High Pass Filter

A high pass filter (HPF) is a filter that tempers all the frequencies that are below the certain cutoff frequency and allows the frequencies that are above to pass. This filter can appear at many stages of the signal path. Such states are the microphone, the amplifier, the equalizer, or the plugin, for example. In this case, the slope of filter tempering tends to be quantified in decibels per octave. The slope is able to continue its path to extend into extremely low frequencies. This, in turn, lets the attenuation of the signal to an imperceptible amplitude.

High Pass Filter: Characteristics

High pass filters are common in studio recordings. They usually attenuate irrelevant low-frequency content, such as mechanical rumble and vocal plosives. By selecting a filter with a cutoff frequency that falls below the fundamental frequency range of the program, a high pass filter makes a difference between a low-frequency noise and a program signal.

HPFs: Their Applications 

The applications of a high pass filter are diverse. As part of an audio crossover, these filters direct high frequencies to a tweeter, while weakening bass signals that could damage the speaker or produce unwanted interference. For instance, experts know HPFs built into loudspeaker cabinets as passive filters, which can be of particular use. Extremely simple high pass filters for tweeters involve only a series of capacitors. Yet, the more sophisticated ones can include a low pass filter for the woofer—and even a capacitor and an inductor.

It’s fairly common for mixing consoles to have high pass filtering at each channel strip. Some models have fixed-slope, fixed-frequency HPF at 80 or 100Hz. Some other models have filters of a fixed slope and you can set within a certain range. Kick drum, bass guitar, and piano are sources that can work on low-frequency sounds.

High Pass Filter: an Example

Bruce Main is a veteran system engineer and live sound mixer. He recommends the use of high pass filters for most mixer input sources. This expert also says that DI unit inputs don’t need high pass filtering because they are not subject to modulation by low-frequency stage wash. Instead, they are low-frequency sounds coming from subwoofers and wrapping around the stage. According to Main, you can apply HPF to directional mics because they have a proximity effect.