What is
a Vocoder

The Technical Stuff

A vocoder is a device that takes the sound of a modulator signal (usually human speech), measures changes in spectral characteristics over time, splits that signal into a number of frequency bands and creates amplitude envelopes for each band. The amp information for each band is then sent to a matching band-pass filter, where each band's level is determined and set to the corresponding frequency from the modulator signal. From here the carrier (noise source, synthesizer waveform), is processed through the filters and as such, the carrier is filtered so the harmonic content that comes through is reminiscent of the modulator (voice) signal. The result is as a less complex incarnation of the original voice. The whole process allows for a reduction in the amount of information required to store and transmit speech. You now only need a series of numbers, not a complete audio recording. Obviously the larger the number of frequency bands used, the more accurate the analysis and re-production (and the more data required).

History

Developed by physicist and Bell Labs engineer Homer Dudley in the late 1920's, the Vocoder was originally intended to make long distance communication easier by reducing signal bandwidth. This application wasn't very successful, as the process was deemed too expensive and speech clarity wasn't adequate.

But in 1942 the U.S. military commissioned Bell Labs to develop the system into a way of securing voice communications for use during World War II. For military purposes the U.S. was able to encrypt the control signals sent from the envelopes, used to facilitate the re-synthesis of the signal. By encrypting these signals they were able protect transmissions against interception. However by the late 1960's, several manufacturers had begun to build vocoder units for more creative purposes...

Vocoders In Music

We know that vocoders analyse the incoming signal by splitting it into frequency bands or ranges. Then use a carrier and corresponding set of band-pass filters to "re-synthesise" the original signal. Using something with rich harmonic content, such as a synthesiser as a carrier signal allowed people to modulate their voices in a very futuristic, inhuman way. This method also allowed easy control of the pitch of this modulation, making it very musical. Obviously this futuristic, robotic aesthetic appealed to early electronic musicians like Wendy Carlos and Kraftwerk, but by the late 80's the vocoder had made it's way into many different genres of music, being utilised by artists such as Afrika Bambaataa, Phil Collins, Neil Young, Michael Jackson, Herbie Hancock and countless disco and boogie tunes. To this day, it's still a popular tool in pop and electronic music, with the likes of Daft Punk being extremely well known for employing vocoder in their productions. In a wider sense, vocal modulation is more popular than ever as a creative technique with artists across the board using talk boxes, auto-tune and similar effects to change or "de-humanise" their voices.