«ATIS Telecom Glossary». atis.org. Alliance for Telecommunications Industry Solutions. Consultado em 16 de janeiro de 2018
bldrdoc.gov
its.bldrdoc.gov
«Federal Standard 1037C». Institute for Telecommunication Sciences. Institute for Telecommunication Sciences, National Telecommunications and Information Administration (ITS-NTIA). Consultado em 16 de janeiro de 2018
Transactions of the American Society of Heating, Refrigerating and Air-Conditioning Engineers 1968 [2] Quote: 'A "purple noise," accordingly, is a noise the spectrum level of which rises with frequency.'