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Thursday, July 06, 1995

On The Level

Techniques for mixing layers of audio with maximum clarity.

Admit it: How many of you mix audio by dragging the music, narration, and sound effects or ambiance bed into your authoring program...and think you’re finished? Okay, you don’t, but I’ve heard numberous television programs and pieces of interactive media that sound that way. Each component might sound fine individually, but when more than one is playing at the same time, they obscure each other. Or maybe during quieter sections, an unacceptable amount of noise or distortion appears when played back on a system with lower bit-depth or compressed audio. The solution to both comes from proper management of audio levels.

Note: This article was originally written in the days of CD-ROMs with 8-bit audio, and shows examples using an early version of Adobe Premiere, but virtually all of the concepts remain valid today with all types of media involving the combination of audio and video - including compressed web delivery.

Duck!

Meyer’s Law of Multimedia Mixing: The sound effects should not dominate the music, and the music should not dominate the narrator. Since you can’t expect this to happen (super)naturally, you’ll need to adjust their respective levels to make it happen. Let’s look at a couple of mixes:

A typical beginner’s mix, where the volumes (the horizontal lines under the waveform displays) are all left at their default 100% volume settings. (Click here to open a higher resolution verison of this figure.)

A more refined mix, where audio elements build in stages, and the volume of less important tracks is reduced when more important tracks enter. (Click here to open a higher resolution verison of this figure.)

The first figure above shows the “everybody’s equal” approach to mixing, while the second figure shows a more balanced mix. An ambiance bed on track three sets up the scene, akin to how the background image sets the mood. Rather than coming on at full volume, it is faded up just as frames are dissolved on. Indeed, it is a good idea to make the duration of the fade match that of the dissolve - this will further lock in the pace as well as the feeling that “we’re changing scenes now...”.

Next, the music starts on track two. The ambiance bed starts to fade down shortly after the music starts - this way, the fade does not draw attention to itself, but still gets the ambiance out of the way. I’ll tend to keep the ambiance bed playing at a low level in the background, and then fade it up again after the music and narration stops. Keeping it around can also serve a useful function when playing back on a computer with 8-bit audio (we’ll get to that later).

Next comes the narration. Notice that the music fades down before the voice starts - this way it does not obscure any of the words, and subtly cues the listener that something new is about to happen to pay attention to. This technique is often referred to as “ducking” - the music ducks out of the way of the incoming voice. Whatever your production may be - CD-ROM, radio, TV, or any situation where voice and music appear together and the voice is supposed to take the lead - remember to duck the audio out of its way.

Audio • Editing • Post Production •

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