The vocoder (voice coder) derives from work in the telecommunications field to compress the human voice for more efficient transmitting over the telephone line. Bell Labs, among other companies, was working on vocoder technology back in 1950`s. This involved splitting of voice sound into separate frequency bands (just as found on the graphical equalizer of hi-fi sound systems) and using the output of each band to drive an amplifier applied to just one frequency band of an alternative input signal. In other words, the tone of the incoming voice was being superimposed on the pitch and level of a different incoming sound. When this was simple synthesized drone or buzz, the unexpected effect was that of a “speaking synthesizer”. It also took on the exact pitch of the incoming drone.
When it comes to its structure we can say that it needs two inputs. That is usually a voice plus, in musical applications, a synthesized sound, referred to as the modulator and the carrier respectively. The performer only has to speak, while playing the keyboard usually determines the melody. The more analysis filter bands vocoder has, the more intelligible output sound becomes. In earlier decades of 20th-century high-quality filters were expensive to build and so early vocoder designs were extremely costly. Just a couple of filters could create simple voice-like effects. The “Sparky’s Magic Piano” used this technique to apparently create a singing piano, with the BBC`s Radiophonic Workshop adopting these techniques very early on.
Both Walter Carlos and the TONTO duo managed to create a vocoder-like effect in the early 1970`s. However, the German experimental duo Kraftwerk commissioned a full custom vocoder around 1973. It appears on the track Ananas Symphonie on the Ralf and Florian album. Sennheiser in Germany and Harold Bode in the USA, who worked with Robert Moog, ALSO created expensive vocoder designs. After Kraftwerk’s worldwide success with the Autobahn album in 1974, they were able to buy and very imaginatively apply these
After finding a great deal of use in Techno and Dance music throughout the 1990’s, it falls out of fashion. When the digital synths such as Yamaha DX7 and Roland D50 largely replaced analog designs, the appearance of new models dried up. It was quickly realized that a digital signal processing intended to create reverb, delay, and other effects could just as effectively realize vocoder effect. So, it started to reappear as a gimmicky effect on inexpensive studio rack mounts. Later on, analog synths such as Quasimidi, Novation, Korg or Access appeared. The Access Virus kb became a vocoder of choice for Kral Bartos when he left the Kraftwerk. However, all of these lacked the individual controls of filter bands available on earlier analog designs.
After the analog revival, some other designs emerged. Including simple rack-mounts from MAM, Fat and the Next. These often included the monophonic sound source that was enough to reproduce the straightforward “robot voice”. This took it right back to basics, with separate analysis and synthesis sections, white noise generations, and a module to control hold and other parameters within the vocoder circuit design.
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