Real-time beat tracking for drumless audio signals: Chord change detection for musical decisions

Abstract

This paper describes a real-time beat-tracking system that detects a hierarchical beat structure in musical audio signals without drum-sounds. Most previous systems have dealt with MIDI signals and had difficulty in applying, in real time, musical heuristics to audio signals containing sounds of various instruments and in tracking beats above the quarter-note level. Our system not only tracks beats at the quarter-note level but also detects beat structure at the half-note and measure levels. To make musical decisions about the audio signals, we propose a method of detecting chord changes that does not require chord names to be identified. The method enables the system to track beats at different rhythmic levels – for example, to find the beginnings of half notes and measures – and to select the best of various hypotheses about beat positions. Experimental results show that the proposed method was effective to detect the beat structure in real-world audio signals sampled from compact discs of popular music.