A modular software music studio consists of a plugin architecture that allows the audio to be routed from one plugin to another in many ways, similar to how cables carry an audio signal

Audio signal processing

Audio signal processing, sometimes referred to as audio processing, is the intentional alteration of auditory signals, or sound. As audio signals may be electronically represented in either digital or analog format, signal processing may occur in either domain...

 between physical pieces of hardware.

All aspects of signal synthesis and manipulation are handled entirely by the plugin system. Signal synthesis is performed by "Generators" such as synthesizers, noise generator functions, sampler

Sample-based synthesis

Sample-based synthesis is a form of audio synthesis that can be contrasted to either subtractive synthesis or additive synthesis. The principal difference with sample-based synthesis is that the seed waveforms are sampled sounds or instruments instead of fundamental waveforms such as the saw waves...

s, and trackers. The signal can then be manipulated further by "Effects" such as distortions, filters, delays, and mastering plugins.

Free audio software

• SpiralSynthModular
• Pure Data
  Pure Data
  Pure Data is a visual programming language developed by Miller Puckette in the 1990s for creating interactive computer music and multimedia works. While Puckette is the main author of the program, Pd is an open source project with a large developer base working on new extensions to it. It is...
  
  
• jMax
• SynFactory
  SynFactory
  SynFactory is a free and open source software synthesizer for Windows. It is based on the same sound generating principles such as subtractive synthesis as used in vintage modular synthesizers. Patches can be built from separate components and connected together with virtual patch cables...
  
  
• aRts
  ARts
  aRts, which stands for analog Real time synthesizer, is an audio framework that is no longer under development. It is best known for previously being used in KDE to simulate an analog synthesizer....
  
  
• Jeskola Buzz
  Jeskola Buzz
  Jeskola Buzz is a freeware modular software music studio environment designed to run on Microsoft Windows via Microsoft .NET. It is centered around a modular plugin-based machine view and a multiple pattern sequencer tracker .Buzz consists of a plugin architecture that allows the audio to be routed...
  
  
• Psycle
  Psycle
  Psycle is a modular music production application to make music on Windows. Based on the tracker interface but featuring up-to-date features like VST compatibility and 96 kHz / 32bit wav rendering....
  
   is a tracker combined with modular capabilities
• Buzztard
  Buzztard
  Buzztard is a free software project to create a clone of the Buzz music composer. The driving motivation is to preserve the playability of the compositions made with Buzz. Songs are made by adding virtual sound generators and effects, connecting them, recording short musical phrases and arranging...
  
  
• Aldrin

Other audio software

• Reaktor
  Reaktor
  Reaktor is a graphical modular software music studio of proprietary license developed by Native Instruments. It lets musicians and sound specialists design and build their own instruments, samplers, effects and sound design tools. It is supplied with many ready-to-use instruments and effects, from...
  
  
• AudioMulch
  AudioMulch
  AudioMulch is modular audio software for making music and processing sound. The software can synthesize sound and process live and pre-recorded sound in real-time....
  
  
• Max/Msp
• Bidule
  Bidule
  Bidule is a commercial software application for the creation of interactive computer music and multimedia produced by the Canadian company Plogue Arts and Technology. It runs on both Windows and Mac computers....
  
  
• Reason
  Reason (program)
  Reason is a music software program developed by Swedish software developers Propellerhead Software. It emulates a rack of hardware synthesizers, samplers, signal processors, sequencers, and mixers, all of which can be freely interconnected in an arbitrary manner...
  
  
• SynthEdit
  SynthEdit
  SynthEdit is a shareware Windows application which uses a modular VPL to create music synthesizers and effects units. These can then be compiled as VST plug-ins for use in audio applications....
  
  
• SynthMaker
• SunVox
  SunVox
  SunVox is a compact cross-platform audio tracker with modular synthesizers.Features:* minimalistic scalable interface for working on any video resolution;...