What Is a Filter in Audio? (Explained)

Discover the basics of audio filters, their different types, applications, and popular tools in this beginner-friendly guide to enhancing your audio quality.

Are you tired of being “all filter and no substance”? Don’t worry! In this blog post, we’ll dive deep into the world of audio filters and reveal the secrets behind their mind-bending power. You’ll learn everything you need to know about what a filter in audio is, the various types available, and how they can transform your audio projects like a sonic superhero.

Imagine yourself in a room full of musicians, each playing their own instrument. It’s a beautiful symphony, but there’s one problem – the tuba player just can’t help but steal the show. That’s where audio filters come to the rescue! Just like a superhero swooping in to save the day, audio filters can help you isolate or enhance specific frequency ranges.

What is a filter in audio? A filter in audio is a tool used to selectively amplify or attenuate specific frequency ranges in a sound signal, allowing for noise reduction, equalization, and enhancing or isolating certain frequencies. These filters play a crucial role in improving audio quality and tailoring the sound to the desired outcome.

What is an audio filter?

Audio filters are electronic circuits designed to amplify or attenuate a specific frequency spectrum. This reduces unnecessary noise in the audio signal and improves the tone of the audio. Filters are essential in telecommunications and audio electronics.

Image of a woman in front of a microphone and monitor. Source: pexels
Image of a woman in front of a microphone and monitor. Source: pexels

Filters are a subset of amplifiers or passive circuits with frequency-dependent output. Filters can be classified in various ways, including construction, frequency response, or both. Audio filters are classified based on their construction as follows:

Passive filter

A passive filter comprises passive components such as a resistor and capacitor or a resistor and inductance. Because the impedance of capacitors and inductors varies with frequency, it is possible to build filters using resistor-capacitor, resistor-inductance, or resistor-capacitor-inductor combinations. These filters do not require any power source.

Active filter

Active filters are built with active components such as transistors or operational amplifiers. Using active components eliminates the necessity for inductance in the filter construction. This minimizes the size and cost of the circuit while increasing the filter’s efficiency. These filters are active filters because they require a DC biasing source for their active components.

My favorite MIDI keyboard (at the moment):

AKAI Professional MPK Mini MK3

What is a filter in audio? (explained) | 717qmgla7zl. Ac sl1500 | audio apartment
My favorite MIDI keyboard (at the moment):

AKAI Professional MPK Mini MK3

I’m loving the AKAI MPK Mini MK3 for its compact design and the range of controls. It’s one of my essential tools. The velocity-sensitive keys and MPC-style pads are great for making beats, while the thumbstick and knobs give me precise control.

Types of filters

There are various types of audio filters, each with its unique purpose and capabilities. Let’s explore the distinct characteristics of low-pass, high-pass, band-pass, and notch filters, giving you a solid understanding of how they work and how they can transform your audio projects.

1. Low-pass filters

These filters allow low frequencies to pass through while attenuating higher frequencies. They are commonly used in applications where it is necessary to eliminate high-frequency noise or to focus on the low-frequency components of a sound signal.

2. High-pass filters

High-pass filters work oppositely to low-pass filters, allowing high frequencies to pass through while attenuating low frequencies. They are often used to remove low-frequency noise, such as rumble or hum, or to emphasize high-frequency content in a sound signal.

3. Band-pass filters

A band-pass filter allows a specific range of frequencies to pass through while attenuating frequencies outside of this range. This type of filter is useful for isolating a particular frequency band, such as when focusing on a specific instrument within a mix or enhancing the clarity of a vocal recording.

4. Notch filters

Notch filters, also known as band-reject or band-stop filters, eliminate a narrow band of frequencies while leaving the frequencies outside this range relatively unaffected. They are used to remove specific frequencies, such as an annoying resonance or feedback, without significantly altering the overall sound quality.

How do audio filters work in the digital domain?

Audio filters in the digital domain process sound signals in a different way compared to their analog counterparts. Let’s dive into the distinctions between digital and analog filters and the basics of digital signal processing:

Digital filters vs. analog filters

Analog filters process continuous-time signals using electronic components such as resistors, capacitors, and inductors. In contrast, digital filters work with discrete-time signals, which are represented by a series of digital data points, typically sampled from an analog sound source.

Digital filters use mathematical algorithms to manipulate these data points, making them more versatile and precise than analog filters. Additionally, digital filters are less prone to issues such as component aging or environmental factors that can affect analog circuitry.

The table highlights the key characteristics and differences between digital and analog filters.

FeatureDigital Audio FilterAnalog Audio Filter
ImplementationUtilizes digital signal processing (DSP) algorithmsUtilizes passive electrical components
Signal QualityPreserves signal integrity and reduces noiseMay introduce noise and distortion
FlexibilityAdjustable and programmable parametersFixed characteristics
CostAffordable due to mass productionExpensive due to precision components
Size and PortabilityCompact and easily integrated into devicesBulky and requires additional space
MaintenanceSoftware updates and modificationsComponent replacement or adjustment
Frequency ResponseCan achieve precise control over frequency rangeLimited by component tolerances and design
Customization OptionsAllows for various filter types and designsLimited options based on available components
Noise ResistanceCan apply advanced algorithms for noise reductionLess effective in filtering out background noise
Durability and ReliabilityResilient to wear and tearSensitive to environmental factors and aging
A comparison of digital and analog audio filters, showcasing their respective features, advantages, and limitations

The basics of digital signal processing

Digital signal processing (DSP) is a key component in digital audio filters. DSP involves mathematical operations, such as addition, subtraction, multiplication, and division, applied to the digital data points of a sound signal. The most common DSP technique for digital filters is the use of finite impulse response (FIR) or infinite impulse response (IIR).

FIR filters implement a linear, time-invariant filtering operation on the digital data points, while IIR filters use feedback to create a more complex filtering response. Both FIR and IIR filters can be designed to perform low-pass, high-pass, band-pass, and notch filtering functions, making them powerful tools for shaping sound in the digital domain.

Common applications of audio filters

Audio filters have a wide range of applications in various fields, such as music production, audio engineering, and broadcasting. Some common applications of audio filters include:

1. Noise reduction and audio cleanup

Audio filters can help remove unwanted noise, such as hum, hiss, or rumble, from a sound signal. High-pass filters are particularly useful for eliminating low-frequency noise, while notch filters can target specific frequencies causing issues like feedback or resonance.

2. Equalization and tone control

Filters can be used to adjust the tonal balance of a sound signal, emphasizing or attenuating specific frequency ranges to create a desired sound character. For instance, low-pass filters can be applied to reduce high-frequency content and create a warmer sound, while high-pass filters can accentuate the high-frequency components, resulting in a brighter sound.

Audio filters are commonly used in speaker systems to split the audio signal into separate frequency bands for individual drivers…

3. Enhancing or isolating specific frequency ranges

Band-pass filters can be used to focus on a particular frequency range, such as isolating a specific instrument within a mix or improving the clarity of a vocal recording. Similarly, notch filters can help eliminate unwanted frequency bands that interfere with other elements in the mix.

4. Sound design and special effects

Audio filters can be employed creatively to design unique sound effects, manipulate the spectral content of sound sources, or generate interesting textures and atmospheres in music and sound design projects.

5. Crossover filters in speaker systems

Audio filters are commonly used in speaker systems to split the audio signal into separate frequency bands for individual drivers (e.g., tweeters, woofers, and subwoofers). This ensures that each driver reproduces only the frequency range it is designed for, resulting in a more accurate and efficient sound reproduction.

Image representation of sound waves. Source: pixabay
Image representation of sound waves. Source: pixabay

Popular audio filtering tools and techniques

Various audio filtering tools and techniques are available for professional and amateur audio enthusiasts, ranging from hardware devices to software applications. Some popular audio filtering tools and techniques include:

1. Digital Audio Workstations (DAWs)

Almost every DAW, such as Pro Tools, Ableton Live, FL Studio, and Logic Pro, comes with built-in audio filter plugins, offering a wide range of filter types and functionalities. These plugins can be used for equalization, noise reduction, and creative sound design within the DAW environment.

2. Standalone software plugins

Third-party audio filter plugins, such as FabFilter Pro-Q, iZotope RX, and Waves Audio plugins, provide additional functionality and advanced features. These plugins can be used in conjunction with DAWs or other audio processing software to enhance filtering capabilities and offer more precise control over the audio signal.

3. Hardware devices

Analog and digital hardware audio filters, such as equalizers, noise gates, and multi-effects processors, can be used in recording studios, live sound setups, or other audio processing environments. These devices often provide tactile controls and real-time processing, making them popular among audio professionals.

4. Modular synthesizers and Eurorack systems

These systems allow users to assemble custom audio processing chains using individual modules, including various types of audio filters. This approach provides a high degree of flexibility and control over the filtering process, enabling the creation of unique and complex audio effects.

5. Audio editing software

Programs like Adobe Audition, Audacity, and Sound Forge provide audio filtering tools for cleaning up and enhancing audio files, such as removing noise, adjusting equalization, and applying various audio effects.

Techniques for using audio filters effectively

Understanding the specific applications of different filter types and learning how to adjust filter parameters, such as cutoff frequency, resonance, and filter slope, can help users achieve the desired audio outcome. It is also essential to monitor the audio signal before and after applying filters to ensure that the changes made are improving the sound as intended.

By exploring and experimenting with these popular audio filtering tools and techniques, users can enhance the quality of their audio projects, create unique soundscapes, and tackle various audio challenges with greater confidence and precision.

If you want even more tips and insights, watch this video called “Everything You Need To Know About Comb Filtering” from the Audio University YouTube channel.

A video called “Everything You Need To Know About Comb Filtering” from the Audio University YouTube channel.

Frequently asked questions (FAQ)

Do you still have questions about what a filter is in audio? Below are some of the most commonly asked questions.

Is a filter an equalizer?

Filters only reduce (attenuate) specific frequencies in the spectrum, but equalizers can either increase or attenuate the strength of specific frequency bands in the spectrum.

How do digital and analog audio filters differ?

Analog audio filters process continuous-time signals and use components like resistors, capacitors, and inductors. In contrast, digital audio filters process discrete-time signals using digital signal processing techniques, which involve mathematical calculations on digital data, making them more versatile and precise.

Should I EQ or filter first?

If you want to get rid of evident frequency problems in your signal, use an EQ before the compressor. Only use the first EQ for cuts and fixes. Employ your filters to remove any unwanted low or high-end frequencies, as well as any unpleasant frequencies.


So, do you feel like you’ve filtered out the mysteries of audio filters? And did I cover everything you wanted to know? Let me know in the comments section below (I read and reply to every comment).

If you found this article helpful, share it with a friend, and check out my full blog for more tips and tricks on audio engineering and sound mastery. Thanks for reading, and as they say in the audio world, “May the filter be with you!”

Key takeaways

This article covered what a filter is in audio. Here are some key takeaways:

  • Audio filters selectively amplify or attenuate specific frequency ranges in a sound signal.
  • The main types of filters include low-pass, high-pass, band-pass, and notch filters.
  • Analog filters process continuous-time signals, while digital filters process discrete-time signals.
  • Common applications include noise reduction, equalization, and enhancing or isolating specific frequencies.
  • Audio filters are essential in professional audio engineering, music production, and broadcasting.
  • Popular audio filtering tools and techniques can improve audio quality and tailor sound to specific requirements.

Helpful resources

Image Andrew Ash
Written by Andrew Ash, Staff Writer

Hey there! My name is Andrew, and I'm relatively new to music production, but I've been learning a ton, and documenting my journey along the way. That's why I started this blog. If you want to improve your home studio setup and learn more along with me, this is the place for you!

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