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Filed under: Audio •Editing •Post Production •

On The Level

Rising Above the Noise

Unfortunately, keeping audio levels balanced is often just half the battle. The other half is keeping all the levels above the noise created when your wonderful creation gets played back on through a medium with low bit-depth or bit-rate sound.

You’ve already heard that you are supposed to “normalize” - maximize the signal level - of all your audio files. This helps, but sometimes the levels inside a single audio file changes so much you can’t keep the quiet segments from being described by too few bits, which results in quantization noise and distortion (see sidebar). So, you need to find ways to reduce the dynamic range of your files and keep them consistently loud. You can perform some of this manually by “riding” the audio level, as illustrated in the figures on previous pages showing the narration track. But there are other devices that can do the job automatically.

The most common audio studio devices used for this purpose are called compressors and limiters. Compressors look at any sound over a certain threshold loudness, and reduces their level. This may seem counterproductive, but what it means is that you can then raise the overall signal level without worrying as much about clipping. A more brute-force device is the limiter, which simply clamps the maximum level without clipping as you can keep cranking up the overall level.

If your original audio files were not recorded with compression or limiting applied, there are some software-only solutions. Many developers use audio software such as Adobe Audition or Soundbooth, Apple Audition, Sony SoundForge, or BIAS Peak to massage audio. Some companies such as Waves create audio plug-ins for Sound Designer. Waves in particular make a great limiter called L1; an early version of the plug-in is shown at right.

One Person’s Noise...

Another approach to reducing quantization distortion is to make sure those lower bits are always getting tickled. Some add “dithering noise” to do this. The result is less apparent distortion, but at the cost of a constant noise hissing along underneath (constant noise tends to be less objectionable and more easily ignored by the listener than pumping noise and distortion).

For me, even better is if that pure noise was replaced with something more appropriate to the visuals - such as an ambiance bed of wind, running water, etc. That’s one of the reasons I use ambiance beds in multimedia mixes: Start with a little background to set the stage, and then fade it down to where it just tickles those lower bits so that the music and voice will appear less distorted. The listener is tricked into thinking they’re still hearing an appropriate sound rather than just noise, even though that’s all it may sound like at such low levels.

So now you know my tricks for better-sounding mixes. Hopefully you can apply some of them to your next project, and make your next audio-visual presentation sound like an appropriately mixed-media one.

Article originally written in 1995 for Multimedia Producer; updated 1999, 2002, & 2008. The technology may change, but some basic concepts of what we see and how we hear don’t!

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