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TUTORIAL: Noise Reduction in Adobe Audition
Posted Sep 5, 2006 Print Version     Page 1of 1

Many times during our video shoots we get persistent, intrusive noises that are outside of our control and need to be cleaned up. Sometimes these noises are AC ground-related; other times it's the hum of an air conditioning unit.
     The fact is that no matter how well you have placed your mics or how good your equipment is, sooner or later you will be faced with the challenge of cleaning up your audio.
     Adobe Audition, which is included with Adobe Production Studio Premium, lets you do that quickly and efficiently with the Noise Reduction effect.

Step 1: Bringing in the Clip
The first step to this cleanup process is to bring the clip into Audition. If you bring in a video clip, Audition can work on the audio portion only. You could also bring in just the audio clip after separating the audio from the video in Premiere Pro or whatever editing application you happen to be using.

To import the audio file into Audition, choose File > Import, or use the keyboard shortcut Ctrl + I. You could also use my favorite method of bringing files into some Adobe applications, which is to double-click on the Project Panel and thus open up the Import File dialog box.

The particular piece we'll use as an example in this tutorial has AC ground noise that I can clearly hear. To get accustomed to working with noise reduction in Audition, you should find an audio clip that contains an even, constant unwanted noise throughout the clip.

To start processing the file, you must first double-click it so that it opens in the editing mode. In order to remove the noise, you need to "tell" Audition what the noise is. Select and highlight only the unwanted noise.

Step 2: Identifying the Noise
Isolating only the noise can sometimes be challenging because, by default, Audition will show you the waveform for the entire clip. If you have a clip that is an hour long but the noise only lasts a couple of seconds, then your view of the clip will be too wide to accurately select only the noise. If this is the case, you need to zoom in. The shortcuts to zoom in and out are the plus (+) and minus (-) keys on your keyboard. You must zoom in enough so that you're close enough to choose only the noise in your affected audio and nothing else.

With many of the audio files that you will bring into Audition, you will be able to clearly distinguish the noise from the audio that you want to keep in the waveform that Audition displays. The noise will usually be a low waveform that is fairly uniform in its shape. Any parts of your audio clip that at first do not appear in waveforms will usually be noise.

Once you've identified the section of the waveform that represents the noise, click at the beginning of a noise segment and drag until you have selected one to two seconds of only noise. Be careful that you do not select a "good" portion of your audio. Audition needs to sample only the noise in order to remove it (Figure 1).

figure 1
Figure 1. Here's Audition's waveform representation of our clip, with the low hum of the offending noise isolated so we can remove it.

Step 3: Reducing the Noise
After you've selected the noise, choose Effects > Restoration > Noise Reduction. You can also click on the Effects tab, which, by default, is "live" behind the Files panel. Then choose Restoration > Noise Reduction (Process) within that panel (Figure 2).

figure 1
Figure 2. Choose Restoration > Noise Reduction (Process) from Audition's Effects panel to open the Noise Reduction panel and get to work.

The Noise Reduction panel opens in a new window, where you will see several settings. The first thing that you need to do is locate the Capture Profile button in the upper-right-hand corner (Figure 3) and click it. This will sample the noise, and then Audition will know what to remove.

figure 1
Figure 3. Here's Audition's Noise Reduction window. The entire process of removing the noise will happen here. 

After Audition has sampled the noise portion of your audio, you need to click Select Entire Clip, which is also found on the right-hand side of the Noise Reduction window. As you might expect, clicking this button selects the entire clip; keep in mind that only the noise was selected before.

Preview the effect by locating the Preview button in the lower-right section of the Noise Reduction window and clicking on it. You can also bypass the effect while previewing by checking the Bypass box just above the Preview button. By doing so, you can compare the clip's original unprocessed sound with the noise-reduced version you just heard.

Chances are that you do not need to do anything else, and if you've successfully eliminated the noise, all you need to do is click OK, and the process will begin. Audition will do some processing, and once it's done you will be able to play your clip without the noise. Save the corrected clip by choosing File > Save, or by using the keyboard shortcut Ctrl + S.

Step 4: Making Further Adjustments
Sometimes, even if you do everything exactly the way that I just described, you will not get satisfactory results. If this is the case, you need to tweak the parameters of the effect. You do this by adjusting the Noise Reduction Level (Figure 4), which is also found in the Noise Reduction window. While previewing the sound, increase or decrease the level until the sound is optimized or the noise is minimized.

figure 1
Figure 4. Use this slider bar to tweak the Noise Reduction effect if it doesn't work when you apply it at the preset level. Live preview will assist your adjustments.

You can also choose Keep Only the Noise (Figure 5) from the lower-left section of the Noise Reduction window. This will help you know for sure what it is that Audition will remove. If you hear any kind of good audio when running this diagnostic, then you will know that you added too much of the effect and you need to reduce the noise reduction level.

figure 1
Figure 5. Chooseing Keep Only the Noise from the lower-left section of the Noise Reduction window will help you know for sure what Audition will remove.

Remember to check the Remove Noise button before you apply the effect. Otherwise, Audition will remove the good audio and keep only the noise. This setting is included so that you can hear exactly what Audition will remove.

Step 5: Creating and Using Noise Profiles
If you have a consistent noise that appears often in your recordings—maybe you shoot at a place that always has the same amount of noise—you can probably expect to encounter the same noise—at the same level—during future edits. Thus, you may want to save a profile for it that will save you some time in the future.

To save the noise profile, select the noise and apply the Noise Reduction effect (with or without the noise reduction level adjusted, depending on how much tweaking you had to do). Next, locate the Noise Profiles box in the upper right corner of the Noise Reduction window, click on Capture Profile and then Save Profile (Figure 6).

figure 1
Figure 6. To save the noise profile for future use, select the noise, apply the Noise Reduction effect, click on Capture Profile, and then choose Save Profile.

After this, all you need to do to use this feature is apply the effect and click Load from File. You will no longer need to capture the noise from the clip, since you will have it on file. Be careful, though, because even if it is the same type of noise, it may have been recorded differently, and therefore using a profile that was previously saved may not work properly.

Handling Other Noise Complaints
I will end this tutorial by adding that there are numerous ways of removing unwanted noise from your audio clips, and the Noise Reduction effect is just one of them. You can also use the Notch Effect, Restoration, and other processes.

I suggest experimenting with the different effects and different settings until you get a good feel for what does what. As with everything you do in a postproduction tool, experiment and get familiar with what produces what effect, and you will soon be using Audition's Noise Reduction effect like a pro!

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