Table 6.

Datasets and methods for data collection using acoustic signal.

Authors	Dataset	Method for Data Collection
Rocha et al. [59]	The final dataset contains 55 audio files	Microphone
Ericeira et al. [50]	Ten time-series in non-defective idlers and ten recordings for the defective ones. Each recording lasted for approximately 20 s	ultrasonic sensor
Liu et al. [8]	42 sets of acoustic data acquired from experiments, which is equal to 420 s of sound data acquisition.	microphone
Yang et al. [40]	Not reported	Sensor
Peng et al. [24]	A total of 8000 sets of sample data are collected	Sensor
Xiao-ping Jiang and Guan qiang Cao [41]	Not reported	Generated sound signal