Ars Nova products all save in the SW4 (Songworks 4) format, which allows certain features unique to Ars Nova, but Songworks can import and export other formats as well. The importing of these especially can save you a lot of time, and exporting can be useful if you need to share music with different software.
ABC is a text-based format that is easily readable and can be altered using a text editor if you know how it works. This is especially popular for folk music files on the internet, such as fiddle tunes.
MIDI files are a very old format that contains no information regarding notation - they are primarily lists of note numbers and note times, though they do include information telling the meter and key. Many programs can import these and make a good guess about how they would best be notated. "Type 2" MIDI files do have separate note lists that can correspond to different staves, so that is the type we export. Another thing to keep in mind re MIDI is that it has no provision for distinguishing between sharps and flats - D# and Eb are the same number in MIDI. Songworks and Counterpointer will guess at what would be the best choice of sharp or flat whenever one is found that is outside the key signature.
This is by far the best universal format for music, though again there are certain features in SW4 files that have no counterpart in XML, such as the accompaniment patterns for chord symbols. We import files saved in the "Partwise" Music XML format and export the same way. Songworks does not currently export its chord symbols, but you can still save a lot of effort by importing a file instead of entering it by hand.
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