1. Clinical Auscultation of the Heart;Levine,1949
2. Loudness, its definition, measurement and calculation;Fletcher;J. Acous. Soc. Am.,1933
3. Cardiac Auscultation;Butterworth,1960
4. Clinical Phonocardiography;Deuchar,1965
5. Clinical Auscultation of the Heart;Levine,1959