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A software synthesizer, also known as a softsynth, is a computer program or plug-in for digital audio generation. Computer software which can create sounds or music is not new, but advances in processing speed are allowing softsynths to accomplish the same tasks that previously required dedicated hardware. Softsynths are usually cheaper and more portable than dedicated hardware, and easier to interface with other music software such as music sequencers.
Hardware versus software 
Dedicated hardware synthesizers can have software as complex as a soft synth. The distinction is that softsynths run on a general purpose computer with a sound card, and the hardware (dedicated) synthesizers have the custom software built-in. The advantage to dedicated hardware is that it can be more stable, and also that it often has a user interface that is physical (knobs and sliders) and therefore easier to manipulate during performances. Many softsynths use mathematical algorithms which directly emulate the electronic components and circuitry of the original hardware synthesizer. This results in an exceptionally authentic sound, as well as allowing for some of the inconsistencies, such as oscillator drift caused by the thermal sensitivity of the components, to be added.
Types of softsynth 
There are a number of very popular hardware synthesizers which are no longer manufactured which have been emulated in software. The emulation can even extend to having graphics that model the exact placements of the original hardware controls. Some simulators can even import the original sound patches with accuracy that is nearly indistinguishable from the original synthesizer. Popular synthesizers such as the Minimoog and Yamaha DX-7, Korg M1, Prophet V, Oberheim OB-X, Roland Jupiter 8, ARP 2600 and dozens of other classics have been recreated in software.
Some softsynths are heavily sample based, and frequently have more capability than hardware units, since computers have fewer restrictions on memory than dedicated hardware synthesizers. Some of these sample based synthesizers come with sample libraries many gigabytes in size. Some are specifically designed to mimic real world instruments such as pianos. Many sample libraries are available in a common format like WAV or SoundFont, and can be used with almost any sampler based softsynth.
The major downside of using softsynths can often be more latency (delay between playing the note and hearing the corresponding sound). Decreasing latency requires increasing the demand on the computer's processor. When the soft synthesizer is running as a plug-in for a host sequencer, both the soft synth and the sequencer are competing for processor time. Multi-processor computers can handle this better than single-processor computers. As the processor becomes overloaded, sonic artifacts such as "clicks" and "pops" can be heard during performance or playback. When the processor becomes completely overloaded, the host sequencer or computer can lock up or crash. Increasing buffer size will help, but also increase latency. However modern professional audio interfaces can frequently operate with extremely low latency, so in recent years this has become much less of a problem than in the early days of computer music.
It is also possible to generate sound files "off-line", meaning the generation of sound information does not have to be in real time, or "live". For example, the input could be a MIDI file and the output could be a WAV file or an MP3 file. When one plays a WAV or MP3 file, they are only playing a pre-calculated wave-form(s) such that the computations are already done. The advantage of off-line synthesis is that the software can spend as much time as it needs to generate the resulting sounds, potentially increasing the quality of the results because the software can "take its sweet time". It could take 30 seconds of computing time to generate 1 second of sound (when played back in real-time) for example. The disadvantage is that any changes to the music specifications may not be immediately available for listening.
Plug-in compatibility 
Stand-alone softsynths run as a program on the computer so additional software is not required. Plug-in softsynths require a host application such as a Digital Audio Workstation, which records the music that is played. Common plug-in technologies include VST, Audio Units (AU), Avid Audio eXtension (AAX), Real Time AudioSuite (RTAS), DirectX instrument (DXi) and MOTU Audio System (MAS).
Typical software synthesizers 
Amongst the earliest successful software synthesizers were the S-YXG series from YAMAHA and the Virtual Sound Canvas by Roland under the name EDIROL.
S-YXG series 
Essentially, the software is a VxD (Win98) or WDM (WinXP) driver which emulates a synthesizer by utilizing the CPU to process MIDI data with a wavetable file loaded into memory as a sound library. S-YXG50 (WDM) is made up of two sound libraries (a 2 MiB [compressed] GM2 and a 4 MiB [compressed] XG sound set). Both versions can be downloaded from Microsoft’s Windows Update Catalog site free of charge.
Microsoft GS Wavetable SW Synth 
The Microsoft GS Wavetable SW Synth included in versions of Direct X as an integral part of DirectMusic is a version of the Roland Virtual Sound Canvas with GS sound set licensed by Microsoft from Roland Corporation in 1996. The wavetable file about 3 MiB in size is named "GM.DLS" which tells us that the wavetable is in DLS format.
QuickTime Music Synthesizer 
Newer Software Synthesizers 
Software Synth developers such as Arturia offer virtual editions of analog synths like the Minimoog, the ARP 2600, as well as the Yamaha GS20. Gforce produces a Minimoog with sounds designed by Rick Wakeman and version of the ARP Odyssey
Linux Synthesizer 
ZynAddSubFX is an open source software synthesizer for Linux, Mac OS X and even Windows. It can generate polyphonic, mutlitimbral, microtonal sounds in realtime. It is a free program, licensed under version 2 of the GNU General Public License.
Mobile Synthesizer 
Mobile Phones have become so high in processing power, that synthesizer applications (apps) can play with the same capabilities as the classic analog or digital synths. They can have several oscillators with pulse width modulated waveforms, frequency- and amplitude- modulation, ADSR envelope forming and a number of digital sound processing effects like filter, exciter, delay, chorus and reverb. One example is the Windows Phone Synthesizer.
Recently there have been many virtual synthesizers released for Apples iOS devices (iPad, iPhone, and iPod Touch). Many of these are from independent developers. Hardware manufacturers have also released apps for the iPad and iPhone including Moog Music, Korg, Akai, and Tascam. There is an online community that lists all iOS Apps for serious music production including DAW's, Synthesizers, Drum Machines, and Effects called iDesignSound.com.
Apple Logic Studio comes with a variety of Software Synths including FM, Bass, Analog, Ensemble as well as Electric Piano and Hammond B-3 emulation.
See also 
- Category:Software synthesizers
- Category:Music software plugin architectures
- Digital audio editor
- Modular synthesizer
- Music sequencer
- Digital audio workstation
- Sound module
- "Microsoft Licenses Sound Canvas Sounds From Industry Leader Roland Corp". Microsoft Corp. 1996-10-22. Retrieved 2009-07-23.
- "Roland Corp. Licenses Sound Canvas Sounds and C Format for Apple's QuickTime 3.0". Apple Inc. 1997-12-18. Retrieved 2009-07-23.
- "ZynAddSubFX project page at Sourceforge". Retrieved 31 July 2012.