A computer program that emulates the performance of an analog or digital synthesizer, a sampler or an acoustic instrument. Virtual instruments earn this name because they operate entirely as software with no physical “box.” However, this is not actually correct, as virtual instruments simply utilize the host computer’s CPU and internal or external audio hardware to generate sounds in place of the dedicated, proprietary hardware of most of the keyboards and synthesizers we’ve been used to over the years. Virtual instruments can be of relatively simple design, such as a collection of samples with a playback engine, or they can use complex modeling algorithms to emulate analog synths of the past (called “virtual analog” synths). Most of these instruments will respond to MIDI continuous controller messages in the same manner as a hardware synthesizer.
Virtual instruments often can operate in two modes. First, they function as a plug-in in compatible host programs such as Pro Tools, Digital Performer, SONAR, or other audio/MIDI sequencers. To do so, the virtual instrument must be written to support the audio format used by the host program, such as VST, MAS, DirectX or Audio Units. In addition many virtual instruments can function in standalone mode, which means they can be played and programmed without requiring a host program to be open.