@article{friend1968resistance, title = {Resistance-Capacitance Active Filters for Audio-Frequency Applications}, author = {Friend, David}, journal = {J. Audio Eng. Soc}, volume = {16}, number = {1}, pages = {94, 96, 98, 100, 102, 104, 106, 108, 110}, year = {1968}, url = {https://www.aes.org/e-lib/browse.cfm?elib=1664} }