Clean Audio: Remove Noise & Hum

Hello! Welcome to the first lesson in our new module, "Audio Post-Production: Dialogue and Cleanup." In the previous module, we focused on refining the visual edit—polishing pacing, maintaining continuity, and fixing technical issues like shaky footage. Now, we're shifting our attention from what the audience sees to what they hear.

Poor audio can ruin an otherwise great video. A distracting hum, hiss from an air conditioner, or wind noise can pull your audience right out of the story. For the short films and YouTube content you want to create, clean, clear dialogue is non-negotiable.

Your learning outcome for this lesson is to remove background noise and hum using audio editing software. We'll start with the simple tools you might already know, then graduate to more powerful, precise techniques using dedicated, free software. We'll cover two main types of unwanted sound:

Broadband noise: Constant, widespread noise like hiss, fan noise, or air conditioning.
Tonal noise: A specific, steady-pitched sound like an electrical hum or a high-pitched whine from electronics.

1. The One-Click Fix: Simple Noise Reduction

Since you have experience with CapCut, you might have already seen its noise reduction feature. It's a great example of a simple, automated tool designed for speed.

CapCut Noise Reduction Feature — This image from the CapCut interface shows its 'Noise reduction' feature. It's a single toggle switch that applies an automatic algorithm to reduce background noise in your clip.

This kind of tool is fantastic for a quick fix on a YouTube video. It analyzes the audio and tries to identify and remove noise automatically. However, this simplicity comes with a trade-off: you have no control. Sometimes it works well, but other times it can make the dialogue sound muffled, watery, or create strange digital artifacts. When the automatic fix isn't good enough, you need more specialized tools.

2. Graduating to a Dedicated Audio Editor

While video editors like Shotcut and CapCut are great for cutting picture, their audio capabilities are often limited. For professional-level audio cleanup, we turn to a Digital Audio Workstation (DAW). One of the most powerful and popular free DAWs is Audacity.

This article explains why using a dedicated audio editor is so important and, crucially, how you can create a simple workflow between Shotcut (which you know) and Audacity.

How to Use Audio From Shotcut in Audacity

The article 'How to Use Audio From Shotcut in Audacity' makes a strong case for using specialized audio software and shows you how to build a practical workflow.

Please read the following sections: 'What Makes Audio Transfer Between Programs Essential' and 'Why Standard Video Editors Fall Short for Audio': Focus on the key advantages of dedicated audio software. 'How to Extract Audio Files from Shotcut Projects': This gives you the practical steps to get your audio out of your video project. Pay attention to the recommendation of using the WAV format. 'Importing and Setting Up Audio in Audacity': This shows you how to bring your audio into Audacity.

The key takeaway is that you can do your video editing in Shotcut, export the audio as a high-quality WAV file, clean it up in Audacity, and then bring the improved audio back into your video project. This gives you the best of both worlds.

3. Removing Constant Background Noise (Hiss, Fans)

Now that we have our audio in Audacity, let's tackle the most common problem: constant background noise. Audacity has a powerful two-step tool for this called Noise Reduction.

The official Audacity support documentation provides a clear, step-by-step guide.

Noise reduction & removal

The 'Noise reduction & removal' guide from the Audacity support team provides concise instructions for its main noise cleanup tools.

Please read the first two sections, 'Noise Reduction' and 'Noise Gate'. Focus on understanding the two-step process for Noise Reduction (getting a profile, then applying) and the fundamental difference between what a Noise Gate does versus Noise Reduction.

Let's summarize the core workflow for the Noise Reduction effect:

Select a "Noise Profile": Find a few seconds of your recording that contains only the background noise you want to remove (no dialogue). Highlight this section.
Get Noise Profile: Go to Effect > Noise Reduction and click "Get Noise Profile." You've just taught Audacity what the unwanted noise sounds like.
Apply to the Entire Track: Now, select the entire audio clip (or the parts with dialogue you want to clean). Go back to Effect > Noise Reduction.
Adjust and Preview: Before clicking OK, you can adjust the settings (Noise reduction (dB), Sensitivity). A crucial tip is to toggle the "Residue" radio button. This lets you hear only the sound that is being removed. Listen to the residue to make sure you're not cutting out parts of the dialogue. It's better to leave a little noise than to damage the voice. When you're happy, switch back to "Reduce" and click OK.

The Noise Gate works differently. Instead of removing noise from the entire signal, it acts like an automatic volume switch. It drastically lowers the volume whenever the sound drops below a certain level (i.e., during pauses in speech). This is excellent for removing low-level noise that is only noticeable when no one is talking.

4. Removing Specific Background Hum (Electrical, Tonal)

Sometimes, the problem isn't a general "hiss" but a very specific, tonal sound like the 60 Hz hum from electrical wiring or a high-pitched whine from a monitor. For this, Noise Reduction is too broad a tool. We need something more surgical: a Notch Filter.

A notch filter allows you to target and remove a very narrow band of frequencies without affecting the rest of the audio.

Notch Filter Application for Hum Removal — This diagram illustrates the function of notch filters. The top shows a signal passing through filters set to 60 Hz, 120 Hz, and 180 Hz. The middle graph shows the result: sharp "notches" or dips in the frequency response, effectively cutting those specific frequencies. The bottom graph shows the original signal with clear peaks at those hum frequencies.

This video demonstrates how to find the exact frequency of a hum in Audacity and remove it with a Notch Filter.

Notch Filter Another Tool in our Toolbox

The video 'Notch Filter Another Tool in our Toolbox' provides a great practical demonstration in Audacity.

Watch from the beginning to 06:10. The presenter explains what a notch filter is for, how to use Audacity's 'Plot Spectrum' tool to find the exact frequency of an unwanted hum, and then how to apply the Notch Filter effect to remove it.

The process is as follows:

Analyze the Noise: Select a section of audio with the hum and go to Analyze > Plot Spectrum.... This will show you a graph of all the frequencies in your selection. Look for a distinct spike—that's your hum. Hover your cursor over it to see the exact frequency (e.g., 60 Hz).
Apply the Notch Filter: Select the audio you want to fix, go to Effect > Notch Filter..., and enter the frequency you just found. The Q factor determines how wide the "notch" is; a higher Q value is narrower and more precise. Apply the effect.
Check for Harmonics: As the diagram and video mention, hum often has harmonics (multiples of the base frequency). If you remove a 60 Hz hum and still hear a fainter version, you may need to apply the notch filter again at 120 Hz, 180 Hz, and so on.

Test your understanding!

You've recorded a podcast interview in a cafe. When you listen back, you can hear both the constant hiss of the espresso machine and a low, steady hum from a refrigerator. You decide to clean this up in Audacity.

What two different tools would you use to address these two separate problems, and what is the first step you would take for each tool?

Show answer

For the refrigerator hum (tonal noise): You would use the Notch Filter. The first step is to select a portion of the audio containing the hum and use Analyze > Plot Spectrum to identify the specific frequency of the hum.
For the espresso machine hiss (broadband noise): You would use the Noise Reduction effect. The first step is to select a few seconds of audio that contains only the hiss and use the "Get Noise Profile" function to teach Audacity what noise to remove.

5. An Integrated Workflow: A Glimpse into DaVinci Resolve

While using Shotcut and Audacity together is a powerful free workflow, some professional software, like DaVinci Resolve, integrates all these tools into one application. Its audio page, "Fairlight," is a full-featured DAW.

Watching how these tools are used in Resolve can help solidify the concepts, as you'll see the same principles we just discussed being applied.

DaVinci Resolve for Beginners - Remove BACKGROUND NOISE for Clean AUDIO (Free & Studio)

This video, 'DaVinci Resolve for Beginners - Remove BACKGROUND NOISE', shows how different noise reduction techniques are used and combined within a single program. Notice how the tools map to the concepts we've learned.

Watch the following segments, focusing on the type of tool being used for each problem: EQ for Wind Noise (01:06 - 02:40): The presenter uses an EQ (Equalizer) with a high-pass filter to cut out low-frequency rumble. This is conceptually similar to a targeted filter, like our notch filter but for a broader low-end range. Expander/Gate (04:56 - 08:15): This is the same as the Noise Gate we discussed. Notice how it's used to reduce noise in the quiet parts between words. Noise Reduction (09:36 - 11:20): This is Resolve's version of Audacity's noise reduction tool, where it learns a noise profile. Combining Techniques (20:06 - 23:04): This is the most important part. See how the editor stacks multiple effects (EQ, Expander, Voice Isolation) to get the best result. This shows that noise reduction is often a multi-step process, not a single fix.

Conclusion

You've now taken your first and most critical step into the world of audio post-production. Knowing how to effectively remove unwanted noise and hum is a fundamental skill that will dramatically increase the production value of your films and videos.

Key Takeaways:

For serious audio cleanup, it's best to export your audio from a video editor (like Shotcut) and use a dedicated audio editor (like Audacity).
Use Noise Reduction for broad, constant background noise like hiss or air conditioning by first providing the tool with a "noise profile."
Use a Notch Filter for specific, tonal noise like electrical hum by first identifying the exact frequency with a spectrum analyzer.
Use a Noise Gate or Expander to reduce low-level noise during silent passages.
Effective noise reduction is often a process of combining multiple tools subtly. Always listen carefully to avoid over-processing and damaging the dialogue.

Next Lesson Preview:
Now that we know how to remove unwanted noise from our recordings, what's next? The next step is to shape the sound of the dialogue itself to make it clearer and more pleasant to listen to. In our next lesson, you will learn how to apply equalization (EQ) to enhance clarity and reduce muddiness in dialogue.