The SQLite website recommends using the “sl3” extension to signify that we're working with an SQLite version 3 database. If we examine the resulting file, ljdata.sl3 using the strings command, we see ...

New AUP3 Audacity project file format This new format is an SQLite 3 database that Audacity says should make editing audio a little faster. However, closing and saving a project will be a bit slower.