Interactive Music Theory Lab vs music21

Interactive Music Theory Lab is a free web app for learning and applying music theory. Chord Lab offers an interactive chord builder, chord library, piano keyboard, staff notation, voicings, and inversions. Scale Explorer covers more than 100 scales and maps their patterns on piano and fretboard. Theory Academy provides interactive lessons, guided tutorials, exercises, and subjects ranging from intervals to voice leading. Composition Studio lets users arrange progressions and song sections by drag and drop, receive theory-based suggestions, and export MIDI or PDF. The interface also lists MIDI and MusicXML import and export, along with PDF and audio export. Users can upload MP3, WAV, OGG, M4A, or FLAC files for chord-progression detection; clear recordings work better than complex mixes. The service requires no account and includes progress tracking. It offers guidance rather than writing songs for users, and the maker notes that bugs exist.

music21 is a free Python toolkit for computer-aided musicology, used to study music datasets, teach music theory, edit notation, analyze music, generate examples, and compose. It includes a corpus of thousands of encoded works, plus tools for searching that corpus, plotting pitch, and performing advanced analysis such as nPVI. The toolkit works with MIDI and MusicXML and can be extended to handle other formats. Its documentation recommends MuseScore for viewing and editing notation, and describes MusicXML readers including Finale, Sibelius, and Dorico. Optional integrations include LilyPond, Matplotlib, SciPy, PyAudio, and Pygame; music21 can also be used in web-based Jupyter Notebook. It runs on Linux, macOS, and Windows, with web use through Jupyter. The toolkit is BSD-licensed and costs nothing. Some corpus works have separate license restrictions. Users need some familiarity with Python, and music21 works primarily with symbolic music data rather than sound waves; it cannot read notation directly from images or PDFs.