Filter  - This is a circuit that passes only a limited range of frequencies. There are four basic types of filters:

1. Low Pass - this filter passes all frequencies below a specific frequency (known as the cutoff frequency)
2. High Pass - this filter passes all frequencies above a specific frequency (known as the cutoff frequency)
3. Band Pass - this filter passes a only limited range of frequencies on either side of its center frequency
4. Band Pass - this filter passes all frequencies outside a limited range of frequencies on either side of its stop frequency