1. School of Computer Science and Electronic Engineering, University of Essex, Colchester CO4 3SQ, UK
2. School of Sport, Rehabilitation, and Exercise Sciences, University of Essex, Colchester CO4 3WA, UK
3. The Key Laboratory of Intelligent Computing and Service Technology for Folk Song, Ministry of Culture and Tourism, Xi’an 710119, China
4. School of Computer Science, Shaanxi Normal University, Xi’an 710119, China