Restoring audio depends on the actual waveform used, how it was originally created and what you plan on doing with it afterwards. This basic tutorial only scratches the surface; other subtle nuances of this art require more in-depth discussion and experimentation. But here's a good start.

From time to time, we all find ourselves with audio that’s over-maximized or suffers from clipping from field recording hiccups, inexperienced clients or other unaccountable reasons. For example, I recently received a 16-bit, 44.1 kHz. WAV recording from a friend with just these problems. You’ll notice that it’s clipping on the VU meter; it’s also quite harsh to the ears when you press Play. I can tell just from the constant loudness and over-maximized meters that the dynamics on this recording are little to none.

Next, select the Detect Clipping tool located in the Tools menu to see what you’re working with. The presets should work for most situations like this. I used [sys] Detect all 0dB clipping preset. After pressing OK, you will see the playlist markers in orange. This gives you an idea of where the most noticeable and dangerous clipping points are.

Next, select the Clip Peak Restoration tool in the Tools menu. Again, a preset will work nicely, with just a little tweaking. I used the [sys] -6dB without limiter preset, and then nudged the attenuation up to -3dB to keep as much of the original source as possible. However, I chose not to use the limiter so I could keep the source as dynamic as possible. After pressing OK, you’ll notice an enormous visual difference. The meters now have more space and dynamics.

To clean up the track and view, you can clear the clipping markers. Click Special>Clear to remove those orange markers. Since the clipping peaks have been removed and restored to a more manageable size, you don’t need them. Keep in mind that the markers are mostly there to help you with "problem regions" in the audio for more automated forms of cleaning up audio with envelopes.

You’ll notice a few left-over "scragglies" (spikes) here and there in the waveform. We now want to smoothly bring up the volume again without resulting to the previous over-maximized state, preserving a smoother sound that is less harsh on the ears and speakers. Click the DX Favorites>Mastering Effects Suite>Mastering Limiter tool. I used the [sys] Smooth Limiting preset because it’s subtle and not overpowering but will still yield the results we need in cleaning up the final waveform. You can change how much character or threshold you need, depending on your wave file. Now you’ve achieved loudness with dynamics intact!

While not absolutely necessary to this tutorial, it’s helpful to note that there is an even flow of audio data in the final processed waveform. Select View>Spectrum Analyzer. I picked 2,048 resolution and real-time view. The bars show me a consistent signal throughout the waveform, with no "harshes" (spikes) or inconsistencies.

You can now use this track in a session file with mix automation or just burn it to CD. Although this recording didn’t require it, you could choose to go -6 dB and add other iZotope effects before the main limiter (EQ, Multi-Band, Reverb, etc.).

Justin Lassen
Symphonist/Composer/Producer/Remix Artist

Justin Lassen is an accomplished dark classical composer, producer and remix artist with over 10 years’ experience in the video game, music and film markets. He’s a longtime user of Sound Forge, as well as Sony Acid Pro 6.0, Sonar 6.2 Producer Edition, FL Studio 7 XXL, and Project5 2.5. He has produced remixes for such artists as Madonna, Garbage, Blue Man Group, Lenny Kravitz, Robert Miles, Majandra Delfino, Nine Inch Nails, Linkin Park, Evanescence and Tweaker, and has worked on various projects for game and technology companies such as Interplay, Novus Delta, Cakewalk, Intel and Carbon6. In 2003, he released the critically acclaimed chamber suite, And Now We See But Through A Glass Darkly.

Restoring audio depends on the actual waveform used, how it was originally created and what you plan on doing with it afterwards. This basic tutorial only scratches the surface; other subtle nuances of this art require more in-depth discussion and experimentation. It’s best to tweak the settings that fit the wave you are trying to fix or limit. Also, always trust your ears. I chose -3 dB for the attenuation in Step 3. If you choose -6dB or more, however, you can add on more coloring or mastering effects within the iZotope suite of audio plug-ins or any others you have installed on your system.