Virtual Studio Technology
Virtual Studio Technology (VST) is a type of interface for integrating software audio synthesizer and effect plugins with audio editors and hard-disk recording systems. VST and similar technologies use digital signal processing to simulate traditional recording studio hardware with software. Thousands of plugins exist, both commercial and freeware, and VST is supported by a large number of audio applications. The technology can be licensed from its creator, Steinberg.
VST plugins are generally run within a Digital Audio Workstation, providing the host application with additional functionality. Most VST plugins can be classified as either instruments (VSTi) or effects, although other categories exist. VST plugins generally provide a custom GUI, displaying controls similar to the physical switches and knobs on audio hardware. Some (often older) plugins rely on the host application for their UI.
VST instruments include software simulation emulations of well-known hardware synthesizer devices and samplers, emulating the look of the original equipment and its sonic characteristics. This enables VSTi users to use virtual versions of devices that may be otherwise difficult to obtain.
VST instruments require notes to be sent via MIDI in order to output audio, while effect plugins process audio data (some effect plugins do require a MIDI input too though, for example they might use MIDI sync to modulate the effect in sync with the tempo). MIDI messages can often also be used to control parameters of both instrument and effect plugins. Most host applications allow the audio output from one VST to be routed to the audio input of another VST (known as chaining). For example, output of a VST synthesizer can be sent to a VST reverb effect for further processing.
The VST interface specification and SDK was released in 1996, coinciding with the release of Steinberg Cubase 3.02. Included with Cubase were the first available VST format plugins. Espacial, Choirus, Stereo Echo and Auto-Panner.
The VST interface specification was updated to version 2.0 in 1999. One of the additions was the ability for plugins to receive MIDI data. This allowed for the introduction of VSTi (Virtual Studio Technology Instrument) format plugins. VST Instruments can act as standalone software synthesizers, samplers or drum machines.
The VST interface specification was updated to version 2.4 in 2006. Changes included the ability to process audio using 64 bit precision.
The VST interface specification was updated to version 3.0 in 2008. Changes included:
- Audio Inputs for VST Instruments
- Multiple MIDI inputs/outputs
- Optional SKI (Steinberg Kernel Interface) integration
The VST interface specification was updated to version 3.5 in February, 2011. Changes included, among others, Note Expression where "each individual note (event) in a polyphonic arrangement can contain extensive articulation information, which creates unparalleled flexibility and a much more natural feel of playing." 
VST plugins 
There are three types of VST plugin.
VST instruments generate audio. They are generally either virtual synthesizers or samplers. Some, such as Native Instruments' Pro-53, specifically recreate the look and sound of famous synthesizers from years past (in this case, the Prophet-5). Some of the better known VST instruments include Massive, FM8, Absynth, Sylenth, Reaktor, and Omnisphere.
VST effects, such as reverb and phaser effects, process audio input. Other monitoring effects provide visual feedback of the input signal without processing the audio. Most hosts allow multiple effects to be chained.
VST hosts 
A VST host is a software application or hardware device that allows VST plugins to be loaded and controlled. The host application is responsible for handling the routing of digital audio and MIDI to and from the VST plugins.
There are a wide range of VST hosts available, including:
- Ableton Live
- ACID Pro
- Adobe Audition
- Adobe Premiere Elements
- Adobe Premiere Pro
- Ardour (open source)
- Audacity (only the Beta version (now Audacity 2.x) displays full VST graphical interfaces) (open source, Windows and Mac platforms only)
- DarkWave Studio
- Digital Performer (version 8 or higher)
- Steinberg Cubase
- Steinberg Nuendo
- Steinberg Wavelab
- FL Studio
- Giada - Your Hardcore Loopmachine
- LMMS (open source)
- Logic Pro
- Max MSP
- MadTracker 2
- Acoustica Mixcraft
- ModPlug Tracker
- Pro Tools
- PreSonus Studio One
- SSL Soundscape
- Vienna Ensemble Pro
- WavePad Sound Editor
- SADiE 6
- Turbo Play
- PowerDirector WaveEditor
- Mitov Software's AudioLab
- Sony Vegas
There are also stand-alone "dedicated hosts" whose sole purpose is to serve as a host for the VST plugins rather than as an extension of their sequencing or audio capabilities. These are usually optimized for live performance use, with features like fast song configuration switching. Examples of popular dedicated VST host software include:
- Brainspawn Forte
- eLektra Performance System (for 4 or 5 string electric violin only)
- Tobybear MiniHost
- Vienna Ensemble Pro
- Turbo Play
VST plugins can be hosted in incompatible environments using a translation layer, or shim. For example, FL Studio fundamentally supports only its own internal plugin architecture, but a native "wrapper" plugin exists that can, in turn, load VST plugins, among others. As another example, FXpansion offers a VST to RTAS (Real Time AudioSuite) wrapper (allowing VST plugins to be hosted in the popular Pro Tools digital audio workstation), and a VST to Audio Units wrapper (allowing VST plugins to be hosted in Apple Logic Pro Digital Audio Workstation).
Hardware VST hosts can load special versions of VST plugins. These units are portable and usable without a computer, although some of them require a computer for editing. Other hardware options include PCI/PCIe cards designed for audio processing, which take over audio processing from the computer's CPU and free up RAM. Examples of hardware VST hosts are:
- AudioStation (Seelake)
- RECEPTOR (Muse)
- V-Machine (SMProAudio)
- WERSI Expander
- EX-1,OPEN LABS
- Chameleon Synth Net
- Origin (Arturia)
- LIONTRACS Arranger
Some above can host VSTs and VSTis, and either run windows music applications like Cubase, Live, Pro Tools, Logic etc. or have their own DAW inside. Other are VST Hosts only and you shall have a separate DAW application to run together with them. Origin from Arturia is a hardware DSP system that houses several VST software synthesizers in one machine like Jupiter 50/80 from Roland.
Audio data can also be sent over a network using appropriate software, allowing the main host to run on one computer and VST plugins to run on peripheral computers.
Main VST host specification 
The mensurable Key Performance Indicators (KPI) for hardware (or software) VST hosts benchmark for live application (stage use) are: low warm-up time; low time required to switch between instruments and banks/ patches/ presets; low audio latency (less than 5 ms); good sound quality (sample rate); low CPU usage; low background noise; high input level dynamic range; greater user memory capacity.
The subjective aspects to be considered are: run under Windows, Linux, Mac, Android or other operating systems; run ASIO drive; run a great number of both free and commercial VST plug-ins; compatible with any kind of synthesis algorithms as additive, subtractive, physical modelling, sampling, FM synthesis, mixed and so on; offer a friendly Man Machine Interface (MMI) including touch screen capabilities; back-light screen for overnight operation; stable program routines without crashes; instrument parameters easily user configurable; ability to simulate the sound of a real instrument, if offered; open-architecture design for hardware and software with SDK; and, automatic detection of peripheral as MIDI keyboards, controllers and third part components; Considering hardware solutions: rugged construction suitable for live performance, with high life cycles quality jacks, connectors, switches, rotary and slider potentiometer. Musicians shall provide a no-break (UPS) for the entire hardware system to avoid electric power faults and use good cable extensions and plugs.
VST plugin standard 
The VST plugin standard is the audio plugin standard created by Steinberg to allow any third party developers to create VST plugins for use within VST host applications. VST requires separate installations for Windows, Mac OS X and Linux. The majority of VST plugins are available for Windows due to both Apple's proprietary Audio Unit software for OS X and the lack of information and patent encumbrances[specify] that make development difficult for Linux platforms.
Audio stream input/ output (ASIO) 
ASIO is a computer sound card driver protocol for digital audio specified by Steinberg, providing a low-latency and high fidelity interface between a software application and a computer's sound card. Whereas Microsoft’s DirectSound is commonly used as an intermediary signal path for non-professional users, ASIO allows musicians and sound engineers to access external hardware directly.
ASIO4ALL is a freeware hardware independent low latency ASIO driver for WDM audio devices. It uses WDM Kernel-Streaming and sometimes even more sophisticated methods to achieve its objectives.
VST plugins often have many controls, and therefore need a method of managing presets (sets of control settings).
Steinberg Cubase VST introduced two file formats for storing presets: an FXP file stores a single preset, while an FXB file stores a whole bank of presets. These formats have since been adopted by many other VST hosts, although Cubase itself switched to a new system of preset management with Cubase 4.0.
Many VST plugins have their own method of loading and saving presets, which do not necessarily use the standard FXP/FXB formats.
Competing technologies 
- Apple's Audio Units
- Digidesign's Real Time AudioSuite
- Digidesign's TDM
- LADSPA, DSSI and LV2 for Linux
- Microsoft's DirectX plugin
- Mark of the Unicorn's Motu Audio System
- JACK Audio Connection Kit (open source)
- JOST a free native implementation VST Host for Linux
- Propellerhead's Rack Extensions
Programming languages 
Steinberg's VST SDK is a set of C++ classes based around an underlying C API. The SDK can be downloaded from their website.
There are several ports available, such as a Delphi version by Frederic Vanmol, a Java version from the jVSTwRapper project at Sourceforge, and two .NET versions — Noise and VST.NET; this open source project also includes a framework which makes creating VST plugins easier and result in more structured code. VST.NET also provides support for writing managed host applications with a managed class that allows loading an unmanaged Plugin. A notable language supporting VST is Faust considering that it is especially made for making signal processing plugins, often producing code faster than hand-written C++.
In addition, Steinberg have developed the VST GUI, which is another set of C++ classes, which can be used to build a graphical interface. There are classes for buttons, sliders and displays etc. Note that these are low level C++ classes and the look and feel still have to be created by the plugin manufacturer.
A large number of commercial and open-source VSTs are written using the Juce C++ framework instead of direct calls to the VST SDK, because this allows multi-format (VST, AudioUnit and Real Time AudioSuite) binaries to be built from a single codebase.
See also 
- Software synthesizer
- Digital audio workstation
- LADSPA and LV2, similar open source standards.
- Audio Units, a similar standard by Apple Inc..
- SynthEdit, a VST/VSTi editor.
- Software effect processor
- Steinberg Cubase 3 (article), Sound on sound, 1996 jul.
- Cubase 3.7 (article), Sound on sound, 1999 sep
- KVR audio.
- News, KVR audio.
- VST 3.5 a milestone in VST development (News), Steinberg, 2011-02-10.
- VST plug-ins
- VST, Axi world.
- jVSTwRapper, Source forge.
- Noise, Google code.
- VST.Net, Codeplex.