Thanks to the work of Jonathan Marmor, music21 now has a proof-of-concept linking with The Echo Nest, a great mostly-open framework for audio analysis with many python links. See the Transcribe Melodies link for more information. Full source code is available here. Thanks to Jonathan and to Echo Nest for making this linkage possible. While music21's primary focus will always be on symbolic data, we love audio analysis and hope we can add more features to make music information retrieval and analysis on audio files easier.