Ecasound is a software package designed for multitrack audio processing. It can be used for simple tasks like audio playback, recording, and format conversions, as well as for multitrack effect processing, mixing, recording and signal recycling. It supports a wide range of audio inputs, outputs, and effect algorithms. Effects and audio objects can be combined in various ways, and their parameters can be controlled by operator objects like oscillators and MIDI-CCs. A versatile console-mode user interface is included in the package.
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.
Swami is an instrument patch file editor using SoundFont files that allows you to create and distribute instruments from audio samples used for composing music. It uses FluidSynth, a software synthesizer, which has real time effect control, support for modulators, and routable audio via JACK. This project supersedes the Smurf SoundFont Editor, and is an entire object-oriented rewrite of it. The supporting libraries are GUI-independant and can be used in your own programs for doing SoundFont manipulation.
MidiKeys is a little application that displays a piano keyboard onscreen. You can click the keyboard or use the computer keyboard to play MIDI notes. The keyboard window can be made to float on top of other applications and supports transparency. Also, MidiKeys will optionally set up hotkeys for the computer keyboard so you can play notes in other applications (such as a sequencer) without having to switch back to MidiKeys. It works great on a PowerBook!
SynthTest is a somewhat simple application for OS X that allows you to pick a MIDI source, a MusicDevice AudioUnit, and an Effect or MusicEffect AudioUnit to play with. You can open an edit window for both the synth and effect. If they do not have a custom edit GUI, the generic editor view will be used. SynthTest has a reference implementation of preset support for Audio Units. It is primarily intended to be used by Audio Unit developers for testing purposes (the source is available), although it can be great fun to play with all by itself. It is complete enough to be used for live performances.
Hydrogen is a simple real-time Drum machine/sequencer. It features a graphical user interface based on Qt, a sample-based audio engine, Jack/ALSA/OSS/PortAudio and Export to disk audio drivers, ALSA MIDI input, ability to import/export XML-based song and drumkit files, 192 ticks per pattern, 16 voices with volume, mute, solo, ADSR, and pan capabilities, and import of samples in wave, au, and aiff format.