Continuous filters using digital techniques and incorporating variable frequency delay lines†
A.G.J. Holt, C. PULÉ · International Journal of Electronics · 1970
The term digital filter usually describes a processing unit which operates on an input signal at discrete intervals of time. The output characteristic of such a process is to filter out certain frequencies existing in the input waveform. It is shown that these filters can be used in a conventionally continuous manner by using a continuous delay line, and by changing the constant delay line to a variable delay line it is possible to obtain other related transfer functions. Use of digital filters in a multi-path configuration to extend their frequency range is also mentioned.