Adventures in Vocal Processing

Nov 1, 2006 12:00 PM, By Geary Yelton

           

For as long as people have been singing, many have hoped for some miracle that would make them sound like better singers than they really were. Powerful computers and recent advances in audio software have given new life to such hopes by making it possible to correct and enhance vocal tracks that might otherwise be unsalvageable. In a modern studio, software-based tools extend an audio professional's ability to capture less-than-perfect vocal performances and turn them into first-rate recordings that surpass physical reality.

No matter what type of music you record, at one point or another you'll probably want to record the oldest musical instrument in existence, the human voice. The vocal track is usually the most important component of any song that isn't entirely instrumental. Virtually every studio, large or small, processes vocals to enhance their appeal. By adding reverb, compression, and other traditional forms of sweetening, recordists give vocal performances a professional polish that overcomes lackluster sound. Digital recording, however, has given rise to a new generation of tools that go beyond sweetening.

In this article, I'll survey some applications and plug-ins that are best suited for treating vocals, and I'll investigate the types of processing they provide. These products fall into categories that encompass physical modeling, pitch correction and transposition, time expansion and compression, breath and sibilance control, and simulating multiple voices. I've selected eight products (including bundles) from six developers: Antares Auto-Tune 4 and Avox, Cakewalk V-Vocal, Celemony Melodyne Studio 3.1, Synchro Arts VocALign Project 2.9, TC-Helicon Intonator HS and VoiceModeler, and Waves Vocal Bundle.

Melodyne and VocALign Project are standalone applications. Avox and Vocal Bundle are plug-in suites, but most of their plug-ins are also available separately. Auto-Tune, Intonator HS, and VoiceModeler are individual plug-ins, and V-Vocal is a dedicated vocal processor within Sonar 5 and 6 Producer Edition. All except the TC-Helicon plug-ins run native and require no DSP acceleration, and all except V-Vocal are cross-platform and run under both Mac OS X and Windows XP.

Voices in My Head

Complex audio processing consumes lots of CPU cycles and needs plenty of RAM, especially when using multiple plug-ins. I ran everything except V-Vocal on my desktop computer, a dual-processor 2.3 GHz Power Mac G5 with Mac OS X 10.4.7, 4 GB of internal RAM, and a MOTU PCI-424 card connected to a 2408mk3 audio interface. To run V-Vocal in Sonar 5, I recruited my notebook computer, a Dell Latitude D610 with a 2 GHz Pentium M, 1 GB of RAM, and Windows XP Professional, connected to an M-Audio Ozonic by means of a StarTech FireWire card.

For the plug-ins, my host applications were BIAS Peak Pro 5.2, Digidesign Pro Tools M-Powered 7.1, Steinberg Cubase SX 3.1.1, and MOTU Digital Performer 4.61. Because Melodyne Studio 3.1 also hosts AU plug-ins, I occasionally used it for that purpose as well. Additionally, I borrowed a TC Electronic PowerCore FireWire, which was necessary to run the TC-Helicon plug-ins.

For source material in my explorations, I used recordings of my own voice, audio examples included with the software, and vocal tracks taken from studio recordings. Because of copyright issues, however, I was unable to use any of the studio recordings as Web Clips. Consequently, I also recorded and manipulated samples from Zero-G's virtual instrument Vocal Forge, which pairs 1.25 GB of phrases sung by studio singers with Native Instruments Intakt Instrument.

Antares Auto-Tune 4

When the original Auto-Tune was released in 1997, its impact on pop music was almost immediate. Since then, its influence has grown to such an extent that it has become almost ubiquitous in recording studios, on CDs, and on the radio. Quite simply, Auto-Tune processes a monophonic vocal or instrumental performance and automatically corrects any flat or sharp notes. Rather than rerecording a good take plagued by bad notes, you can process it with Auto-Tune and get perfect intonation. The AU-, DirectX-, MAS-, RTAS-, TDM-, and VST-compatible plug-in has been a boon to marginal singers and a tremendous time-saver for recording engineers and producers everywhere.

FIG. 1: Auto-Tune’s Make Auto function gives you the best of both modes, automatically correcting pitch to a predefined scale and displaying a pitch contour that you can edit as needed.

Auto-Tune 4 (Mac/Win; native, $399; TDM, $599) provides two pitch-correction modes, Automatic and Graphical. Automatic mode continuously analyzes an input's pitch and corrects it to match one of 29 preset scales. An onscreen keyboard visually indicates pitches that Auto-Tune detects in real time; you can use the keyboard to select notes to bypass or remove from the scale. In addition, you can use a MIDI instrument to enter scale data or to select notes to be corrected in real time, effectively transposing the source audio to track whatever you play. And although Graphical mode offers numerous parameters for controlling vibrato, Automatic mode's vibrato functions give you greater flexibility.

Graphical mode continuously analyzes an input's pitch too, but rather than correcting it to a predefined scale, it relies on the Pitch Graph display, which plots pitch against time. You begin by clicking on the Track Pitch button and playing the track to detect its pitches. The original pitch contour will display variations in pitch, with grid lines visually referencing fixed pitches. You then create a target pitch contour, either by clicking on the Make Curve button to duplicate the original, by clicking on the Make Auto button to draw a new contour that conforms to the current Automatic mode settings (see Fig. 1), or by drawing new targets from scratch using the curve- and line-drawing tools. You can then edit the target pitch contour using an assortment of cursor tools. Audition the selected audio and click on the Correct Pitch button to finalize your changes.

FIG. 2: Scheduled for imminent release, Auto-Tune 5 will feature an improved detection algorithm, an updated user interface, and several additional enhancements.

Either mode lets you specify the sampling rate, input type (low male voice, for example), Retune Speed, and Tracking. The Retune knob controls how quickly pitch correction will be applied to the input; its highest setting produces instantaneous correction and usually results in characteristic artifacts you've probably heard on the radio (see Web Clip 1). The Tracking knob adjusts Auto-Tune's pitch-detection algorithm to compensate for any noise in the signal; its proper setting depends on whether the vocal track is free of extraneous sounds such as breath or background instruments.

Although Auto-Tune 4 was the current version when I wrote this article, a major update should be available soon (see Fig. 2). Auto-Tune 5 will feature a revised user interface, host transport synchronization, full-time correction mode, a Natural Vibrato function, and a dedicated Snap to Note button. Additional enhancements will include a Humanize function that allows different Retune Speeds for short and sustained notes, and a real-time pitch-tracking display.

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