A computer program that emulates the performance of an analog or digital synthesizer, a sampler, or an acoustic instrument. Virtual synthesizers earn this name because they operate entirely within the host computer’s CPU and use the computer’s internal or external audio hardware to generate sounds in place of the dedicated, proprietary hardware of most of the keyboards and synthesizers. Virtual synthesizers 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. Most of these instruments respond to MIDI continuous controller messages in the same manner as hardware synthesizers.
A virtual synthesizer often can operate in two modes. First, it may function as a plug-in in compatible host program such as Pro Tools, Digital Performer, SONAR, or another DAW. To do so, the virtual synthesizer must be written to support the plug-in format used by the host program, such as VST, MAS, DirectX or Audio Units. In addition, many virtual synthesizers can function in standalone mode, which means they can be played and programmed without requiring a host program to be open.