Audacity Low Pass Filters: Explained



Jun 17, 2023

Audacity, the popular open-source audio editing software, offers a wide range of features and tools to help users manipulate and enhance their audio recordings. 

One such powerful tool is the low pass filter. 

In this blog, we will delve into the world of Audacity's low pass filters, exploring what they are, how they work, and how they can be used to improve your audio projects.

Understanding low pass filters

Before we dive into Audacity's implementation of low pass filters, let's start with a basic understanding of what a low pass filter is. In audio engineering, a low pass filter is an equalisation (EQ) effect that allows frequencies below a certain cutoff point to pass through, while attenuating frequencies above that point. 

Essentially, this means that high-pitched or high-frequency sounds are reduced or eliminated, resulting in a smoother, more subdued audio output. This can help soften sounds that are too bright or harsh.

If you’re looking to clean up the lower ends of sound frequencies, read more about high pass filters

What does low pass filter in Audacity do?

Audacity's low pass filters allow users to cut out high-end sound frequencies (Hz) and control the impact of filtering on audio tracks. The software offers both graphical and non-graphical interfaces for working with low pass filters, allowing users to choose the method that suits their preferences and workflow.

The graphical interface presents a frequency response graph, allowing users to visualise the effect of the filter in real-time. By adjusting the cutoff frequency, slope, and resonance, users can precisely control the impact of the low pass filter on their audio tracks. This visual feedback greatly assists in fine-tuning the filtering process.

On the other hand, the non-graphical interface provides a simpler, more straightforward approach. Users can specify the cutoff frequency numerically, choose the filter type, and adjust the filter order. This interface is ideal for users who prefer a more direct and efficient workflow.

Applications of low pass filters in Audacity

Now that we understand how low pass filters work in Audacity, let's explore some practical applications where they can be beneficial:

  1. Noise reduction: low pass filters can effectively reduce background noise in audio recordings. By removing high-frequency noise components, such as hisses or hums, you can significantly enhance the clarity of your audio.
  2. Taming harsh sounds: sometimes, audio recordings can contain harsh or shrill sounds that can be uncomfortable to the listener. By applying a low pass filter, you can attenuate these high-frequency elements and create a more pleasant listening experience.
  3. Creative sound design: low pass filters can also be used for creative purposes. By selectively filtering out high-frequency components, you can shape the tonal characteristics of your audio, adding warmth to vocals or creating unique sound effects.

How to use low pass filters in Audacity

Here's a step-by-step guide on how to use the low pass filter in Audacity:

Step 1 - Import your audio: launch Audacity and import the audio file you want to work with. You can do this by going to "File" in the menu bar and selecting "Import" > "Audio." Locate and select the desired audio file from your computer, and click "Open" to import it into Audacity.

Step 2 - Select the audio track: once your audio file is imported, you'll see it displayed as a waveform in the Audacity workspace. Click and drag your mouse over the portion of the audio track you want to apply the low pass filter to. If you want to apply the filter to the entire track, skip this step.

Step 3: Access the low pass filter: in the menu bar, navigate to "Effect" and choose "Low Pass Filter" from the drop-down menu. This will open the Low Pass Filter dialog box.

Step 4: Adjust the filter settings: in the low pass filter dialog box, you'll find various parameters to customise the effect. Let's explore the essential settings:

  • Cutoff frequency: This determines the point at which the filter starts attenuating high-frequency sounds. Drag the slider or input a value in Hertz (Hz) to set the desired cutoff frequency.
  • Filter order: This determines the steepness of the filter slope. Higher filter orders result in a more pronounced attenuation of high-frequency sounds. Adjust the slider or input a value to set the filter order.
  • Rolloff: This controls the resonance of the filter. A higher rolloff value accentuates the attenuation of frequencies beyond the cutoff point. Use the slider to set the desired rolloff value.

Step 5: Preview and Fine-Tune: To preview the effect of the low pass filter, click on the "Preview" button. You can listen to the filtered audio and make adjustments to the settings as needed. Take note of any unwanted artifacts or excessive filtering that may affect the audio quality.

Step 6: Apply the Low Pass Filter: Once you're satisfied with the filter settings, click on the "OK" button in the Low Pass Filter dialog box. The low pass filter effect will be applied to the selected portion of the audio track(s).

Step 7: Save Your Filtered Audio: After applying the low pass filter, you can save the filtered audio. Go to "File" in the menu bar and select "Export" > "Export as [file format]." Choose a file name and location, select the desired audio format, and click "Save" to export the filtered audio.


Audacity's low pass filters provide a powerful toolset for audio editing and enhancement. Whether you're a professional audio engineer or a hobbyist, understanding how low pass filters work and how to utilise them effectively can take your audio projects to new heights. 

By reducing unwanted noise, taming harsh sounds, or exploring creative sound design possibilities, you can achieve the desired audio quality and deliver a captivating experience to your listeners. So, fire up Audacity, experiment with low pass filters, and let your creativity soar. To get started, why not check out our list of the best free EQ plugins?

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