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Latest Posts » Educational, How To » Vocoders - Synth Keyboards

Vocoders

Written by v on August 13, 2009 – 8:18 pm -

The vocoder is a very polarising device – it drives some people wild, it drives others nuts, but everyone who’s listened to modern music in the last three decades or watched cartoons had heard one. This is the effect used to produce a robotic voice or talking instrument.

Traditionally, vocoders have been dedicated units – boxes, with two audio inputs – a sound source and a microphone. It analyzes the human voice to measure the formant characteristics  and superimposes them over the tonal qualities of the input sound.

It is very similar in effect to the talk box, where a sound source is fed down a pipe into the user’s mouth and the user moves their mouth, jaw and tongue to modify the sound. The vocoder is also commonly confused with autotune – the quite recently developed pitch correction technology that can also be used for artistic effects.

Nowadays, vocoders are often built into synth keyboards like the Korg MS-2000, Radias and Microkorg series. They are also implemented in software in digital audio workstatation packages including Reason and Ableton Live.

In this article, we’ll talk about the history of the vocoder, how it works, its use in popular culture and how you can use one.

History of the Vocoder

The vocoder was originally invented as a military communications device to allow human speech to be transmitted more efficiently over radio.

Everyone has vocal chords which produce a fundamental sound. When you move your jaw, mouth and tongue as you speak, these act like a filter that changes the spectrum of the fundamental sound, to produce recognisable vowels and consonants.

The original vocoder would analyze a human voice and measure the formant qualities at various frequency bands. At the other would apply this information to a synthetic vocal chord sound, creating an approximation of the original speech.

The Vocoder as an Instrument

In the 60’s,  musicians discovered that if  the decoding stage was modified by replacing the synthetic vocal chord sound, with another sound, e.g.  a plucked guitar string, you would still hear an intelligible voice, but with a timbre unlike anything natural. Hence, the association of vocoders with robotic voices.

The German Band Kraftwek pioneered the use of vocoders in popular music, with their popular songs “The Man Machine” and “We Are The Robots”.

In the Transformers cartoon series of the early 1980’s, the voice of the character Soundwave was created using a vocoder. 

Tips For Using a Vocoder

The quality of a vocoder is mainly determined by the number of frequency bands that are used to analyse the voice. 16 is considered an acceptable minumum. Software vocoders often have a user-selectable number of bands – as many as 512, if the system CPU can handle the processing burden. The  Korg Microkorg’s synth keyboard’s vocoding ability was widely panned as it only had 8 channels. This was rectified in the Microkorg XL, which has a 16-band vocoder.

If you are trying to get a clear and recognisable voice out of your vocoder, you must use a wide spectrum (fat) sound source, like a sawtooth wave or a noise waveform. If you use a narrow-band source, you will barely get any sound output.

One of the most startling things when you first use a vocoder is realising that it completely ignores the pitch of your voice. Even if you sing an amazing 3-octave melody into the microphone, only a monotone will come out if that is what you have used as your sound source. This can also be a blessing in disguise. If you are a bad singer, but can play a perfect tune on the piano, your vocoded voice will be pitch perfect.

Use a vocoder like you would use a spice when cooking – they are good as a garnish, but bad as an ingredient. Many people find vocoders extremely annoying when they are overused.

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