An equalizer equipped with an audio high pass filter (HPF) dampens all frequencies below a specified threshold. High pass filters, in other terms, eliminate low frequencies while enabling higher frequencies to get through. They’re employed in practically every audio technological innovation.
Knowing when and how to apply a high pass filter is a basic technique that will significantly enhance your production performance. It’s critical to master the capability of this basic tool, whether you’re tuning consumer sound systems, mixing studio records, or performing live sound. You’ll learn what exactly high pass filters are, how they operate, and when to use them in this article.
What Is A High Pass Filter?
Low pass and high pass audio filters are the two most used types. These words are frequently misunderstood. Low pass filters enable low frequencies to get through, whereas high pass filters enable high frequencies.
Some microphones have built-in high pass filters, and mixing consoles and digital audio workstations (DAWs) nearly always have them. They’re also found in digital signal processors (DSPs) used in telephony and conferencing. High pass filters are usually always used at the start of the signal chain.
Types of High Pass Crossovers
High pass filters are divided into three categories. Each one has its own set of advantages, disadvantages, and uses.
Speaker Crossovers (Passive filters)
Instead of employing electronics that require power, a speaker crossover, also known as a passive filter, uses passive electrical components. Capacitors, resistors, and inductors are examples of passive components.
A high pass speaker crossover is used on tweeter speakers to prevent bass and midrange frequencies from accessing them. The most basic form is a single electrolytic capacitor installed on the speaker.
Others employ an inductor and capacitor to provide a sharper cutoff to prevent undesirable sounds from entering the speaker. Because the structure is defined by predetermined component values, few, if any, of the options are adjustable.
Electronic Crossovers (Active filters)
An active filter, sometimes known as an electronic high pass filter, is a crossover that typically uses electronic elements and needs power. They’re frequently more flexible than passive filters and may include features such as:
- Selectable crossover slope
- Variable high pass cutoff frequency
- Controlling the phases
- Gain control (output and/or input levels that can be adjusted)
Most electronic high pass filters are built on operational amplifiers (op-amps), tiny transistor amplifiers built into an integrated circuit (IC). They are quite efficient regarding energy consumption, feature set, and size.
Home stereos, preamp units, vehicle amplifiers, stereo mixing boards, and other sounds electronic equipment use active filter designs.
Digital (software based) crossovers
A digital high pass filter operates on sound signals that have been transformed into digital numbers using mathematical software operations before being transformed back to analog signals.
Several systems include a digital crossover:
- Chips that do digital signal processing (DSP) or sound products
- Audio applications for computers (editing, mixing, and more)
- Smartphone sound apps
A high pass filter sound crossover is accomplished utilizing mathematical algorithms (z transforms) programmed in software procedures in every situation. When a song input is generated, the code decodes the digital form (binary numerical value), leading to an output result that is significantly below the crossover frequency.
In-home stereo receivers, automotive audio head units, and audio processing and recording software, digital crossovers are used in conjunction with a parametric or graphic EQ.
How to Use a High Pass Filter
This chapter will go through the basics of how a high pass filter works.
High Pass Filter Configuration
The cutoff frequency of a high pass filter determines where the filter starts in the frequency range.
This type of frequency setting is frequently the -3dB attenuation level of the filter. As a result, the filter may begin at a higher rate than indicated by the cutoff setting.
The cutoff frequency of some of the typical high pass filters can be changed indefinitely, allowing an engineer to fine-tune the cutoff frequency using a knob. Without an infinitely changeable cutoff frequency configuration, a high pass filter only permits the selection of certain frequencies via a switch.
A high pass filter’s slope determines how much attenuation occurs. It is expressed in decibels per octave (dB).
A high pass filter’s slope can be changed using the Q option. 6dB, 12dB, 18dB, and 24dB per octave are popular high pass filter slopes.
By altering the gradient of a high pass filter, an engineer can choose between intense attenuation over a narrow frequency range (steep) or progressive attenuation over a larger range of frequencies (gentle).
When To Use A High Pass Filter
This chapter will go over the various reasons for utilizing a high pass filter.
Remove Any Low-Frequency Interference
Each instrument generates sound in a particular frequency range. An instrument’s frequency range can be narrowed by using a high pass filter to remove low-frequency noise.
As a general guideline, each channel should have a high pass filter set to the lowest frequency the audio source can deliver. A male vocal, for instance, will not have frequencies below 80 Hz. A high pass filter could be used to eliminate any frequencies below 80Hz. This can be modified later, but doing it correctly the first time eliminates a lot of problems and gives you a great start.
Get Rid of Environmental Noise
Your audio signal may be affected by wind, traffic, and HVAC systems. Fortunately, the majority of these noises are composed of low-frequency energy. With a high pass filter, you can minimize the rumbling effects of these disturbances without harming the signal you wish to capture.
It’s always better to get rid of the cause of the disturbance instead of trying to get rid of it later. If feasible, switch off any refrigerators, fans, or HVAC systems for each session. In some cases, like in conferencing applications and live sound, these sounds cannot be avoided. High pass filters are the greatest choice for limiting their impact in these situations. During soundcheck, pay special attention to both the audio and noise sources.
Plosives, often known as P-pops, are microphone diaphragm vibrations induced by a vocalist’s air gusts. Although this is better to avoid plosives by employing a pop filter and good microphone techniques, a high pass filter can occasionally be used to remove them.
Plosives are made up of low-frequency components. You will note that the popping sounds become thinner as you raise the high pass filter. The plosive sound and the singer could potentially share the same frequency band. Several vocal signals would have to be deleted in order to eliminate the plosive. That’s why plosives should be avoided before clicking record.
Eliminate Handling Noise
Microphones can be modified while in use in conferencing or live sound scenarios. A high pass filter can be used to decrease the low-frequency echo caused by this.
Vibrations on a conference table, footfall on a stage, and fallen microphones are all examples of noise management. Applying a high pass filter can aid in the reduction of handling noises.
Separate The Sound Sources
Numerous microphones in the area frequently pick up sounds from a single source. High pass filters can assist in increasing instrument isolation.
If you place your microphones in such a way that their polar arrangements exclude high-frequency noises from other sources in the area, only low-frequency leaks will be detected. A high pass filter can be used to remove the low-frequency material.
Tone Shaping for Mix Clarity
Even though an audio source can generate low-frequency energy, it should be attenuated to avoid obscuring other instruments. High pass filters can be utilized to free up room in a mix for other elements.
Sub-bass frequencies are produced by kick drums, which may or may not be acceptable in a mix. Acoustic guitar bodies can resonate or vibrate at lower frequencies than the notes they’re playing. There may be frequency range competition between a kick drum and a bass guitar. High pass filters adjust the tone of sounds to make them blend better together.
Boost Gain Before Feedback
Low frequencies have fewer directional characteristics than high frequencies. This explains that low frequencies are frequently the first to receive feedback in audio augmentation scenarios. As a result, it is necessary to employ a high pass filter to avoid the possibility of a low-frequency feedback loop.
Start by removing any low frequencies from each channel that aren’t essential. If low-frequency feedback persists, try increasing the high pass filter’s gain to remove the potential of feedback.
As you may have seen, low frequencies consume a substantial quantity of headroom. This frequently leads to meters that are inaccurate. Removing unnecessary low-frequency power makes more headroom available for the most important frequency bands.
Low-frequency energy can cause a compressor to engage early if a high pass filter is used. In the absence of a high pass filter, too much low-frequency content might cause an amplifier to work too hard to generate frequencies that wouldn’t be audible through the speakers.
Configure Speaker Crossover
Several drivers are frequently used in speaker setups. Woofers, subwoofers, and tweeters are common setups. Only certain frequency bands can be sent to each driver using high and low pass filters.
The voice coil and diaphragm can be damaged when low-frequency power is supplied to a high-frequency tweeter. Set the crossover point according to the speaker’s company’s requirements.
Useful Applications for High Pass Filters
Using a Microphone and Recording studio
High pass filters are important in the studio for a variety of reasons:
- Avoiding touching or rumbling sounds from being recorded as a result of gear being handled and changed
- Eliminating plosives (pops) from the breath of a singer
- Changing the tone of sound frequencies during mixing
- During recording, separating sound sources from separate instruments
Benefits of A High Pass Filter in Automobile Audio
High pass filtering is commonly found in passive speaker crossovers, automotive amplifiers, installation add-on accessories, built-in car stereos, equalizers (EQs), or signal processors in automobile sound systems.
They can assist offer enhanced sound in a variety of ways:
- Producing clearer audio with more power via compact speakers and tweeters
- Keeping tweeters safe from damage or distortion caused by bass
- To hide low-frequency bass from the primary speakers, allowing subwoofers to manage it for enhanced sound quality.
Digital high pass filters with variable slopes are now incorporated into some head units. Many vehicle amplifiers have a high-pass or low-pass crossover functionality, and some even have a variable cutoff frequency. Others have a predetermined cutoff point that cannot be altered.
Home Stereo High Pass Filters
High pass filters are commonly found in home stereos for a number of reasons:
- Some audio systems have low-quality speakers, which distort and sound bad when the bass is turned up. In certain circumstances, using a high pass filter can assist to prevent this.
- Filtering bass to the main speakers when a home theater system or stereo receiver includes a subwoofer feed might assist prevent too much bass being generated.
- For clean singing in movies, the amount of sound supplied to the center channel speaker is limited.
- Surround sound audio channel processing is built into the home theater.
Home stereo high pass filters, like automobile stereo high pass filters, aren’t always switched on by default; in many instances, you’ll need to examine menu options and activate them.
Explanation of Subsonic Filters
A subsonic filter is a high pass filter with a very low crossover frequency, typically about 30 or 20Hz, designed to block low-frequency signals that we cannot hear from being routed to a subwoofer; hence preventing power waste.
A subsonic filter is discretionary and not always required, but it may be advantageous under some circumstances. They’re more frequent in older sound and record players, but they can also be found in automobile audio equalizers and subwoofer bass.
For most individuals, the human hearing frequency range is somewhere about 30Hz. Sound waves at 20 Hz can be felt but not heard; therefore, using a lot of amplifier energy for something you can’t hear is wasteful. Rumble can be found in record players, and a subsonic filter can stop this from being exacerbated.
The most pleasing bass is around 40 to 50 Hz for “thump” in most songs. It’s about the same as rumbling or action sound in movies; thus no need for 20 to 30Hz.
You now know how to utilize high pass filters in the most systematic and traditional ways. This information will assist you in navigating regular scenarios as well as the more unusual obstacles that audio presents. Use your creativity and knowledge of these instruments to solve problems that may arise in the environment.
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