Recording Vocals, Part 6:
Adding Ambient Effects to Vocal Tracks

By David Franz

Over the past several months I've discussed techniques for recording, editing, and mixing vocal tracks in Pro Tools: capturing the best sound, encouraging vocalists to give their best performance, editing the best parts into one solid, emotive performance, and using EQ, compression, and reverb 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, let's jump right into some more mixing techniques for vocal tracks.

Depth Processing with Delay
Last month we talked about how depth processing (reverb and delay) utilizes sound reflections and repeats to add spaciousness to vocal tracks. Reverb and delay trick our minds into thinking that the vocals are coming from a larger and 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.

Reverb, echo, and chorus effects all revolve around delay. Echo, slapback delay, and doubling are the simplest forms of delay, utilizing a single repeat or several repeats of an audio signal. Chorus (and its brothers, the phase shifter and flanger) consists of short delays slightly varied in time using modulation. Reverb is a complex combination of blended delays that simulate an acoustical environment, like a sports arena or jazz club.

Echo, Slapback Delay, and Doubling
Basically, delay plug-ins and effects units record a signal, then play it back at a user-selected time delay called "delay time"or "delay length."A single delay of less than 35 ms is called a double, because this effect makes the track sound like there are two tracks of the same part being played/sung at the same time. A slapback delay is a single repeat with a delay time over 35 ms. Slapback delay times of 35 to 75 ms are good for thickening vocal tracks, while delays of 125 to 350 ms are useful for making a vocal track sound large.

It is usually a good idea to set the slapback delay time in relation to the beat and tempo of the song (for example, eighth-note, eighth-note triplet, sixteenth-note, etc.). The rhythm you create with the delay can add a nice groove element. To determine a delay time for your song based on a quarter note beat, use the following equation:

60,000 ÷ song tempo (in beats per minute) = D (delay time per quarter note in milliseconds)

For example, say the tempo of your song is 120 BPM. Well, 60,000 ÷ 120 = 500 ms. So if you want a sixteenth-note delay on the beat, divide 500 ms by four (because there are four sixteenth notes in a quarter note) and you'll have a 125 ms delay.

Adding "feedback"to a slapback delay can smooth out the sound of a vocal track. How? The feedback control sends the delayed signal back into the delay input, creating a delay of the delayed signal. The higher the feedback level, the more delays are created.

Figure 1. Increasing the feedback parameter can smooth out the sound of a delay by simply adding more copies of the delayed vocal signal in with the dry vocal track. Click to enlarge

Chorus, Phase Shifter, and Flanger
Adding modulation to a delay creates slight pitch variations in the delayed signal. Modulation, the varying of delay time, is created using an LFO (low frequency oscillator) and is essential for creating chorus, phase shifter, and flange effects. The LFO speeds up or slows down to alter the playback of the delayed signal, making its pitch rise and fall. These slight variations can actually smooth out pitch problems on a vocal track.

Modulation makes use of acoustical phasing. As you may know, total phase cancellation occurs when two entirely out-of-phase waveforms are combined: they cancel each other out to complete silence. Likewise, combining two in-phase waveforms creates a new waveform with twice the amplitude of the original two waveforms; they add together. It follows that when two waveforms are only slightly out-of-phase with each other, so there's some minor cancellation, they partially reduce the amplitudes of varying frequencies, while slightly additive out-of-phase waveforms partially increase the amplitudes of varying frequencies.

When delayed and slightly pitch-shifted (modulated) signals are combined with each other and the source sound, a constantly changing phase relationship is created between the waveforms. They sum and cancel at varying frequencies. The interaction between the source sound and the modulated delay produces a sound similar to that of several different singers or instrumentalists performing together, and this effect is appropriately called chorus. Modulation depth and rate parameters alter the sound of the chorus effect by controlling the amount and speed of the pitch changes. Chorus effects usually have delay times of 20 to 35 ms.

Depth and rate parameters react differently to delay times. If you set the delay time to around 1 ms to 3 ms you can create a phase shifter effect by creating waveforms that move subtly in and out of phase. This effect sounds like a mid- and high-frequency EQ sweep, and creates an illusion of swooshing motion. Flanging is similar to phase shifting, except that it's more dramatic. The delay time for a flange effect is around 10 to 20 ms, and the rate and depth settings can vary according to your taste. Both phase shifters and flangers are useful on guitars, keyboards, and at times drums, bass, and vocals. I urge you to play with the parameters of the delay effects just to hear the wacky sounds you can make!

	Figure 3. With Waves SuperTap delay, it's easy to assign delay times and panning of the original and delayed signals. Click to enlarge

You can apply the same technique for chorus, phase shift, and flange. Also, try EQing the delayed signals differently than the source to add more frequency separation, stereo imaging, and character to your mix.

Using Delay to Double
One of the simplest things you can do to fatten a track is to double it, either by recording another track of the same part or by electronically doubling the original track. Pan one track to the left and the other to the right, and you've instantly increased the apparent size of the track.

Double-tracking (two distinct tracks): Having two similar recordings of the same lead or harmony vocal part panned out sounds cool; it's the slight differences between the two performances that make this technique sound so good.

One track, electronically doubled: For a tighter (i.e., totally rhythmically-aligned) sound, use a delayed copy of the original track as the panned "double"track. On your mono track, set up a mono send (with a mono bus) to a new mono aux track. Make sure to select "pre-fader"on the send, so the volume fader on the original track doesn't affect the send level. Set the input of the new aux track to the same mono bus as the send output. Pan the audio track to the left and the aux track to the right. At this point, it won't sound any fatter. Why? Because the audio track and the aux track are playing back at almost the exact same time, yielding essentially a mono signal.

To fatten the sound, add a short delay to the Aux track and set the delay length to around 16 milliseconds. 16 ms is a good number because it's enough time to separate the tracks to avoid noticeable phasing, but not really enough time for our ears to separate the rhythmic timing differences between the two tracks. This is a great technique to use when adding other effects to a vocal track, like distortion, AM radio EQ, etc. at certain times in a song.

Adding Special Effects
One of the coolest ways to make your recordings sound unique is to add special effects to your lead and harmony vocal tracks. Some ideas:

Figure 4. McDSP's Chrome Tone plug-in offers up amazing distortion, compression, chorus, flange, EQ, wah, tremolo, spring reverb, and tape delay effects. Click to enlarge

Distortion: Adding distortion can add a distinct energy to a vocal track. When using distortion, I usually double the lead vocal track and add the distortion on the doubled track. That way I have control over both the dry signal and the distorted signal, and can mix in the different sounds at whatever levels I like. Consider using IK Multimedia's AmpliTube, Line 6's Amp Farm, McDSP's Chrome Tone, or Bomb Factory's SansAmp for some cool distortion sounds, or simply for adding a tube preamp sound.

EQ: EQing a vocal track in different ways can create nice ear candy too. EQ a few words differently here and there in a mix to add some dimension to the vocal track. If done subtly, the listener may not hear the change, they'll just feel it… especially if the EQ treatment is added to a particularly meaningful word or phrase in a song.

Delay/Reverb: Similarly, adding more noticeable delay or reverb on specific words or phrases (for example, by unmuting a delay effects loop) can also add some dimension and interest to a vocal track. This technique can actually add meaning to the lyrics by ingraining a certain word in the listener's ear or creating a dreamy state of mind for a brief moment in the song.

Listen to the following MP3s to hear examples of several of these techniques. The first MP3 is part of a song with all the instruments in the mix. The second MP3 has all the vocal parts with their effects soloed. Check out the different layers of sounds, delays, reverbs, EQs, and distortions that are mixed in with the lead and harmony vocal tracks.

MP3 #1: Rock vocals with music

MP3 #2: Rock vocals soloed

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.

Click here to read previous columns.