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Tutorial: Fixing Clipped Audio with iZotope RX3

We've all had the misfortune of recording clipped, distorted audio from a signal that's too hot, resulting in time-consuming retakes or total disaster if the audio is from a live event. The Declip feature in iZotope RX3 can reduce that disaster to a quick and easy fix.

In this tutorial we’ll look at the de-clipping feature in iZotope RX3 Advanced.

The day before I wrote this article, I ran a webinar. During the webinar, something happened to limit the gain in my audio recording gear to the limits you see in the waveform shown in Figure 1 (below). Somewhere along the line, I imposed about a 14dB limit on the recording.

Figure 1. The limited audio levels I set inadvertently in my audio recording gear, represented in the waveform in iZotope RX3 Advanced. Click the image to see it at full size.

I use the same recording gear for the webinar that I use for my screencams. This morning, without checking my settings, I recorded a roughly 30-minute screencam, and edited it down to about 22 minutes, which was when I discovered this limitation. The problem is that anytime the audio gets close to the top and hits that limit, you’re going to hear distortion.

At the 1:03 mark in the tutorial video at the top of this page, you can hear the clipping in the file as I play back the audio. Again, anytime the peaks are flatlined, as in Figure 1, you’ll hear distortion in your audio track, and you’ll need to find some way to fix it if you hope to salvage the recording.

Running Declip

To fix this issue in iZotope RX3, select the portion of the clip you want to fix (or the entire clip), choose the Declip feature (highlighted, top right, in Figure 2, below), which opens the Declip dialog box. There I click Suggest to tell iZotope to detect the clipping threshold automatically by analyzing the waveform, and then click Process at the bottom of the dialog to apply the filter to the selection.

Figure 2. The Declip dialog in iZotope RX3. Click the image to see it at full size.

Figure 3 (below) shows the before-and-after view of the waveform after applying the Declip filter to the selected portion of the clip. You can hear the selection with Declip applied and the distortion removed at the 1:27 mark of the tutorial video above.

Figure 3. Note the change in the selected portion of the clip with Declip applied (right). No more flatlining at the peaks as before (left). 

Related Articles
In this first installment of a two-part series, Jan Ozer compares the declipping and crackle and pop-removal features in iZotope's new RX 3 pro audio editor to the parallel features in Adobe Audition CC.
In this final round between audio editing champs iZotope RX 3 and Adobe Audition CC, we compare the two audio editors in noise reduction and reverb/echo reduction.