[ This article was first published in the October, 2008, issue of
Larry’s Final Cut Pro Newsletter. Click here to subscribe. ]
One of the exciting features in Soundtrack Pro is its ability to reduce background noise.
Notice that I said “reduce,” not eliminate. If you need to remove a sound, you’ll need to re-record the audio. If, on the other hand, you just want greater separation between your speaker and the background, this tool can do the trick.
Here’s the basic problem we have with noise reduction: the normal human ear hears frequencies between 20 cycles per second and 20,000 cycles per second. 20 cycles is so low it feels more like a vibration, while 20,000 cycles is so high, it sounds more like the wind in pine trees. Every voice, sound, piece of music, or noise falls within that range of cycles. This means that many noises overlap voice frequencies. If we remove all of the noise frequencies, we also remove parts of the voice frequencies, creating very strange, and generally unpleasant, effects.
So, our goal is to isolate as much of the noise as we can and remove it without doing major damage to the voice. While all noise is different, and no two clips will have the same values, the process of reducing noise is the same.
Here’s the process.
1. If your clip is already edited into the Timeline in Final Cut, select it and choose File > Send to > Soundtrack Pro Audio File Project.
2. In the Send dialog, give the file a name and store it in your Final Cut Projects folder. This will become a permanent part of your project and will be needed for final output. The rest of the defaults are fine. Click OK.
Note: You can repair audio either as an audio file project or by selecting a clip in a multitrack mix and choosing the File Editor tab in the Lower Pane. Regardless of which you choose, the noise reduction process is the same. In this example, to make the screens easier to read, I’m using an Audio File project.
3. After listening to the clip, drag across the waveform to select a portion of the clip that only contains the noise you want to remove; it should not contain any of the sounds you want to keep. Select Process > Noise Reduction > Set Noise Print. This samples the noise and stores it into a special clipboard within Soundtrack Pro.
4. Next, select the portion of the clip that you want to remove the noise from. Selection can be done by dragging, or double-clicking to select between markers, or pressing Command+A to select the entire clip.
5. Choose Process > Noise Reduction > Reduce Noise. This opens the Noise Reduction HUD (heads-up display) that allows you to fine tune your settings to remove the noise. This dialog works from the top to the bottom. Press the right-pointing arrow to start playback.
6. Slowly drag the top slider to the right and listen carefully until the noise is gone. Here the noise was gone when we reached -29.6 dB. At the same time, you’ll notice that the voice of the speaker starts to sound hollow, electronic, or “Darth-Vader-y”. Not to panic.
7. To get the speaker’s voice to sound normal, move down to the second line and drag the slider to the left. You’ll hear two things: first, the speaker’s voice starts to sound human again and, second, some of the noise returns. This is generally unavoidable — that’s why we call it noise reduction, not noise removal. Stop when the voice sounds “normal” to you. In this case, we stopped at 76%. This means that we have removed 76% of the original noise. Press the right-pointing arrow to stop playback.
8. If you want a voice to sound warm, inviting, and sexy, you boost the bass. If you want a voice to sound clear and intelligible, you boost the treble. That’s because vowels are low frequency sounds and provide the voice its character. Consonants, on the other hand, are high-frequency sounds and provide the voice its diction and clarity. In our case, we want to make sure people understand what is being said, so I’ll preserve some of the treble.
9. Click OK and watch as the waveform shrinks as the noise is removed. Play the noise-reduced section and congratulate yourself on salvaging this audio.
10. To get it back into Final Cut simply choose File > Save. If you are doing this in a multitrack project, the changes are saved with the clip and will output during your final export.
That’s it. Once you understand the process, cleaning up your audio is both quick and easy.
Final note: Whenever you remove noise, you are also removing voice frequencies. This means the speaker won’t sound as good as the original clip. Sometimes the quality change is not noticeable, other times it is. In each case, you need to decide whether the improvement in intelligibility outweighs the loss in quality. If you remove noise carefully, you’ll find that in most cases, the answer is yes.
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