A high-pass (low-cut) and/or low-pass (high-cut) filter may also be included on equalizers or audio consoles. High-pass and low-pass filters restrict a given channel's bandwidth extremes. Cutting very low frequency sound signals (termed infrasonic, or "subsonic") reduces the waste of amplifier power which does not produce audible sound and which moreover can be hard on the low-range speakers. A low-pass filter to cut ultrasonic energy is useful to prevent interference from radio frequencies, lighting control, or digital circuitry creeping into the power amplifiers. Such filters are often paired with graphic and parametric equalizers to give the audio engineer full control of the frequency range. High-pass filters and low-pass filters used together function as a band-pass filter, eliminating undesirable frequencies both above and below the auditory spectrum. A band-stop filter, does the opposite. It allows all frequencies to pass except for one band in the middle. A feedback suppressor, using an microprocessor, automatically detects the onset of feedback and applies a narrow band-stop filter (a notch filter) at specific frequency or frequencies pertaining to the feedback.