Ruth Melody Misbow Siallagan, Mauly Purba, Vanesia Amelia Sebayang, and Junita Batubara, “THE SINGING CHURCH: AN ANALYSIS OF VOCAL DEVIATIONS IN CONGREGATIONAL SINGING - A STUDY OF HKBP CONGREGATIONAL SINGING TECHNIQUES”, MORFAI, vol. 6, no. 2, pp. 1371–1378, Dec. 2025.