If the modulating signal is continually changing in character, as is true of the human voice, these dynamic changes will be passed onto the carrier, giving the synth sound a recognisable vocal quality. Figure 1 shows a simplified block diagram of what's actually going on. In other words, the spectral characteristics of the modulating signal are duplicated in the filter bank processing the carrier. The signal to be modified, known as the carrier, is also fed to a bank of filters, but this time the level of signal passing through each filter band is modulated according to the output from the spectrum analyser section. The more filters in the bank, the more accurate the analysis. What really happens is this: the vocal signal, which we shall call the modulator, is analysed by a bank of filters that continually measure the signal envelope in each part of the spectrum in exactly the same way as a spectrum analyser does.
How A Vocoder WorksĪ vocoder enables the tonal character of one sound to be imposed on another, quite different sound the classic talking keyboard effect is produced by using the changing characteristics of the human voice to shape a sustained synth sound. Fortunately, a few multi‑effects units now include a vocoder as part of their repertoire, and with a little ingenuity, they can be used to modify sounds in a number of creative ways - other than producing the classic 'asthmatic who's swallowed a harmonica' vocal effect.īut before exploring some of the processing tricks made possible by this unique device, it's useful to take a look inside to see how it works. By the time MIDI started to take off, vocoders were all but extinct, with only a couple of manufacturers continuing to make them - which was a pity, because a vocoder really comes into its own when used as part of a MIDI system. Vocoders were very popular in the '70s, but their 'talking keyboard' sound soon became clichéd, and from then on, their popularity steadily declined. There's more to vocoders than 'Mister Blue Sky' - and with the vocoders supplied on some current multi‑effects processors, creative vocoding is now available to almost anyone.
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