Polyphonic Audio Key Finding Using the Spiral Array CEG Algorithm

Key finding is an integral step in content-based music indexing and retrieval. In this paper, we present an O(n) real-time algorithm for determining key from polyphonic audio. We use the standard Fast Fourier Transform with a local maximum detection scheme to extract pitches and pitch strengths from polyphonic audio. Next, we use Chew´s Spiral Array Center of Effect Generator (CEG) algorithm to determine the key from pitch strength information. We test the proposed system using Mozart´s Symphonies. The test data is audio generated from MIDI source. The algorithm achieves a maximum correct key recognition rate of 96% within the first fifteen seconds, and exceeds 90% within the first three seconds. Starting from the extracted pitch strength information, we compare the CEG algorithm´s performance to the classic Krumhansl-Schmuckler (K-S) probe tone profile method and Temperley´s modified version of the K-S method. Correct key recognition rates for the K-S and modified K-S methods remain under 50% in the first three seconds, with maximum values of 80% and 87% respectively within the first fifteen seconds for the same test set. The CEG method consistently scores higher throughout the fifteen-second selections.