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How do Autotune Microphones Work

How do Autotune Microphones Work

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Although you might think you’ve heard of the autotune microphone, you’re probably a little mystified as to how it actually works!

Read on all will become clear.

If you’re a keen singer and like to perform live or record your own songs or covers, autotune will help you no end to hit the perfet note. However, the secret as to how this works doesn’t lie in the microphone itself but the software behind it!

Starting with a digital sound

So just how does the technology work to adjust a singer’s voice to sing in key? In a nutshell, you sing into a digital microphone and a piece of kit called a vocal effects processor runs behind the scenes to correct your pitch. This autotune effect is then applied to your notes/song.

The clever autotune software monitors your singing and notes during your performance, correcting you where necessary. The end result is that you sound fabulous, whether you can actually sing in tune or not!

A highly sophisticated algorithm

The true secret to autotune is a very sophisticated algorithm that processes

digital signals on a digital audio interface like a mixing desk, PC or a Mac. The route the sound takes runs from your microphone to the sound interface. Autotune is then applied using downstream electronics and software. The person controlling the autotune software will need to tell it what key the song is in before you start to sing.

This enables to software to set the correct parameters, which it will then work within. If you sing a bum note, the software is able to work out what note you meant to sing. It will adjust the note accordingly by nudging it up or down into the right position.

Singer with a mic

Let’s get technical

To get a better understanding of autotune, you need to understand a little about how notes are produced.

Stay with me.

A note’s pitch comes from the frequency of the corresponding sound wave to that note. For example, the note A above middle C (which orchestras typically tune up to) is at a frequency of 440 Hz. By changing the frequency, you can change the note. This works for notes that are slightly off their intended frequency, i.e., a little off-key.

Autotune will tune any given note within its parameters to the nearest semitone note within the scale. There are 12 semitones in every scale and the software picks out what semitone note it thinks you’re trying to hit and adjusts the frequency accordingly.

With digital sound signals, notes are assigned numbers. So the A above middle C is 440 Hz or number 69. Every semitone change up or down adds or removes 1 from this number. If you tried to hit that ‘A’ note above middle C and you actually sang a note at 445 Hz instead of 440 Hz, the software would change the frequency to the correct level for you. Therefore, autotune ensures you stay in tune.

Singing with auto tune mic

Introducing the phase vocoder

Interestingly, frequencies can only be changed when notes are digital. Trying to change the frequency on an analogue recording would lead to you sounding like a chipmunk!

Digital signals are changed to hit right note via what’s known as a phase vocoder. This takes its name from the way this piece of kit uses phase information from the signal to manipulate it in the desired way. First of all, it changes the sound’s duration. Then, it changes the frequency to get the correct note before matching the original duration.

Getting into the nitty-gritty, the phase vocoder breaks down an audio signal into multiple tiny overlapping frames. Next, it alters the spacing between these frames so that the overall duration of the note is changed.

The algorithm that does this is extremely sophisticated and uses advanced mathematics. The formula changes the signal into a form that can then be manipulated.

Finally, the sound is resampled and is put back to its original duration – while actually hitting the correct note this time around!

Going for a natural or more processed sound using autotune?

The autotune process can be calibrated by the user. For example, you can go for a natural sound where your voice is guided smoothly back to the correct pitch. Alternatively, you can use the software to create an artificial sound, which is still very appealing.

In fact, this has become all the rage in genres like hip-hop and pop. Think back to Cher’s chart-topping 1998 hit ‘Believe’ and you’ve got the perfect example of autotune creating a great processed sound. Not all microphones have the auto tune feature particularly clip on microphones as these are designed more for commentry and not for singing.

The surprising origins or autotune

Auto-Tune’s invention originated from an entirely unconnected area – searching for underground oil through sound waves! A geophysicist invented a system called ‘autocorrelation’, which he used to interpret sound waves. Then, when the 90’s dawned, this technology was applied to vocals.

Recording studios and sound engineers became very excited about it and rightly so. Today, autotune helps billions of singers from amateurs to professionals to sound in tune, with better performances and more pleasurable listening for all kinds of musical genres.

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