Master Class: Bits and Pieces: Composite Vocal Tracks

May 1, 2009 12:00 PM, By Michael Cooper

           
 

CREATING COMPOSITE VOCAL TRACKS USING BUTT SPLICES, FADES, AND CROSSFADES

Most of the hit records of the past couple of decades owe their winning lead vocals to composite-editing techniques. For those unfamiliar with composite editing, this essentially involves recording multiple takes of a vocal performance and then combining the best parts from each take into one composite, or comp, take. This creates a superior vocal track where every line is the very best that the singer is capable of delivering.

FIG. 1: Many times, a vocal comp for a 3-minute song will have scores of edits.

For example, you might choose take 2 of a vocal track as your best overall take. Let's suppose the first and third lines of the first verse were sung great on this take, so you leave them intact. The second and fourth lines sucked, however, so you need to replace them with parts of other takes where those lines were performed better. You copy and paste the second phrase from take 5 and the fourth phrase from take 6 into take 2 at the same points in the song's timeline at which they originally occurred. Now all four lines of the first verse in the edited take 2 rock!

This technique can be used throughout a song to build a vocal comp where every line is the best it can be. But why limit yourself to pasting entire vocal phrases? You can also paste a single word or syllable or even one vowel or consonant. This might seem like overkill at first, but an emotive growl on a vowel sound in an otherwise flawed take can be pasted into a comp take to bring a phrase to life. On a 3-minute song, it's not uncommon for me to paste together more than a hundred pieces of multiple vocal takes to build a vocal comp, sometimes resulting in four or more edits on a single line (see Fig. 1).

Some DAWs offer highly useful features that streamline the process of copying and pasting together a comp track (see the review of MOTU Digital Performer 6.02 in the April 2009 issue, available at emusician.com). This functionality is a godsend for quickly assembling the best parts from multiple takes. The challenge, however, is to make all the transitions from one audio region to the next sound as transparent as possible, without any pops, clicks, abrupt changes in volume, dropped consonants, or other unnatural artifacts ruining the flow.

FIG. 2: The leading Soundbite of this butt splice ends with zero amplitude. But because the following Soundbite’s amplitude is not zero at the splice point, an instantaneous jump in level occurs, causing a click.

In this article, I'll show you how to choose the best splice points for joining two audio regions together for a seamless performance. I'll also discuss the art of applying a crossfade to a butt splice (two audio regions assembled together so they are contiguous) to eliminate artifacts at the splice point. The focus here will be on comping lead vocals, but many of the same techniques can also be used for comping background vocals and instrumental tracks.

I'll start with the basics but progress quickly to tips even experienced DAW users should find helpful. I'll use Digital Performer 6 (DP6) to illustrate my points, but most DAWs can be used to execute the same basic techniques.

What's Wrong with My Butt?

FIG. 3a: This vocal’s waveform at the splice point is whipsawed from a negative direction in phase to a positive direction at the zero crossover point, causing a click. The steep slopes and high amplitude crests immediately to either side of the splice point make an audible click more likely to occur.

Indiscriminately joining two audio regions (or Soundbites, in DP's parlance) together to form a butt splice can cause a pop or click at the splice point (the common, adjoining edge at the transition point) between them. As a Soundbite's waveform progresses from positive to negative amplitude and vice versa, it passes through a zero-amplitude crossover point where it is — for a tiny fraction of a millisecond — dead quiet. If one or both of two Soundbites are not at their zero crossover points (and silent) where they are joined, an instantaneous level change happens (see Fig. 2). The resulting square wave creates a click or pop.

After you paste two Soundbites together in your comp take, zoom the waveform display down to the sample level. Use DP's Roll tool to drag the splice point to the right or left as needed until you find a spot where the amplitude of both Soundbites is zero.

FIG. 3b: Although the phase trend at the splice point reverses from positive to negative, the amplitude crests and slopes of the two waveforms to either side of the splice point are mild enough that an audible click doesn’t occur.

Finding a common zero crossover point may not be enough, however, to avoid creating a pop or click. Often you must choose a point where the phase of both Soundbites is trending in the same direction. For example, if the leading Soundbite is transitioning from positive to negative amplitude at the splice point, the following Soundbite should be as well; in this case, a click or pop will often occur if the following Soundbite immediately trends toward a positive amplitude. A click is most likely to occur when the slope of both waveforms at the splice point is very steep (indicating high-frequency content) and the immediately preceding and following amplitude crests are high (indicating loud volume). Conversely, you can often get away with opposing phase cycles at the splice point when both waveforms are low amplitude and gently sloping (see Figs. 3a and 3b).