Antares AutoTune user manual

							 
Auto-Tune UserÕs Manual
 
11
 
CHAPTER 2
 
Introducing Auto-Tune
 
Auto-Tune is a breakthrough in digital signal processing (DSP) in the music
industry. It puts you in control of pitch. Moreover, Auto-Tune is a precision
instrument for controlling pitch, allowing you to apply nuances of intona-
tion to any performance. These nuances were only previously available to
synthesized music if the engineer involved was willing to do a lot of work.
Access to this new level of control is achieved by any Auto-Tune user who
has a basic understanding of pitch and how Auto-Tune functions to correct
for pitch errors. This chapter presents basic terminology and introduces
Auto-TuneÕs operating paradigm, giving you information you need to use it
effectively.
 
What Is Pitch? 
Pitch is a quality of sound relating to the frequencies of the energy involved.
Some sounds are very complex and donÕt involve energy of speciÞc fre-
quencies. Even then, there is pitch. Compare, for example the pitch of hiss-
ing steam with the rumble of an earthquake. Other sounds, although still
complex, have more speciÞc pitch. A symphony orchestra playing a scale in
unison is an example of this. The waveforms involved are very complex;
nonetheless, you are able to easily sense the pitch.
Vocalist and the majority of individual instruments have the most clearly
deÞned quality of pitch. The sound-generating mechanism of these sources
is a vibrating element (vocal chords, a string, an air column, etc.). The sound
that is generated consists of energy at a frequency (called the fundamental)
and energy at frequencies that are integer multiples of the fundamental fre-
quency (called harmonics). These sounds have a waveform (pressure as a 
						

							 
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Auto-Tune UserÕs Manual
 
function of time) that is periodic. This means that the waveform repeats
itself, such as the periodic waveform shown in the diagram, below.
Other sounds are more complex. The non-periodic waveform, above, is
from a violin section playing a single tone. Our ears still sense a pitch, but
the waveform does not repeat itself
This non-periodic violin section is a summation of a number of individually
periodic violins. The summation is non-periodic because the individual vio-
lins are slightly out of tune with respect to one another.
 
Some Terminology 
The pitch of periodic waveforms is deÞned as the number of cycles per sec-
ond of the waveform. This unit is named Hertz (abbreviated Hz.). The stan-
dard instrumental tuning is A3 = 440 Hz. 
Pitches are often described relative to one another as intervals, or ratios of
frequency. For example, two pitches are said to be one octave apart if their
frequencies differ by a factor of two. Pitches which are integer multiples of
one-another sound more ÒharmoniousÓ when played together, whereas
pitches that are not are said to be ÒdissonantÓ.
Pitch ratios are measured in units called ÒcentsÓ. There are 1200 cents per
octave. For example, two tones that are 2400 cents apart are two octaves
apart and have a pitch ratio of 4 (or 1/4). 
Periodic Waveform:
Digiwave
Non-periodic Waveform:
Violin Section 
						

							 
Auto-Tune UserÕs Manual
 
13
 
The Purpose of Pitch Correction
 
The twelve-tone Equal Tempered Scale consists of tones that are, by deÞni-
tion, 100 cents apart. These are called semi-tones. This scale is the ubiqui-
tous scale used (or rather approximated) in 99.9% of all Western tonal
music. The twelve equally-spaced tones of the Equal Tempered Scale hap-
pen to contain a number of intervals that approximate integer ratios in
pitch. The following table shows these approximations: 
As you can see, the intervals in the Equal Tempered Scale are NOT equal to
the harmonious integer ratios. Rather, the Equal Tempered Scale is a com-
promise. It became widely used because once a harpsichord or piano is
tuned to that scale, any composition in any key could be played and no one
chord would sound better or worse than that same chord in another key. In
modern times, synthesizers can generate any intonation at any moment,
allowing the use of ideal pitch ratios when ever they are desired.
 
The Purpose of Pitch Correction 
When voices or instruments are out of tune, the emotional qualities of the
performance are lost. Correcting intonation solves this problem and
 
Interval CentsNearby 
RatioRatio 
Cents
 
minor second 100 16/15 111.73
major second 200 9/8 203.91
minor third 300 6/5 315.64
major third 400 5/4 386.31
perfect fourth 500 4/3 498.04
tritone 600
perfect Þfth 700 3/2 701.95
minor sixth 800 8/5 813.69
major sixth 900 5/3 884.36
minor seventh 1000 16/9 996.09
major seventh 1100 15/8 1088.27
octave 1200 2 1200
 
TABLE 1. 
 
The Equal Tempered Scale 
						

							 
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Auto-Tune UserÕs Manual
 
restores the performance. Auto-Tune is mostly used to solve these gross
intonation problems. However, as you shall see, Auto-Tune is also a preci-
sion instrument, allowing intonation to be controlled to extraordinary
degrees of accuracy. This allows the tonal aspects of music to be controlled
accurately and easily to achieve any desired consonance or dissonance in
harmonies.
Dont try to raise the pitch more than an octave. Auto-Tune has a built-in
limitation of not being able to raise a pitch more that one octave (1200
cents). This is not considered a problem since most pitch corrections will be
+/- 20 cents.
 
How Auto-Tune Detects Pitch 
In order for Auto-Tune to automatically correct pitch, it must also detect the
pitch of the input sound. ItÕs easy for you to calculate the pitch of a periodic
waveform: Simply measure the time between repetitions of the waveform.
Divide this time into one, and you have the frequency in Hertz.
Auto-Tune does the same thing: It looks for a periodically repeating wave-
form and calculates the time interval between repetitions.
The pitch detection algorithm in Auto-Tune is virtually instantaneous. Like
your eye-ball, it can see the repetition in a periodic sound within a few
cycles. This usually occurs before the sound has sufÞcient amplitude to be
heard. Used in combination with a slight delay (about 1 to 10 milliseconds),
the output pitch can be detected and corrected without artifacts in a seam-
less and continuous fashion.
Auto-T
une will not detect pitch when the input waveform is not periodic.
Hence, Auto-Tune will fail to tune up a violin section. (It is possible to tune
up an out of tune violin section, either tuning the sound as is, or by tuning
up the individual players within the sound. This is done on samples for
synthesizers using the Antares Audio Technologies InÞnity software. Using
InÞnity, you can actually made a community orchestra sound like the New
York Philharmonic. But InÞnity processes samples, whereas Auto-Tune is
used on performances.)
Back to Auto-Tune, if the input waveform is not periodic, Auto-Tune will
fail. At times, this can be a problem. Consider, for example, a breathy voice,
or a voice recorded with a wind sound. The added noise is non-periodic, 
						

							 
Auto-Tune UserÕs Manual
 
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How Auto-Tune Corrects Pitch
 
and Auto-Tune will have difÞculty determining the pitch of this sound.
There is a slider (the Tracking slider, discussed in Chapter 4) that will allow
Auto-Tune to be more casual about what it calls ÒperiodicÓ, which will help
in these cases.
If you have problems processing a particular sound, zoom it up and look at
it. If it is non-periodic, Auto-Tune will not work. If you can correct that
problem, by using EQ or re-recording, then those are options available to
you.
The precision by which Auto-Tune detects pitch is extraordinary. At a fre-
quency of 400 Hz and a sample rate of 44100, the Auto-Tune DSP algorithm
computes the pitch to an accuracy of .0001 samples per cycle, or .0004 Hz.
At this resolution, the very question ÒWhat is pitch?Ó becomes relevant.
That is, as the pitch of typical performances continuously change, the
amount of variation in pitch, even over the time of a few cycles, changes
greatly in comparison to the accuracy by which Auto-Tune computes pitch.
The pitch computed by Auto-Tune is a mathematical estimate of the cycle
period repetition rate over the last two (or sometimes the last four) cycles.
Auto-Tune was designed to detect and correct pitches up to C6. In reality, if
a pitch goes higher than C6, Auto-Tune will often interpret the pitch an
octave lower. This is because it interprets a two cycle repetition as a one
cycle repetition. These pitches can be corrected by the usual means. On the
low end, Auto-Tune will detect pitches as low as A0 (55Hz). This range of
pitches allows intonation correction to be performed on all vocals and
almost all instruments.
 
How Auto-Tune Corrects Pitch 
Auto-Tune changes the instantaneous pitch and introduces no distortion in
the output. It does this using the same basic computations used in samplers
to re-tuned samples.
This is different from other pitch-shifting algorithms which put noise in
sounds as a result of FFT (Fast Fourier Transform) overlap-and-save algo-
rithm phase errors. The Auto-Tune algorithm is very clean and transparent.
It isnÕt possible to tell that a sound has been processed by Auto-Tune -
except that it is in-tune. 
						

							 
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Auto-Tune UserÕs Manual
 
The accuracy of pitch correction in Auto-Tune is exceptional. In the worst
case, a continuously varying tone can be corrected (at the discretion of the
user) to within an error of at most one cycle in 80 seconds (assuming the
Retune slider is set to zero). These accuracies are equivalent to the .01 cent
accuracies by which the various scales of the Automatic Mode (discussed
below) are internally speciÞed. These accuracies are also equivalent to the
accuracies of the clocks which control music studio functions.
Chapter three will step you through a demonstration where two badly out
of tune C2Õs are independently tuned to the same standard with no beat
cycles. (Beat cycles are the perceptual result of hearing two tones that are
close in frequency. As the relative phase of the fundamental and harmonics
change from in phase to out of phase, constructive and destructive rein-
forcement occurs which alternately makes the composite sound loud and
soft.)
 
Auto-Tune Modes: Automatic and  
Graphical 
Auto-Tune has two separate and distinct ways to operate, almost as if there
were actually two separate programs in one package. These are called
modes, and are named the Automatic Mode and the Graphical Mode. The
Automatic Mode and Graphical Mode function separately; when one is
active, pitch corrections of the other are not performed.
Both the Automatic and Graphical Mode allow the ÒbypassÓ button to be
used. Even though bypass is a well known plug-in control, I mention it
because it functions seamlessly and can be used to punch pitch correction
on and off during processing.
 
The Automatic Mode 
The Automatic Mode works by continuously tracking the pitch of the input
sound and comparing it to a scale. The scale tone having pitch closest to the
input is continuously identiÞed. An output pitch is generated which is
closer to the scale tone than the input pitch. You have control of the scale. 
						

							 
Auto-Tune UserÕs Manual
 
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The Automatic Mode
 
Major, minor, chromatic and 26 historical, ethnic and microtonal scales pro-
vide unprecedented control of the output tonality. Scale pitches can be dis-
abled causing no pitch correction. Scale pitches can also be removed
allowing a wider range of pitch correction for neighboring pitches. The
scale can be de-tuned, allowing pitch correction to any pitch center. You
also choose the key of the scale.
You have control over how rapidly, in time, the pitch adjustment to the
scale tone is made. This is done with the Retune slider (fast to slow set-
tings). Fast Retune settings are more appropriate for short duration tones
and for mechanical instruments, like an oboe or clarinet. A fast setting will
remove a vibrato. Slow Retune settings are appropriate for longer tones
where you want expressive pitch gestures (like vibrato) to come through to
the output. A slower setting can leave a vibrato unmodiÞed but accurately
adjust the pitch center to be in-tune.
The Automatic Mode can also introduce a vibrato into the sound. The
Vibrato Section lets you control the depth, rate and delay of the vibrato. You
can also choose the style of pitch variation in the vibrato (sine, ramp or 
						

							 
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Auto-Tune UserÕs Manual
 
square).You would use the Vibrato Section when you have a vocalist who
has not learned to use his (or her) own vibrato. It can also be used for spe-
cial sound design effects.
A fast pitch adjustment to remove an existing vibrato can be used in con-
junction with the Vibrato Section to replace a vibrato with a new one. This
will not always give good results, though, (as discussed in Chapter 3),
because there are usually accompanying changes in the loudness of the
sound.
 
The Graphical Mode 
The Graphical Mode is similar to the Automatic Mode in that it also contin-
uously tracks the pitch of the incoming sound and modiÞes the output pitch
to be closer to a desired pitch. But in the Graphical Mode, the desired pitch
is not a scale tone, rather it is given graphically by you and is called the Òtar- 
						

							 
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The Graphical Mode
 
get pitch functionÓ. As in Automatic Mode, the rate of change towards the
desired pitch (the target pitch function) is controlled by the Retune slider.
The Graphical Mode uses the Pitch Graph:
In this graph, higher pitches are upwards and increasing time is to the right.
The lighter (red) curve is the input sound pitch and the darker line is a tar-
get pitch function. The light, horizontal lines are scale pitches. The key
annotation, scale names, scale pitches and Detune value are those deÞned
in the Automatic Mode. They do not affect the computations of the Auto-
matic Mode in any way. They are merely annotated on the Pitch Graph to
guide you in setting the target pitch function. To change them, choose the
Automatic Mode and change the Key popup, Scale popup, or the Detune
slider, respectively. Moving the detune slider down (more negative) causes
the horizontal line to go down (ßatter).
The Graphical Mode also uses the Envelope Graph:
This graph shows the envelope of the sound whose pitch is shown in the
Pitch Graph. The horizontal scale of this graph will either 1) show the entire
envelope of the pitch-detected sound or 2) align the envelope to the hori-
zontal scale and position of the Pitch Graph. 
						

							 
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Auto-Tune UserÕs Manual
 
In Graphical Mode, the user draws the target pitch function using line and
curve drawing tools. Complete image sizing and scrolling controls are pro-
vided. A graphical editor allows easy editing, including cut, copy and paste
functions. 
The basic steps you will perform in Graphical Mode are:
 
¥
 
Select some sound for processing. This is done in the Soundbites win-
dow.
 
¥
 
Bring up Auto-Tune. Set the buffer for a few seconds longer than the
duration of the audio you are going to tune. Press the Track Pitch button,
then play back the sound. The pitch will be detected and then displayed
in the Pitch Graph as a red curve.
 
¥
 
Create a target pitch function using the graphical tools and adjust the
Retune slider for the desired effect.
 
¥
 
Press Correct Pitch and play back the sound. This will cause the pitch to
be corrected as speciÞed.
In Graphical Mode, Auto-Tune sometimes identiÞes the pitch to be an
octave lower than it really is. In these cases, simply correct the pitch as you
would if the pitch was lower (ex. +/- 20 cents). Auto-Tune will apply this
correction to achieve the desired result.
In Graphical Mode, it is important that the sound played back for pitch correc-
tion begins precisely at the same spot as the sound played back for pitch detec-
tion. This is because the plug-ins do not know the absolute Òtime-of-dayÓ. The
speciÞed target pitch will be applied to whatever sound occurs after playback
begins, even if it is a completely different sound.
In other words, before you press Correct Pitch and play, make sure that the
counter is set to start from the exact place you started Track Pitch.