Editors often work with interview clips recorded on location that have ambient noise underlying and competing with the interview track. Audacity’s Noise Reduction effect can reduce moderate amounts of ‘hiss’ (HVAC noise) or constant background sounds such as hum, whine or buzz (computer generated noise). Please note that this effect works best when the interviewee is properly mic’d and when the recorded voice is significantly louder than the ambient sound you are trying to remove. Noise Reduction is not suitable for irregular background noise such as traffic or crowd noise.
1. In your editing application, export an audio only WAVE file of your video interview.
2. Launch Audacity and drag and drop your WAVE file into the empty Timeline track. Choose Make a Copy of the Files Before Editing and click OK.
3. Zoom into the Timeline using the Zoom Tool. Use the Selection Tool and with your cursor, drag out a section of the audio waveform that contains only the noise you want to remove. The larger the sample, the more effective the noise reduction will be.
4. Go to Effect > Noise Reduction > Step 1. Click Get Noise Profile. This identifies the different frequencies of the noise you want to remove.
5. Select the entire interview clip (or a region of the waveform) that you want to reduce noise from.
6. Go to Effect > Noise Reduction > Step 2 and set the Noise Reduction parameters.
Noise Reduction controls the amount of volume reduction to be applied to the noise. For light noise, adjust this parameter between 12 and 15dB to reduce the noise but maintain the integrity of the interview audio.
Sensitivity controls how much of the audio will be considered as noise on a scale of 0 to 24. Set this control to a value that will effectively reduce noise without distorting the interview audio.
Frequency Smoothing can reduce the perception of noise artifacts by spreading them out over one or more frequency bands. This parameter is best set to a value between 0 to 6.
Adjust the sliders and click the Preview button to listen to the audio with the noise reduction effect.
7. When you have found settings that best reduce the ambient noise without distorting the interview audio, click thebutton then click to apply the effect.
8. Playback your audio and undo and redo noise reduction to listen to before and after the applied effect.
9. Export your file in a WAVE format and import and sync it to your original file in your editing application. Lower the volume of the original audio to 0dB.
Written by Kate Lee, Senior Media Producer
Credit: Audacity Development Manual