Paul White studio‑tests the sound engineer's dream — a TDM software plug‑in for undetectably correcting vocal and monophonic instrument pitching problems.
Every studio owner will be familiar with the problem of the young band who come in to record a track, but then find that while their singer is full of passion, the pitching is at best dubious, and certainly not up to professional standards. Perhaps you have the patience to cajole the singer into trying again with more emphasis on pitch accuracy, but then you find the fire has gone out of the performance. Even pros suffer from this problem to some extent; somebody who goes down a storm on stage may well be less impressive when they have no visuals and atmosphere to support them. What's needed is a magic potion that will help singers stay in tune, without losing their expression or energy. To my knowledge, no such thing exists, but Antares Systems' Auto‑Tune software comes a pretty close second.
Auto‑Tune is a software plug‑in pitch processor capable of tracking the pitch of virtually any monophonic performance, then correcting it by one of two means. In automatic mode, the performance is shifted to bring it in tune with any desired scale entered by the user, but unlike rigid pitch‑shifting devices, Auto‑Tune enables the operator to determine the degree of correction, and also the rate of correction, so that natural scoops, swoops and vibrato can be retained if desired. What's more, if the singer has problems only with certain notes, individual notes can be bypassed on the target scale, so that pitch correction is applied only to specific notes. For more surgical precision on individual words or phrases, Auto‑Tune has a graphical mode, where the pitch of the original performance can be viewed on a time/musical pitch grid. Various tools, similar to those found in basic computer drawing packages, are provided to enable the operator to create or modify the target graphical curve. The section can then be processed to conform to the new pitch graph. The most important thing to remember in Graphical mode is that the section of sound analysed must remain in the same position for processing. If you move it, Auto‑Tune will carry out the correct operations, but in the wrong place. This is a 'feature' of the TDM plug‑in system and not a fault of the program.
Auto‑Tune's claim to fame is the extremely high quality of its pitch‑shifting. The process is different to that used in regular pitch‑shifters, and avoids all the unnatural warbling and glitching you often find in budget hardware pitch‑shifters. In fact, the only real limitation is that the program can't track chords or ensemble instruments — clean tracking can only be achieved on solo, monophonic instruments and voices, and even then some sounds that contain a lot of unpitched sound can fool it. For conventional voices or instruments, though, it performs surprisingly well.
In automatic mode, a conventionally styled plug‑in window appears with just six on‑screen sliders and a few parameter windows. The Scale window is used to select the scale type, which can be anything from an obscure ethnic scale to a simple chromatic type, and below this is the Key window. You may edit the scale if the types on offer aren't suitable for your needs.
The sliders are separated into two groups, one for pitch correction and one for adding delay vibrato to the result. Detune provides an offset for working on material that isn't in concert pitch, while Retune controls the rate at which the sound being processed is pulled towards the target pitch. If this is set too fast, the process will start to strip out the human features of performance, such as slides up to notes, or vibrato, whereas if it is too slow, the note will be corrected too late. Tracking strength is controlled by the Tracking fader, where a maximum setting gives the tightest tracking, and the minimum setting applies little correction. This is useful, as forcing every note to perfect pitch may sound a little artificial. A readout in the centre of the window shows the percentage pitch change being applied. Most of the time this should only be a few tens of cents, but the system has a maximum range of plus or minus one octave.
Now there really is a way to fix dubious vocals.
The vibrato section enables vibrato to be added to performances, and there's a range of modulating waveforms here as well as full control over depth, rate and delay. In theory, you could even strip out a performer's natural vibrato and then add your own, but this might sound unnatural in some cases, as the performer's own vibrato will probably be accompanied by level and timbral changes.
Graphical mode is best for correcting short sections of music where either the rate or extent of a pitch slide is wrong, or where the pitching is so far out that the automatic mode might push it a complete semitone out of tune. The process is fairly simple, and involves first playing the offending part while Auto‑Tune analyses it. The resulting graph of pitch against time is plotted on a musical grid corresponding to the notes of the scale selected in Automatic mode, and after just a little practice you can see which notes are likely to sound out of tune. After analysis, the computer creates a black curve to match the red one on screen, and this may be edited using simple dragging, straight line or jointed straight line tools. Nobody sings bang on pitch, but the note should waver around the right note more or less symmetrically. If it doesn't, you can either move the whole section of curve up or down, drag just one end of the curve (great for correcting dropping or rising pitches), or replace part of the curve with your own collection of straight lines.
Another useful inclusion in the graphical mode is a facility to create the pitch correction that would have occurred in Automatic mode. With care, Graphical mode offers almost unlimited scope for pitch correction — it's all down to how much time (and patience) you have.
I used Auto‑Tune with my Pro Tools III system, and as you might expect, the fully Automatic mode of operation is the easiest to use. Indeed, if a performance is more or less OK, it may well be all you need to bring it bang into pitch. Even so, some user skill is involved, because if you make the pitch tracking too tight the voice seems to yodel from one pitch to another in a most unconvincing manner. Of course, if you're in the business of creating ethnic‑sounding vocal samples, this can be a useful effect. Careful adjustment to reduce the speed of tracking and the degree of correction results in a very natural sound that is gently nudged towards the target pitch — it only falls over when the vocalist is so far out that the next note in the scale is closer than the desired note. Once you have the best settings, just play through the file and bounce it to a new track to make it permanent.
After playing with the system for a while, I've come to the conclusion that while the graphic mode might be a lot more time‑consuming, you can achieve excellent results if you've the patience. With a little practice you can get quite quick at it, but there is one snag, which is largely down to the way in which Pro Tools handles plug‑ins. You can't create a set of 'fix' parameters for a section of audio and then process it as you can in Sound Designer — you have to change the buss routing, bounce the section down to a spare track, slide the new section over the original, switch the monitoring back to the way it was, then move onto the next phrase that needs sorting. That's the only way I could find of making the change permanent, and you have to finish working on one section before you can go onto another, otherwise your work is lost. Trying to process too long a section of audio at once means setting up a longer buffer time than the default 10 seconds, and if it's too long, everything slows right down (30 seconds seems about the upper limit on my computer before things get annoyingly slow). What's more, you have to take care not to de‑select the section of audio you're working on until the bounced track has been created, otherwise the pitch correction information won't be in sync with the audio — another legacy of Pro Tools. Ultimately, of course, you have to live within the confines of Pro Tools, and, in fact, restricting the sections of audio you process to 30 seconds doesn't present too much of a problem.
So what about the sound quality? Providing you're trying to correct a vocal that is reasonably well sung in the first place, the results sound perfectly unprocessed. On a test piece involving a ballad with one note well over a semitone off pitch, it was possible to end up with a natural‑sounding performance that I would never have guessed had been doctored in any way, although, as usual, excessive or unsympathetic pitch correction will result in 'yodelling'. In all, it took me less than 30 minutes to feel comfortable with the system. The only thing I couldn't do successfully was remove a fast, deep vibrato, because if you set the response too fast you get a trill, and if it's too slow, the vibrato remains. To be fair though, this isn't something you'd want to do often — you're more likely to want to fix basic pitching problems, or perhaps add a little delay vibrato to a flat‑sounding voice.
Auto‑Tune is an exceptional piece of software that makes serious, undetectable turd polishing a reality! Now there really is a way to fix dubious vocals, although admittedly the more dubious they are, the more effort and tenacity it takes to come up with a perfect result. If a vocalist has made a reasonable stab at a track, the Auto mode may be all that's needed, and if there are just one or two very dodgy sections, you can fix those first in the Graphical mode, and then put the complete file through again on auto‑pilot. There are very few things about the program that irritate me, though I found it difficult sometimes to grab just one end of a curve without selecting the whole thing instead, and though I dearly wanted to be able to press a Process button to make my changes permanent in the original file, I realise that Pro Tools III doesn't accommodate that way of working — and I'm not yet sure whether Pro Tools 4 offers a way around this particular problem.
In short, if you have a Pro Tools TDM system and you work with vocals, Auto‑Tune is one product you can't afford to be without.
- Natural‑sounding pitch correction can be carried out with no audible side effects.
- Easy to learn.
- With Pro Tools III, it isn't possible to process sections of a file —
A remarkable tool that can be used both to tighten up the pitching of a performance, or to salvage the occasional serious pitching error.