Vocoder

The vocoder ( merge from the voice and encoder engl. ) Is an electronic device that comes from the military research and has been developed for the phone technology to transmit natural language in coded form as an analog signal on an electrical line and reproduce again at the destination or to synthesize. Today the term is brought mainly with music at: The vocoder is there a device or software, with which a speaking voice polyphonic keys can be modified so that it sounds like an artificial chorus.

In the military field, the vocoder was used to reduce the next voice encryption, the required transmission bandwidth of the audio signal, so that a larger number of calls over a single subscriber line can be performed. However, use of the vocoder found mainly in computer technology, in the language research and as an effects device in the popular and electronic music.

Vocoders are the basis of today speech codecs such as Code Excited Linear Prediction is ( CELP ), which have the goal to reduce voice signals in their data volume without any noticeable quality reduction.

Basics

The prototype of this device developed Homer Dudley in 1936 at the Bell Telephone Laboratories, Murray Hill (New Jersey). After technical improvements, primarily on the apparatus for speech synthesis, the V or ( acronym for Voice Operation Demonstrator ), the vocoder in 1939 presented to the public. 1960, Ernst Rothauser his dissertation on vocoder at the TU Vienna finished. As a part of the Siemens synthesizer ( equipment of the electronic music studio ), the vocoder was the early sixties the first time for musical use. But towards the end of the seventies found Vocoder as commercially produced effects unit or stand-alone instrument, equipped with a keyboard, distribution.

Principle of operation

The original principle is based on the decomposition of an input signal into its frequency components, the transfer of these components as a parameter set, and the subsequent resynthesis of the signal at the destination on the basis of the parameters of a noise signal. Thus a vocoder includes a receiving unit ( encoder ) for the sound analysis and a reproducing portion ( Voder ) for tone synthesis. The working principle is based on the workings of the human speech organ.

Effect when used as a device, the output signal is not synthesized from noise, but a second input signal is modulated to the spectral composition of the first signal accordingly. So it will be processed the two input signals by the vocoder linked. The oscillation of the vocal cords in the human body corresponding to the second speech input signal, and supplies the base signal ( the so-called carrier), from which the output signal is generated. The articulation of the tongue and the lip corresponds to the first input signal, it serves as a control signal for the sound spectrum and the modulating (modulator ), the spectrum of the first signal acts on the second shaping. With a voice signal as a control signal and a signal to be modulated instrument it is possible for example to "speak" a tool to let.

Vocoder the fundamental frequency of the input signal is first extracted and used as a carrier. The sound spectrum is divided by means of a bandpass filter bank into individual frequency bands. In each band is converted by the rectification of the respective amplitude characteristic into a corresponding voltage. The voltages of all individual bands put together the above-mentioned set of parameters represents the accuracy of the sound analysis depends on the number of filters used and their use frequency.

In the synthesis of the carrier signal control an oscillator which generates the fundamental oscillation, while with the aid of a second filter bank is controlled by the envelope follower brought forth by the voltage contours, the analyzed sound spectrum is reconstructed on the basis of white noise.

Music practice

Vocoder in the music practice are equipped with two inputs for different signals, each subjected to the process described above. The interconnection of the two input signals is a matrix, the control signals may be interchanged, or the same switch.

You can replace the voice of a singer by a organ or string sound so so, for example, that a more consistent rehearsed sentence articulates the lyrics. By combining various input signals and technical manipulations diverse sound possibilities with the human voice ( eg robots or Mickey Mouse voices ), but also various instrumental effects can be achieved. Character defining the vocoder was power plant at the Düsseldorf band.

The sound of a vocoder is similar to that of a harmonizer and sometimes is confused with this. Contrary to widespread opinion is the " Cher effect" created ( for the first time to listen to Cher's Believe) not with a vocoder, but with the help of the software Auto-Tune by Antares or the corresponding hardware device from the same manufacturer. Auto-Tune is normally used for pitch correction of bad intoniertem singing. The producers of the piece initially denied the use, probably not to bring Cher with bad intoniertem singing in conjunction.

For the telecommunications and the military in particular was the bijective transposition of frequency bands of interest. In practical terms, this means that frequency bands interchanged ( permuted ) were, with the interchange was to be undone by a spectral inverse function (eg Elcrovox ) together. Today's digital voice encryption methods are much more complex; also include these hybrid algorithms usually a compression.