TSE3 (Trax Sequencer Engine v3) is a powerful open source sequencer engine written in C++. It is a sequencer engine because it provides the actual driving force elements of a sequencer but provides no form of user interface.
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Since the 0.0.7 version, the TSE3 library has been greatly improved. There is support for multiple threads and the Alsa library, whilst other improvements include a much tidier API, better documentation, and more robust callback framework. The library is now in use by a number of Linux multimedia projects.