jMusic provides a library of classes for generating and manipulating music, and is a solid framework for computer assisted composition in Java. jMusic supports composers by providing a music data structure based upon note/sound events, and methods for working with that musical data. jMusic can read and write MIDI files, audio files, and its own .jm files. jMusic is designed to be extendible, encouraging you to build upon the functionality of jMusic by programming in Java to create your own music composition tools.
Sfront compiles MPEG 4 Structured Audio (MP4-SA) programs into efficient C programs that generate audio when executed. MP4-SA is a standard for normative algorithmic sound, which combines an audio signal processing language (SAOL) with score languages (MIDI and SASL). Under Mac OS X and Linux, sfront supports real-time, low-latency audio input/output and MIDI input. Under Mac OS X, sfront supports the creation of AudioUnit plug-ins. The documentation includes a book about SAOL programming.
Smurf is a GTK-based SoundFont editor. SoundFont files are a collection of audio samples and other data that describe instruments for the purpose of composing music. SoundFont files do not describe the music itself, but rather the sounds of the instruments. These instruments can be composed of any digitally recordable or generated sound. This format provides a portable and flexible sound synthesis environment that can be supported in hardware or software. Note that Swami is the successor to Smurf and is an entire object-oriented rewrite of it.
SoundTracker is a pattern-oriented music editor (similar to the DOS program 'FastTracker'). Samples are lined up on tracks and patterns which are then arranged to a song. Supported module formats are XM and MOD; the player code is the one from OpenCP. A basic sample recorder and editor is also included.
Spiral Synth is a physically modelled polyphonic analogue synthesizer. It is capable of creating the kind of sounds made by hardware analogue synths, the noises used in electronic music. You can also use it to make stranger sounds too. MIDI is supported, and it uses the standard OSS/Free sound output (/dev/dsp).
STK is a set of audio signal processing C++ classes and instruments for music synthesis. You can use these classes to create programs which make cool sounds using a variety of synthesis techniques. This is not a terribly novel concept, except that STK is very portable and completely user-extensible.
TerminatorX is a realtime audio synthesizer that allows you to "scratch" on digitally sampled audio data (*.wav, *.au, *.mp3, etc.) the way hiphop-DJs scratch on vinyl records. It features multiple turntables, realtime effects (built-in as well as LADSPA plugin effects), a sequencer, and an easy-to-use GTK+ GUI.
The Two Dimensional Spatialization of Sound package takes a single monaural sound signal and processes it to create a binaural signal that places the source of the sound at a selectable arbitrary place around the listener. The package makes use of a set of HRTF Measurements of a KEMAR Dummy-Head Model created by Bill Gardner and Keith Martin of the MIT Media Lab. The sound spatialization software is ANSI C, and can be ported to any platform which will support the sound I/O requirements. The package also includes an FFT written in well-structured C.