousands of plugins available, your expansion options are huge. If you buy a new sampler, soft synth or effects processor then chances are it' ll come as a plugin. Almost all plugins fall into two categories: instruments or effects but in some cases instrument plugins may also be loaded as effects in order to use their processing sections on other sound sources.

The main advantage of the plugin format is obvious: we can expand the capabilities of our software setup quickly and easily. plugin files are typically small in comparison to full programs (although this isn't always the case, especially where large sample libraries are also involved) and slot in neatly to your existing software setup meaning that everything can be controlled, sequenced and accessed through your DAW. The fact that each plugin can use its own GUI inside the host means that interfaces are perfectly tailored to each instrument and effect. The various standardized plugin formats (more of which later) mean that most hosts are capable of running the same plugins and, in theory, all well-coded plugins should run equally as well in any compatible host. It's easy to see why plugins have achieved such success when you consider the alternative approaches.

It would be possible in theory to run all your software as separate standalone applications. Software audio and MIDI routing protocols could then connect them together, acting as a virtual patch bay between modules. Needless to say, hosting everything in one app is a great deal easier to implement and to operate.

Thankfully, the downsides of plugins are minimal. The fact that you need a host to run them can barely be considered a disadvantage - it's pretty much the whole point! Many plugins such as instruments and soft synths also come as standalone applications if you do want to run them without a host, but the convenience of running everything inside your DAW is almost always preferable. One thing that could be considered a minor disadvantage of plugins is that the number of formats available can be a little confusing at times. Let's take a run through the major ones...

VST (Virtual Studio Technology) plugins were the first major standards in the consumer digital audio world. Introduced as effects in Steinberg's Cubase back in 1996, they were closely followed by VSTi instrument plugins. Given their dominance of the early audio plugin market it's no surprise that 'VST' is sometimes erroneously used as a generic term for a plugin of any format. Although VSTs are available for both Mac and PC it should be noted that the plugin files are system-specific . Windows VST plugins (with a .DLL suffix) are not interchangeable with Mac VST plugs (.VST suffix).

DirectX (DX) plugins and DXi instruments followed closely behind VSTs and were adopted by Cakewalk but never quite achieved the same level of widespread success as VSTs. OX and DXi plugins are Windows-only. The early Mac plugin market was dominated by the VST format until the introduction of Apple's own Audio Unit (AU) format. The AU format allows developers to access the Mac operating system's built-in Core Audio functionality. The other competing technology for the Mac is MAS (MOTU Audio System), which is compatible with MOTU's Digital Performer DAW. Linux equivalents include LADSPA (Linux Audio Developers Simple plugin API), DSSI (Disposable Soft Synth Interface) and the LV2 (LADSPA version 2) format.

Digidesign's Pro Tools works in a slightly different way to most other DAWs, with two distinct categories of plugin which operate in different ways. Pro Tools RTAS (Rea I lime Audio Suite) plugins use the host computer's processing power. RTAS plugins are also often referred to as 'natiVe' plugins, and native in this sense means they run on the host computer's processor. VSTs, AUs, DX plugins and all the formats we discussed in the previous section are also native.

TDM (Time Division Multiplexing) plugins, which pre-date native plugins, carry out their processing on dedicated DSP (Digital Signal Processing) chips built into Pro Tools hardware. Separate DSP chips were originally required due to the fact that computer chips couldn't handle such complex processing, but the TOM format has survived largely due to the fact that effects processing puts practically no extra strain on the computer's resources.

In practice, the difference between most of the native formats is surprisingly small. Some plugins may be more stable in one format than another (most often this is simply due to poor programming), but the majority Will look, act and importantly sound practically identical regardless of the format. Although it's becoming Increasingly common for DAWs and hosts to support multiple plugin formats, many insist on a single format meaning that most of us have a limited choice which plugin format we use. Logic users, for example, have no choice but to use Audio Units. Unfortunately, these restrictions do mean that not all plugins can run on all systems. If you're on a Mac and a plugin only comes in Windows formats, you're pretty much out of luck. However, in certain cases you may be able to get around the problem.

Generally, plugins cause very little trouble. However, there are occasions when even the most powerful computer can run out of power, so it's necessary to consider the processor and memory burden of plugins just as you would for any other software. This is particularly true when running multiple plugins simultaneously. Although your computer might exceed the software's minimum requirements, each instance of a plugin uses more CPU power and RAM. Typically, complex soft synths and effects use the most processing power (reverb effects in particular are notorious for gobbling up processing), whereas RAM IS more of an issue for sample-based virtual instruments. Keeping an eye on CPU load and RAM usage is the only solution. Most DAWs include built-in CPU and RAM use meters but any diagnostics software should do the trick if yours doesn't.

We also need to consider the possibility that effect plugins might introduce latency. Knowledge Base veterans will recall our discussion of latency way back in FM214. Latency, introduced by digital processing, results in the sound signal being delayed. When an effect plugin introduces latency to the signal, failure to resynchronize the signal with the rest of the track will result in timing inconsistencies. The detrimental effect increases with the number of effects used.

Thankfully, just about all DAWs now include latency delay compensation (sometimes called plugin delay compensation) to account for this issue.

Although plugins primarily operate in the software domain, there are occasions when a crossover between software and hardware occurs. We've already mentioned the way Pro Tools' TDM plugins use dedicated DSP chips, and the same principle is adopted by DSP effects hardware such as Universal Audio's UAD accelerator cards. plugins are still loaded up as usual in the host, but all of their processing is carried out by the DSP chips rather than your computer's CPU.

Finally, it's worth considering the fact that you don't actually even need a computer to run your plugins. Hardware plugin hosts such as SM Pro Audio's V-Machine and Muse Research's Receptor allow you to upload plugins and run them on a small dedicated unit away from your PC. The downside is that it's still a computer in the box, so stability and plugin compatibility aren't guaranteed. Whether you're in the market for a couple of freeware soft synths or thousands of pounds' worth of top-end effects, plugins are sure to be some of the most important tools at your disposal.