Any electric or amplified instrument can be used with effects, but for the guitar they're not just an optionâ€”they're a staple. Naturally, every guitarist's preferences are different when it comes to effects, but with the flexibility of today's desktop and rack-mount guitar effects units, your own personalized sound profile can be created all in one piece of hardware. Among the many talents of an effects processor is the ability to replicate the audio characteristics of specific amplifiers and speaker cabinets, making it possible to emulate much-sought-after vintage gear without having to break the bank to get your hands on the real thing. Depending on the model, you can also mix in pre-recorded rhythm and bass or even audio from your portable music player, a feature you'll probably take great advantage of if you play solo gigs. Many units also include USB connectivity for updating their effects libraries or streaming music digitally to your studio recording software. No matter how you use them, these effects units come in many shapes and sizes, so there's one for any application. The smallest units are compact enough to fit in your hand, which makes them a good choice for times that you want to just grab and go. An ultra-portable effects unit is just the thing for an impromptu practice or jam session. For your basic home studio or permanent practice space, a bigger desktop effects unit gives up a little bit of that portability in exchange for a wider selection of features. Use your effects processor as a standalone preamp connected directly to your mixer or speaker system, or chain it to an external preamp to mix its effects with the tone and character of your favorite amp. The largest units are rack-mounted, perfect for integrating into a touring setup or the equipment rack of an enthusiast or professional studio. Generally speaking, rack units will have the biggest selection of features with the most presets and effects pre-installed as well as the most plugs and jacks to connect to other equipment. Rack-mount effects processors are all-out units for permanent or semi-permanent installations. When making a decision, areas to pay attention to in your desktop and rack guitar effects are connectivity, portability and, of course, the actual effects that come loaded on the unit. Choosing the right model for you is a matter of finding the one that offers the connections you need and the effects you want, all in a package that's portable, semi-portable or rack-mounted depending on how you'll be using it.