A Multi-Mode Filter typically (but not always) offers four different types of filters:
- Lowpass Filter
- Designed to remove frequencies above the specified cutoff frequency.
- Highpass Filter
- Designed to let high frequencies pass and attenuate low frequencies.
- Bandpass Filter
- Designed to allow a specified range of frequencies through while attenuating the remaining spectrum.
- Band Reject Filter (Notch Filter)
- Designed to stop a specified band of frequencies from passing. The opposite of a bandpass filter.
Some Multi-Mode filters offer simultaneous outputs or a switch to select the mode of the single output.
Multi-Mode filters come in a variety of forms and are useful for isolating specific frequencies.
Check out this webpage that has some information on CEM and other analog integrated circuits (chips) that were commonly found in Analog Synthesizers.