Reason is a popular music software program developed by Swedish software developers Propellerhead Software. It emulates a rack of hardware synthesizers, samplers, signal processors, sequencers and mixers. Reason can be used either as a complete virtual music studio, or as a collection of virtual instruments to be played live or used with other sequencing software.

Reason 1.0 was released in November 2000. The program's design mimics a studio rack into which users can insert virtual devices such as instruments, effects processors and mixers. These modules can be controlled from Reason's built-in MIDI sequencer or from other sequencing applications such as Pro Tools, Logic, Cubase and GarageBand via Propellerhead's ReWire protocol.

As of version 3.0, modules available include two mixers, a subtractive synthesizer, a graintable synthesizer and four different kinds of sample players - one with a step sequencer designed for drums/percussion, two for tonal instruments, and a sliced loop playback device. Effects include distortion, reverb, chorus, a vocoder and mastering effects. The Combinator device, introduced in version 3.0, allows users to combine multiple modules into one. Another device connects Reason to Propellerhead's (now discontinued) ReBirth.

One of the most striking aspects of Reason's interface comes into play with the Toggle Rack command, which flips the rack around to display the devices from the rear. Here the user can route virtual audio and control cables from one piece of equipment to another in an almost unlimited number of ways. This cable layout enables the creation of complex effects chains and allows devices to modulate one another in creative ways.

Unlike many other audio applications, Reason cannot record audio tracks or be expanded with third-party plug-ins. Some users complain about these limitations; others argue that they can be easily surmounted by using Reason in tandem with another application that has these capabilities.

A stripped-down version of Reason known as Reason Adapted is packaged as bonus software with other audio software such as Pro Tools LE. It restricts the user to a limited number of devices.

The program's name was taken from software used by the lead character in Douglas Adams's novel Dirk Gently's Holistic Detective Agency. Early in development it was known as Realizer (after the PPG Realizer). The English band The Prodigy has used Reason as a production tool, as have André 3000 of (Outkast) and Luke Vibert to lesser knowns like Mixer Jaëxx and others. Wonder Arillo, one of the songwriters on rapper T.I.'s hit "What You Know", used Reason on this song. In addition, numerous commercials and movies make extensive use of Reason. It is required, along with a laptop computer and other music production equipment, of new students in certain majors at the Berklee College of Music.

Source : http://en.wikipedia.org