Singing competition shows have been criticized for their use of sound editing and auto-tune for as long as they’ve been on the air. Though it isn’t made public, it is an issue that producers have had to deal with since these shows started. This came back into light last week when YouTuber and vocal coach Tristan Paredes posted a video about it. Jan 14, 2019  Darci Lynne performs with her puppet pal Oscar on the 2017 season of 'America's Got Talent.' Photo by Trae Patton, NBC. Oklahoma City singer/ventriloquist and 2017 'America's Got Talent' winner Darci Lynne Farmer will compete on the new episode of the new series 'America's Got Talent: The Champions,' airing from 7 to 9 tonight on NBC.

With the return of The X Factor to TV screens, we look at the physics behind pitch correction.

Back on the TV schedule for the autumn, the singing competition programme The X Factor was criticised last year after it emerged that the contestants’ voices were being altered via Auto-Tune.

Producer Simon Cowell subsequently banned any further use of the technology on the show.

But how does audio signal processing help to make singers’ voices sound better?

What would you do if I sang out of tune?

Few singers are perfect. Sometimes, the pitch of their vocal slightly misses the exact note they’re trying to hit.

If they are a little out of tune, the vocal track can still be rescued – or ruined, depending on your point of view – with a little help from the science of signal processing.

The pitch of a note is dependent on the frequency of the sound wave produced – the A above middle C is usually defined as 440 Hz. Therefore manipulating the frequency can produce a different note, or hit an exact note from a noise that is slightly off-key.

Musical scales are divided into 12 pitches each separated by a semitone – the difference in note between two adjacent keys on a piano or frets on a guitar neck. The goal of pitch correction is to retune a slightly high or low note to the nearest semitone.

In the system usually used by MIDI instruments in which pitch is assigned a number, with the 440-Hz A being 69 and each semitone increasing or decreasing the pitch number by 1, it is related to frequency f by a simple formula.

If an attempt at singing that A note actually came out at, say, 445 Hz instead, then using a computer to correct the frequency back down would ensure that the recording sounds in tune.

Sound engineers can’t simply change the frequency by itself, however.

Because the frequency of a wave is related to its speed via its wavelength, the duration of the sound would change too – this is why sped-up tapes sound chipmunk-like.

The frequency can be altered without changing the speed by going digital.

Music by numbers

Although it is possible to alter analogue signals – those based directly on the electrical signal generated by a microphone, or by a guitar pickup – a wider range of effects is possible when working with digital signals.

A digital signal uses discrete values rather than continuous ones, so converting an analogue signal requires taking sets of discrete points or samples. (Higher sampling rates more closely approximate the original sound).

These digital signals can be altered so that a sound produces the correct musical note by using a phase vocoder.

This works by first changing the duration of the sound without altering its frequency, and then changing the frequency to both hit the correct pitch and restore the original duration.

The name comes from its use of the signal’s phase information to manipulate the signal in the desired way.

It breaks an audio signal down into many small, overlapping frames and then changes the spacing of those frames to change the total duration of the sound. In practice, this is a complicated task that requires the use of the advanced maths of Fourier transforms to convert the signal into a form that can be manipulated in this way.

The sound is then resampled to take it back to its original duration and hit the desired note.

As guitarpitchshifter.com explains, if the aim was to double the frequency then this would be as easy as picking one out of every two samples and constructing a waveform from those. But to fit the signal back into its original length when not scaling by an integer, interpolation is used to determine which bits of the sample should go at which points.

For imperfect singers to remain perfectly in key, we have this piece of maths and physics to thank – or to blame.

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Auto-Tune Mobile brings vocal pitch correction to vocal performance, using Antares' world-class Auto-Tune®technology. Now Antares' professional pitch correction recording studio technology is available for local performers touse live, on stage, or in recording apps on your iPhone / iPad.

The Auto-Tune Mobile app does not do anything until you sing through it. When you sing, Auto-Tune Mobile detects whatnote you are singing, and corrects the pitch of your notes, to the nearest valid note, from the ones you select on thescreen. The corrected vocals go out through the speakers (when you turn on Audio Out); also Auto-Tune Mobile iscompatible with other apps if you wish to record.

Connect Auto-Tune Mobile to your sound system between your microphone and your P.A. / speakers to use Auto-TuneMobile in a live performance setting. Use a microphone audio interface device to connect the 1/8 inch jack to yourmicrophone line and the headphone output to your sound system. Turn on Audio Out on the Auto-Tune Mobile app to getaudio to pass through the system. If you turn on Audio Out without connecting to your sound system, you are likely tohear the internal feedback of the internal speaker to the internal mic. Adjust your mic and speakers so there is nofeedback.

Vocals are corrected to the nearest pitch based on the key and scale of the song, or to a set of melody notesselected on the screen. Use the Chromatic scale when you don't know what key or scale a song is in. This is theeasiest way to correct your voice to the nearest pitch.

The Retune speed is the time it takes for Auto-Tune to pitch correct your voice. The Normal Retune speed is a settingof 50 msecs -- this gives a natural humanized pitch correction effect. Normal Retune speed is appropriate for a moderatetempo song, for example a song at 120 bpm with a melody in eighth notes.

A funky or fast tempo tune, or a song requiring sixteenth note precision, will likely require a Fast Retune speed.The Fast Retune speed corrects notes within 25 msecs; this is better for faster notes. For slow songs or balladsfeaturing long held notes, the Slow Retune speed (75 msecs) may provide a more natural sound.

In addition to natural sounding pitch correction, you can also apply the iconic Auto-Tune effect. The Auto-Tuneeffect in essence retunes your pitch immediately (in 0 msecs). Ironically, if you sing really well, there is not muchcorrection for Auto-Tune to do. The Auto-Tune effect is most noticeable when you are off key or you slide into a note.Also when you set the app to the Auto-Tune Effect setting, a meter appears at the top (red bouncing ball) that visuallyindicates whether you are singing sharp or flat.

The Bypass button is provided as a quick way to stop and start adding the effect as you sing.

Auto Tune Darcy Agt 2016

Auto-Tune Mobile conforms to the Inter-App Audio (IAA) standard so you can use Auto-Tune with your other IAA apps. Notice when using with GarageBand that the Auto-Tune filter takes effect as you record the track. If you want to pitchcorrect a pre-existing vocal you will need to replay it outside of GarageBand and re-record it to a new track. Midicontrol of pitch correction is included, so you can connect a Midi keyboard and direct the vocals to sing on aparticular melody or on a set of scale notes as pressed on the keyboard. Midi note presses will show up in red on theapp.

Auto-Tune Mobile is Audiobus compatible, allowing Auto-Tune Mobile to work with your other iOS music apps. Auto-TuneMobile acts as a filter in the “Effects” category, so you can apply pitch correction and the Auto-Tune effect to otherAudiobus-compatible apps. (see http://audiob.us).

Auto Tune Darcy Agt Results

* Vocal real-time pitch correction designed for live performance
* Compatible with other IAA and Audiobusapps
* Built with Antares Audio Technologies' Auto-Tune® professional pitch correction
* Tested with TascamiXZ and IK Multimedia's iRig microphone audio interfaces.
* Made for musicians.