What Does The High Pass Filter Do

An sound loftier laissez passer filter (HPF) is an equalization tool that attenuates all frequencies below a set up point. In other words, loftier pass filters remove low frequencies while allowing high frequencies to pass through. They are used in almost every application of audio applied science.

Understanding how and when to utilize a high pass filter is a unproblematic skill that will drastically meliorate the quality of your mixes. Whether you lot are mixing studio recordings, live sound performances, or tuning consumer audio systems, information technology is essential to larn to harness the power of this uncomplicated tool. In this post, you'll learn what loftier laissez passer filters are, how they work, and when to use them.

An audio high pass filter (HPF) is an equalization tool that attenuates, or reduces, all frequencies below a set betoken.

What is a High Laissez passer Filter?

At that place are ii principal types of sound pass filters: high pass and low laissez passer. These terms are oftentimes dislocated. High laissez passer filters allow high frequencies to laissez passer through the filter, low pass filters allow low frequencies to pass through the filter.

The post-obit image shows a frequency response graph of pink noise. Every octave is evenly represented, forming a straight line from 20Hz to 20kHz:

The next prototype shows the aforementioned pink dissonance after beingness candy through a high laissez passer filter gear up to 500Hz. The frequencies in a higher place 500Hz are unaltered, but the frequencies below 500Hz have been adulterate:

Pink Noise Frequency Response - High Pass Filter

Heed to the following audio example of music processed through a high pass filter:

Loftier pass filters are congenital-in to some microphones and are near always constitute on mixing consoles and digital audio workstations (DAWs). They are also incorporated into digital signal processors (DSPs) used for conferencing and telephony. In almost all cases, high laissez passer filters are placed toward the beginning of the signal chain.

How to Use a High Pass Filter

This section will explore the basic performance of a high pass filter.

High Pass Filter Settings

Cutoff Frequency

The cutoff frequency setting of a high pass filter adjusts where in the frequency spectrum the filter begins. In the above case, 500Hz is the cutoff frequency.

Often the cutoff frequency is the point at which the filter attenuates past -3dB. Thus, the filter might actually begin at a higher frequency than stated by the cutoff adjustment.

The cutoff frequency settings of most high pass filters are infinitely variable, meaning that an engineer can set the cutoff frequency more precisely, using a knob. A high pass filter that does not have an infinitely variable cutoff frequency setting merely allows for specific frequencies to be selected, using a switch.

Gradient (Q)

The slope of a loftier pass filter determines the rate of attenuation. It is measured in decibels (dB) per octave.

The slope of a high laissez passer filter is sometimes adjusted using the Q setting. Mutual high pass filter slopes are 6dB, 12dB, 18dB, and 24dB per octave.

Imagine a high pass filter with the cutoff frequency set to 400Hz and a slope of 12dB per octave. The following chart shows the attenuation of each frequency relative to the cutoff frequency:

Frequency	Attenuation
400 Hz (cutoff frequency)	0 dB
200 Hz (one octave beneath 400 Hz)	-12 dB
100 Hz (2 octaves below 400 Hz)	-24 dB
50 Hz (iii octaves below 400 Hz)	-36 dB

Adjusting the slope of a high laissez passer filter allows an engineer to choose between drastic attenuation over a pocket-sized range of frequencies (steep) or gradual attenuation over a larger range of frequencies (gentle).

When to Use a High Pass Filter

In professional audio, loftier pass filters are used very oftentimes. This section will explore the various reasons to utilize a high pass filter.

1.) Remove Extraneous Low Frequencies

Each instrument produces sounds within a specific frequency band. High laissez passer filters are about commonly used to remove depression-frequency content that is not within an musical instrument's frequency range.

Equally a general starting point, y'all should place a high pass filter on each channel and adjust information technology according to the lowest frequency the sound source can produce. For instance, a male vocal volition not incorporate frequencies lower than about 80 Hz. With this in mind, you can remove all frequencies lower than 80Hz using a high pass filter. This can exist adapted after, just setting this upwardly from the kickoff quickly fixes a lot of problems and creates a good starting bespeak.

2.) Remove Environmental Racket

Traffic, current of air, and HVAC systems can create racket in your audio point. Luckily, these noises are primarily composed of low-frequency energy. Using a high laissez passer filter will allow you lot to remove the rumbling effects of these noises without affecting the signal y'all wish to record.

Information technology'due south e'er best to eliminate the source of the racket itself rather than try to remove it afterward. Turn off whatsoever fans, refrigerators, or HVAC systems for each session if possible. Oftentimes these sounds are not able to exist eliminated, such as in live sound or conferencing applications. In these cases, high pass filters are the best selection for reducing their effects. Listen closely to both the sound source and noise sources during audio check.

three.) Remove Plosives

Plosives, or P-pops, are vibrations of a microphone diaphragm acquired past gusts of air created past a vocalist. Although it is all-time to prevent plosives by using good microphone technique and a pop filter, they can sometimes be removed through the use of a high pass filter.

Plosives are comprised of depression frequencies. Equally you motility the high laissez passer filter higher, you will notice the popping sounds will brainstorm to sound thinner. You lot may reach a point when the plosive sound and the vocalizer occupy the aforementioned frequency band. This means that to remove the plosive completely would require removing some of the vocal signal, too. This is why it is all-time to prevent plosives before pressing record.

Learn more about pop filters in this Audio Academy article.

iv.) Remove Handling Noise

In live sound or conferencing situations, microphones may be adjusted by the user while in utilise. This causes a low-frequency rumble that can be reduced by applying a high pass filter.

Treatment noise includes footsteps on a stage, vibrations on a conference tabular array, and dropped microphones. Setting a high laissez passer filter volition help to ensure that treatment noises are reduced.

five.) Isolate Sound Sources

Often sound from one source will leak into other microphones in the room. High pass filters can assistance to improve isolation between instruments.

If you place your microphones so that their polar patterns pass up the high-frequency sounds coming from other sources in the room, only low-frequency leakage will be captured. This low-frequency content tin be removed with a high pass filter.

6.) Shape Tone for Mix Clarity

Even if a audio source is capable of producing low-frequency energy, you may still wish to attenuate it to forbid masking other instruments. High laissez passer filters tin exist used to carve infinite for the other components of a mix.

Kick drums create sub-bass frequencies that might non be benign to the mix. Acoustic guitar bodies might vibrate or resonate at frequencies lower than the notes being played. A bass guitar and a kick pulsate might compete for the aforementioned frequency ring. High pass filters can exist used to alter the tone of sounds so that they can fit together more than cohesively.

7.) Increase Proceeds Before Feedback

Low frequencies are less directional than high frequencies. This means that the beginning frequencies to feedback in audio reinforcement situations are often low frequencies. For this reason, it is important to use a loftier laissez passer filter to reduce the possibility of a low-frequency feedback loop.

Start by removing unnecessary low frequencies from each aqueduct. If depression-frequency feedback is yet occurring, attempt rolling the high pass filter a bit higher to eliminate the possibility of feedback.

To learn more about preventing feedback, bank check out this Sound University commodity.

8.) Optimize Headroom

Yous might notice that low frequencies take up a disproportionate amount of headroom. Often this causes meters to be misleading. Removing unnecessary low-frequency energy helps to ensure that you lot are optimizing the available headroom for the about important frequency bands.

Using a high pass filter tin can prevent a compressor from engaging prematurely based on low-frequency free energy. Without a high pass filter, too much low-frequency content tin can cause an amplifier to work unnecessarily hard to produce frequencies that will not fifty-fifty be heard through the speakers.

9.) Fix Speaker Crossover

Speaker systems are often comprised of several drivers. Common configurations include subwoofers, woofers, and tweeters. Loftier and low pass filters can be used to ship only specific frequency bands to each driver.

If low-frequency energy is sent to a high-frequency tweeter, it can harm the diaphragm and vocalization coil. Use the speaker's manufacturer specifications for setting a crossover point.

Read this Sound Academy article to acquire everything you demand to know about speaker crossovers.

Retrieve Outside the Box

At present you know the most common and conventional ways to utilise high laissez passer filters. This knowledge will help you navigate the common situations, merely also the more unique challenges of audio. Apply your imagination and what you know about these tools to creatively solve issues that might come up in the field.