Recording Vocals, Part 5: Adding Effects to Vocal Tracks

By David Franz

Over the past several months I've discussed recording, editing, and mixing vocal tracks in Pro Tools. We've gone over methods for capturing the best sound, getting the best possible performance, editing the best parts into one solid, emotive performance, and using EQ to get the best vocal sound. However, there are still more techniques you can use to make your vocal tracks sound impressive. Picking up where we left off last month, let's jump right into some more mixing techniques for vocal tracks.

Smoothing Out Performances with Dynamic Processing
Dynamic processing (compression, limiting, gating, and expansion) adjusts the dynamic range of a track by altering the volume relationship between the loudest and softest parts of the track, helping the track to have a more consistent sound and level in a mix. Two of the more common dynamic processing effects used on vocal tracks are compression and its more extreme brother, limiting.

Compression and limiting are used on vocal tracks to smooth out the transients in the performance, keep the level steady, and help the vocals sit comfortably within or slightly above the other instruments in a mix. Common compression techniques for vocals usually include peak limiting, light constant compression, and squashing. I discussed the techniques of using compression and limiting in my June 2003 DigiZine column about mixing guitar tracks, so I won't restate it here. The same concepts and similar techniques for compressing and limiting guitar tracks apply to vocals.

Opening the Gate
Another technique for dynamic processing on vocal tracks is gating. Gates allow an audio signal to pass through them if the signal is above a specified threshold. When the signal is below the threshold, the gate closes, attenuating the signal partially or fully. Gates are utilized to allow the desired (louder) signal to pass through to the output while denying unwanted (softer) signals. They're useful for eliminating unwanted noise on tracks (like headphone bleed or even the singer's breathing), for creating cool effects like cutting off reverb tails, and many other applications.

	Figure 1: A DigiRack Gate plug-in with parameters for eliminating headphone bleed on a vocal track.

What happens when a signal comes into a gate? First the gate inspects the signal and decides if it's above the specified threshold level. If the threshold hasn't been crossed, the gate remains closed and blocks the signal from going to the output. However, if the signal crosses the threshold, the gate opens up according to the attack speed parameter. The gate stays open for a specified amount of time (the hold time) and then closes after the signal has fallen below the threshold volume, at the speed selected in the decay parameter.

The range parameter on a gate determines how much the volume is reduced on a signal that moves below the threshold. The lower the range value (for example, –80 dB), the less volume the gate allows to pass through on signals below the threshold. Gates with medium to high range values (–40 to 0 dB) are called "expanders." For more information on expanders and other dynamic processors, please refer to my book Producing in the Home Studio with Pro Tools (2nd Ed.).

Some notes for using gates on vocal tracks:

1. Fast attack times are usually necessary when gating percussive vocal tracks so that the initial transients aren't gated.

2. Short release times may unintentionally cut off the ends of notes. Use longer release times for more gradual fades.

3. Each time you add a gate to a vocal track, be sure to listen to the track closely (both in solo and in the mix) to ensure that the gating is smooth and no vocal lines are inadvertently gated out of the performance.

Creating a Listening Environment with Depth Processing
Where dynamic processing deals mainly with volume levels, depth processing deals with creating an environment. Depth processing (reverb and delay) utilizes sound reflections and repeats to add spaciousness to vocal tracks. Using reverb and delay in a mix tricks our minds into thinking that the vocals are coming from a larger or more interesting environment by creating repeats (reflections from the surrounding environment) that combine with the original sound. Short repeat times characterize small acoustical spaces, while long delays give the aural illusion of largeness.

More complicated than simple delays, reverb is a complex combination of blended delays that simulate an acoustical environment (like a small wood-paneled room, sports arena, or jazz club). We'll cover reverb in this month's column and tackle all the different types of delay (echo, slapback delay, doubling, chorus, flange, and phase shifting) next month.

Finding the Space
All acoustical spaces (rooms, halls, etc.) have their own sound. The unique sound of a space is created by the combination of reflections and absorption from its surfaces: walls, floor, ceiling, and objects. Each individual reflection is a delayed and slightly altered copy of the source sound. When a large number of these reflections are added together and we can't distinguish between the individual signals, they all blend together to form reverb (reverberation). Some reverb sounds are created to imitate acoustical spaces (like halls and rooms) and others simulate plate and spring reverbs (which originally were intended to imitate halls and rooms, but eventually took on a sound of their own).

When a sound is made, we hear several different things: the direct sound waves, the early reflections, and the reverberation (a.k.a. "after reflections" or "dense reflections"), in that order. The direct sound reaches our ears without bouncing off any surface. Early reflections reach our ears around 10-30ms later than the direct sound, after they have bounced off one or more surfaces. Because these reflections arrive so quickly, they are perceived as part of the direct sound. Reverberation actually occurs when a sound reflects off many surfaces and is mixed with other reflections, creating a denser blend of reflected sound. These reflections begin to fade away (decay) as they're absorbed into the material of the acoustical space. The longer a sound takes to decay, the larger (and more hard-surfaced) the acoustic environment is perceived to be, and the farther from the sound source the listener is (or seems to be).

Reverb Relationships
The amount of reverb and the decay time of the reverb have these five basic relationships:

Tweakin' the 'Verb
When applying reverb to vocal tracks, the wet/dry mix parameter sets the overall amount of depth processing — how far away the voice is from the listener. In addition to the decay time, the longer the predelay time (the time before reverb is heard), the larger the perceived size of the acoustical space. Predelay is often one of the first parameters I tweak when choosing the size of the reverb sound.

In concert with the size parameters, reverb often sounds more impressive if used in stereo. Many plug-ins and outboard effects processors allow mono in/stereo out reverb processing, enabling you to simply pan out the reverb returns for a wider stereo image. For example, Digidesign's new ReVibe plug-in has a Stereo Width parameter that allows you to specify how wide the reverb stereo image is, giving you full control over how large your reverb space sounds in your mix.

Figure 2: Digidesign's ReVibe reverb plug-in with a "Bright and Airy Hall" reverb setting. Notice the parameter names and values for this setting. This plug-in also includes many EQ parameters that affect the "color" of the reverb sound. Click to enalrge

Although big reverb settings sound impressive, consider using low-pass and/or high pass filters on your reverb (or in addition to your reverb) to tighten up the frequency range of the reverb output. With plug-ins like ReVibe, you can use the built-in "color" parameters for this purpose. EQing your reverb can seriously help to clarify your mix and help you avoid unwanted frequency buildups — too much reverb can make your mix sound less defined, and have less impact.

Also, listen carefully to your favorite artists and figure out what types of acoustical spaces the mix engineers are putting the listener into. Along with listening, study the reverb parameter definitions by physically tweaking some tracks through different reverb settings. This kind of "research" is very valuable, and can lead to developing a new approach. Combining techniques from current trends with all your old favorites can help you develop your own knowledge of reverb and your own mixing style.

Wrap-Up
Dynamic and depth processing are two of the primary ways to improve the sound of your vocal tracks by adding effects. Join me next month as I delve deeper into depth processing, including all the flavors of delay. I'll also provide some examples that combine all the vocal mix techniques we've covered so far. See you soon. Peace.

Like what you see in this column? Check out my book, Producing in the Home Studio with Pro Tools (2nd Edition). You can buy it online right here through Digidesign's web store, or visit www.protoolsbook.com. Interested in personal instruction on Pro Tools from yours truly? Visit www.berkleemusic.com and learn about several amazing Pro Tools learning experiences available online though Berklee College of Music. Wanna see my studio and hear some samples of my work? Visit www.undergroundsun.com.

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