RISCHEL, J. . Heterodyne Filter. Annual Report of the Institute of Phonetics University of Copenhagen, [S. l.], v. 1, p. 13–14, 1967. DOI: 10.7146/aripuc.v1i.129689. Disponível em: https://tidsskrift.dk/ARIPUC/article/view/129689. Acesso em: 2 may. 2024.