Vocoder

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The word “Sternzeit”, processed by a vocoder, first monophonic, then played with chords on a keyboard.

The vocoder (combination of the English voice and encoder ) is an electronic device that originates from military research and was developed for telephone technology in order to transmit natural language in encoded form as an analog signal on an electrical line and to reproduce it again at the destination. to be able to synthesize. Today the term is mainly associated with music: The vocoder is a device or software with which a speaking voice can be polyphonically modified using keys so that it sounds like an artificial choir.

In the military sector, the vocoder was used not only to encrypt the voice , but also to reduce the transmission bandwidth required for the audio signal, so that a larger number of calls can be conducted over a single subscriber line. The vocoder was mainly used in computer technology , in language research and as an effects device in popular and electronic music.

Historical vocoder used by the military for voice encryption

Vocoders are the basis of today's speech codecs, such as Code-Excited Linear Prediction (CELP), which aim to reduce the volume of speech signals without noticeable quality reduction.

Basics

Homer Dudley developed the prototype of this device in 1936 at Bell Telephone Laboratories , Murray Hill (New Jersey) . After technical improvements, primarily to the speech synthesis apparatus , the Voder (abbreviation for Voice Operation Demonstrator), the Vocoder was presented to the public in 1939. In 1960 Ernst Rothauser completed his dissertation on vocoder at the Vienna University of Technology. As a component of the Siemens synthesizer (equipment of the studio for electronic music ), the vocoder was first available for musical use in the early 1960s. But it wasn't until the late 1970s that vocoders became popular as a commercially produced effects device or stand-alone instrument equipped with a keyboard .

Working principle

Vocoder in the music sector as an effects device

The original functional principle is based on the breakdown of an input signal into its frequency components, the transmission of these components as a parameter set and the subsequent resynthesis of the signal at the target on the basis of the parameters from a noise signal. Thus, a vocoder has a recording unit (coder) for sound analysis and a playback part (voder) for sound synthesis. The working principle is based on the functioning of the human speech organ.

When used as an effects device, the output signal is not synthesized from noise, but a second input signal is modulated according to the spectral composition of the first signal. So two input signals are processed, which are linked by the vocoder. The second input signal corresponds to the vibration of the vocal cords in the human organ of speech; it supplies the basic signal (the so-called carrier ) from which the output signal is generated. The articulation through tongue and lip corresponds to the first input signal, it serves as a control signal for the sound spectrum and the modulation ( modulator ), whereby the spectrum of the first signal has a shaping effect on the second. With a voice signal as a control signal and an instrument signal to be modulated, it is possible, for example, to let an instrument “speak”.

In the vocoder, the fundamental frequency of the input signal is first extracted and used as a carrier. The sound spectrum is by means of a bandpass - filter bank split into separate frequency bands. In the individual bands, the respective amplitude curve is converted into a corresponding voltage by rectification . The voltages of all individual bands together represent the parameter set mentioned above. The accuracy of the sound analysis depends on the number of filters used and their frequency.

During synthesis, the carrier signal controls an oscillator that generates the fundamental oscillation, while with the help of a second filter bank, controlled by the voltage contours produced by the envelope followers, the analyzed sound spectrum is rebuilt on the basis of white noise.

Music practice

Vocoder for musicians

Vocoders in music practice are equipped with two inputs for different signals, each of which is subjected to the process described. This interconnection of the two input signals is a matrix , the control signals of which can also be exchanged or synchronized.

You can use it to replace the voice of a singer with an organ or string sound in such a way that a multi-part movement articulates the text of the song. By combining various input signals and technical manipulations, a wide range of sound options can be achieved with the human voice (e.g. robot or Mickey Mouse voices), but also various instrumental effects. The vocoder was a defining feature of the Düsseldorf band Kraftwerk .

The sound of a vocoder sometimes resembles and is confused with that of a harmonizer . Contrary to popular belief, the so-called “Cher effect” (heard for the first time on Chers Believe ) was not created with a vocoder, but with the help of the Antares Auto-Tune software or the corresponding device from the same manufacturer. Auto-tune is typically used to correct the pitch of poorly voiced vocals. The producers of the piece initially denied its use, probably in order not to associate Cher with poorly voiced singing.

Military use

The bijective transposition of frequency bands was of particular interest to communications technology and the military. In practical terms, this means that frequency bands were swapped (permuted) with one another, with the swapping being reversed by a spectral inverse function (e.g. Elcrovox). Today's digital voice encryption methods are much more complex; these hybrid algorithms also mostly contain compression .

literature

  • Friedrich Kittler : Grammophon Film Typewriter . Brinkmann & Bose, Berlin, 1986.
  • Mara Mills: Media and Prostheses: About the Artificial Larynx and the Vocoder. Sound machines between experiment and media technology , ed. Daniel Gethmann, Transcript Verlag, Bielefeld 2010, pp. 129–154, ISBN 978-3-8376-1419-0
  • Dave Tompkins: How to wreck a nice beach. The vocoder from World War II to Hip Hop. The machine speaks. Melville House, Brooklyn NY 2010, ISBN 978-1-933633-88-6 .
  • Thomas Sandmann : Effects & Dynamics. Professional know-how for mixing and mastering. The reference for beginners and professionals. 7th edition. PPV-Verlag, Bergkirchen 2008, ISBN 978-3-932275-57-9 .
  • Thomas Görne: Sound engineering. Fachbuchverlag Leipzig in Carl Hanser Verlag, Munich et al. 2006, ISBN 3-446-40198-9 .
  • Roland Enders: The home recording manual. The way to optimal recordings. 3rd, revised edition, revised by Andreas Schulz. Carstensen, Munich 2003, ISBN 3-910098-25-8 .
  • Ernst Rothauser: An impulse method for speech transmission based on the vocoder principle. Vienna (Vienna, Technical University, dissertation, 1960).

credentials

  1. ↑ Sonja Diesterhöft: Meyer-Eppler and the vocoder. In: Meyer-Eppler's research on electronic music. TU Berlin, 2003, accessed August 2020 .

Web links

Commons : Vocoders  - collection of images, videos and audio files