OBTAIN: Real-Time Beat Tracking in Audio Signals

Abstract—In this paper, we design a system in order to perform the real-time beat tracking for an audio signal. We use Onset Strength Signal (OSS) to detect the onsets and estimate the tempos. Then, we form Cumulative Beat Strength Signal (CBSS) by taking advantage of OSS and estimated tempos. Next, we perform peak detection by extracting the periodic sequence of beats among all CBSS peaks. In simulations, we can see that our proposed algorithm, Online Beat TrAckINg (OBTAIN), outperforms state-of-art results in terms of prediction accuracy while maintaining comparable and practical computational complexity. The real-time performance is tractable visually as illustrated in the simulations. 1

Index Terms—Onset Strength Signal, Tempo estimation, Beat onset, Cumulative Beat Strength Signal, Peak detection I. INTRODUCTION The beat is a salient periodicity in a music signal. It provides a fundamental unit of time and foundation for the temporal structure of the music. The significance of beat tracking is that it underlies music information retrieval research and provides for beat synchronous analysis of music. It has applications in segmentation of audio, interactive musical accompaniment, cover-song detection, music similarity, chord estimation, and music transcription. It is a fundamental signal processing task of interest to any company providing information services related to music [1]. A. Related Works Many works have been carried out in offline beat tracking. One can find effective algorithms in the literature which perform beat tracking in an offline fashion [2]. It is however important to mention some of previous works on beat tracking. Aubio [3] is a real-time beat tracking algorithm which is available as a free application. Aubio has been used in entertainment applications like Sonic Runway [4] in 2016. IBT [5] is a state-of-the-art real-time algorithm in this field. IBT is based on BeatRoot [6] tracking strategy which is a state-of-the-art offline tracking algorithm. BeatRoot system takes advantage of two pre- processing and processing stages. In the pre-processing stage, a time-domain onset detection algorithm is used which calculates onset times from peaks in the slope of the amplitude envelope. The processing stage consists of two blocks. The first block uses a clustering algorithm on inter- onset intervals and generates a set of tempo hypotheses by

Manuscript received August 15, 2017; accepted September 6, 2017. Corresponding author: Ashkan Esmaeili examining the relationships between clusters. The second block is a tracking block. In this block, a multiple agent architecture is used, where each agent represents a hypothesis about the tempo. Performance of each agent due to the data is evaluated and the agent with the best performance returns output of the tracking system. Another state-of-the-art algorithm is Ellis [2]. Although Ellis method is not causal, some blocks of our system are based on this method. B. Our Contributions The goal of this paper is to provide a fast and competitive beat tracking algorithm for audio signals that can be easily implemented in real-time setting. As our key contributions, we

1. propose a simple yet fast beat tracking algorithm for
   audio signals, 2) extend the algorithm to real-time implementation,
2. compare the algorithm to previous results to show that it outperforms state-of-art algorithm prediction accuracy while maintaining comparable and practical computational complexity,
3. implemented our method on an embedded system (Raspberry Pi 3) to demonstrate its effectiveness and reliability in real-time beat tracking,
4. participated in a real-world challenge (IEEE SP Cup
5. and received honorable mention for our excellent beat tracking algorithm and annotation. II. OBTAIN ALGORITHM The proposed approach follows a relatively common architecture with the explicit design and tries to simplify each step and modify them. Therefore, they can be applied in the real-time setting. We call our algorithm OBTAIN (a pseudo-abbreviation of Online Beat TrAckINg). We will elaborate upon the blocks of this system throughout the paper and compare it to state-of- art methods. There are four main stages to the algorithm, as shown in Fig. 1. The initial audio input has a sampling rate of 44100 Hz. A. Generating Onset Strength Signal (OSS) Beat tracking is an audio signal processing tool which is based on onset detection. Onset detection is an important issue in signal processing. It can be widely

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