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Fixing Advanced Audio Editing Tutorial:Noise Removal

Fixing Advanced Audio Editing Tutorial:Noise Removal

Your first line of defense for Noise Removal is the low-cut or high-pass filter. This tool is available in some form in virtually every NLE and DAW out there.

Noise: the bane of all editors. It's everywhere and comes from many different sources. We can boil them all down to two main types: constant noise and random noise. Constant noise comes from things like air conditioners, motors and transformers. Mics, mixers and cameras can add noise too. Random noise is trickier and comes from sources like nature, people and traffic. Fortunately, there are audio tools to address both types of noise. But let's be honest; it's unlikely you will eliminate all noise from your recordings, but you can minimize it to acceptable, even unnoticeable levels. Most mid-to-high range programs can do these tricks, we're using Adobe in our demo.

The Filter

Your first line of defense in noise reduction is the low-cut or high-pass filter. This tool is available in some form in virtually every NLE and DAW out there. Let's say you shot an office interview and the house air conditioning produced a constant rumble in your recording.

In Premiere, with the clip on the timeline, click on Effects/Audio Effects/Stereo and scroll down the list until you find the high-pass filter (Figure 1). Drag it onto your audio track.

In the Effects Control section, open the high-pass filter and move the control slider to the 90Hz area (Figure 2). This is a good starting point, but adjust for the best balance of noise removal and sound quality. The high-pass filter cuts off any audio signal below the control setting, and it works well for low-frequency sounds like rumble and some wind noise.

If hiss is the enemy, try the low-pass filter instead (Figure 3). Usage is similar, only this time, start the control slider in the 12,500Hz region (Figure 4). The low-pass filter cuts audio frequencies above the control setting, so now your challenge is to find the best balance of hiss reduction and crispness. The human voice doesn't carry much above this point anyway, but you have to decide on an acceptable cutoff frequency.

If your audio recording has one constant noise that's driving you crazy - like the whine of a small office refrigerator - try a notch filter instead. Usage is the same as the previous filters, only this time you have two adjustments to make. The first is Center Frequency. Tune this to the frequency area that's making you nuts - it may take a few tries to find the right spot (Figure 5). The second adjustment is "Q" and determines how wide the notch is. The lower the Q, the narrower the notch. With the right settings, this can be a lifesaver. And, as usual, the wrong settings will really mess with your audio quality.

Drastic Measures

Sometimes a simple filter isn't enough to minimize the noise effectively.

This calls for drastic measures. So it's time to move your audio to a digital audio workstation or DAW. Virtually all DAWs have some form of advanced tools - even the freeware Audacity audio editor has an effective noise reduction tool.

Export your audio to a WAV file and open it in your favorite DAW. We're using Audition here, but most editors use similar procedures. Find and highlight a section that contains only the noise. Click Effects/Restoration/Capture Noise Profile (Figure 6).

Next, highlight the entire file and click Effects/Restoration/Noise Reduction. This will open the Noise Reduction dialog box with several control options (Figure 7).

Notice the spectrogram at the top of the window. This is the snapshot of noise that you captured in the previous step. For starters, just use the preset values for now and click OK. After a bit, you'll have a de-noised file...maybe. Listen closely for strange, new noises and undo as necessary. It may take several tries - using different settings - to get it right, but this type of noise reduction is an amazing tool.

Tag Team

Getting rid of noise is a tiresome pain, but unavoidable for the audio editor. If the noises are more sporadic, consider using any of these techniques on small fragments of the audio rather than the entire file.

Depending on the noise you need to remove, your best results may be from a combination of techniques; filter first, then de-noise the remainder. It's really up to you, your project and the amount of noise that's bothering you. Dig into your audio and video software to find all the options and try them out. If it doesn't work the first time, undo and try another method or different settings. Noise removal tools and techniques are widespread and easy to use. Find the ones that best suit your project and get rid of that noise!

Contributing Editor Hal Robertson is a digital media producer and technology consultant.

Tags:  November 2009
Hal
Robertson
Sun, 11/01/2009 - 12:00am