Four timely insights on automatic chord estimation

Automatic chord estimation (ACE) is a hallmark research topic in content-based music informatics, but like many other tasks, system performance appears to be converging to yet another glass ceiling. Looking toward trends in other machine perception domains, one might conclude that complex, data-driven methods have the potential to significantly advance the state of the art. Two recent efforts did exactly this for large-vocabulary ACE, but despite arguably achieving some of the highest results to date, both approaches plateau well short of having solved the problem. Therefore, this work explores the behavior of these two high performing, systems as a means of understanding obstacles and limitations in chord estimation, arriving at four critical observations: one, music recordings that invalidate tacit assumptions about harmony and tonality result in erroneous and even misleading performance; two, standard lexicons and comparison methods struggle to reflect the natural relationships between chords; three, conventional approaches conflate the competing goals of recognition and transcription to some undefined degree; and four, the perception of chords in real music can be highly subjective, making the very notion of “ground truth” annotations tenuous. Synthesizing these observations, this paper offers possible remedies going forward, and concludes with some perspectives on the future of both ACE research and the field at large.