A software instrument can be a synthesized version of a real instrument (like the sounds of a violin or drums), or a unique instrument, generated by computer software. Software instruments have been made popular by the convergence of synthesizers and computers, as well as sequencing software like GarageBand, Logic Pro (geared toward professionals), the open source project Audacity, and Ableton Live which is geared towards live performances. Also of note is software like Csound and Nyquist, which can be used to program software instruments. A software instrument is akin to a soundfont.
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Software instrument Wikipedia(Text) CC BY-SA