About Virtual Instruments:
Every musician wants to own a warehouse full of vintage instruments and effects, as well as all the new, state-of-the-art gear they can cram into their studio or workspace. Over the years there have been so many classics, from the throaty growl of tone-wheel organs to the sonorous tones of a full-sized grand piano to the rich, fat waveforms of classic analog synths, that we've told ourselves, "Someday—someday I'll have one of those." Unfortunately, time, space and money have frequently conspired against those desires. Fortunately, the development of virtual instruments provided a solution we can live with.
A virtual instrument is, simply put, a musical instrument that has been created in software. It may be a softwarerecreation of a classic instrument, like multiple samples of a 9' grand, meticulously miked and recorded, then played back within a plug-in's architecture or it could be a digitally modeled version of the internal circuitry of some long-gone analog synthesizer or classic beatbox. It can also be a totally new instrument, using algorithms that are a hybrid of different technologies that don't play together well in the physical world, but make beautiful music together in the virtual world.
You can start stocking your warehouse full of instruments with a general purpose package that offers a wide assortment of basic instruments. After a while, you'll probably want to expand with more specialized packages, like collections of world and ethnic instruments, or dedicated orchestral or horn packages that feature extremely detailed control over dynamics and playing parameters to create incredibly realistic (or surrealistic, if that's more your thing) results. A rapidly growing category is instrument collections tweaked for specific musical styles, like dubstep, trance, or electroswing. Whatever type of music you make, you can find just the right instrument and have it always available for tracking.