Vocoder

History

He was imagined by Homer Dudley, engineer with the Bell Laboratories, in order to ensure an effective transmission of the voice within the framework of the American phone network in 1939 under the name of voder ( Voice Operating DEmonstratoR ) which was presented to the World Fair of New York the same year. A version improved in 1940 will follow, the vocoder. With the first access, the vocodor had little success, because it gave to the voice a rather robot-like texture. It however was used by the US army in the first numerical communication system SIGSALY which allowed in particular Theodore Roosevelt and Winston Churchill to communicate beyond the ocean during the Second world war. In 1945 it is announced by Vannevar Bush in a famous article of As we may think which introduced the concept of World Wide Web (memex). In 1948, it will make of it a demonstration with the studios of WDR for Werner Meyer-Eppler, director of the Institute of Phonétique at the university of Bonn. This last was fascinated by the voice synthesizer and employed this first vocodor as bases for his writings which quickly became the bible of the German movement of Electronische Musik . Thus the vocodor was ready to be adopted like instrument.

Technique

The vocodor of Dudley cut out the voice in 12 bands of Fréquence S of which it measured the amplitude. These are the coefficients which were sent on the telephone cable. Other side by summoning the 12 balanced frequencies of the measured figures one obtained something of similar to the initial message. This process saves nearly 90% of Band-width. Indeed, the audio signal associated with the voice extends on the frequencies from 400 to 3400 Hz, that is to say a Band-width of 3000 Hz. By breaking up his spectrum into a dozen sub-bands of frequencies of different intensities definitely less broad, one can use only 300 Hz of total bandwidth.

Original technique of " voicecoder" is always used in music with certain standardized terms: Two signals, the carrier and the modulator passed in a bank of filters passebande. The amplitude of the modulator is measured via a " follower of enveloppe". The two signals are then modulated (multiplied) so that the envelope measured on the modulator is applied to the carrier. In this manner the characteristics of amplitude of a voice can be applied to a sound of synthetizer via a parallel circuit of (Master key bandages) * (Master key bande+suivor of amplitude)
More this circuit is reproduced in parallel plus the resynthèse modulator (the voice usually) will be precise. The technique of Vocodage can be also called " synthesis croisée".

Certain vocodeurs also allow to move the frequencies of the signal forming so that the voice becomes completely deformed and unrecognizable. this technique by exemble is used when anonymous a speaker should be made.

Note that one should not confuse Vocoder and PLEASE (super vocoder of Cooley/Tuckey phase) which does not use at all the technique of crossing of bank of BP filters, but of other complex techniques of analysis of samples based on the FFT (decomposition in sinusoid).

Musical application

After the Forties, the vocodor had only little application: only certain studio as those of BBC used some to propose particular sounds. But they are the musicians of the Années 1970 which will adapt it, thanks to the house EMS which manufactured a vocodor with dimensions and reasonable prices. Among them Kraftwerk, whose practically all compositions are decorated vocodées voices. But also Herbie Hancock, Roger Troutman, Giorgio Moroder, Electric Light Orchestrated, Matthias Jabs of Scorpions, Stevie Wonder and his wife Syreeta, Midnight Star, Pink Floyd or Joe Zawinul.

More recently, at the end of the Years 1990 and in the Years 2000, the vocodor included popularity thanks to certain compositions of Madonna, Kid Rock, Daft Punk and of Cher.

The group funk Zapp, on the other hand, used the Talkbox, an apparatus different from the Vocodeur - often comparable wrongly - which makes it possible to modulate a sound of Guitare or synthetizer with the mouth, through a tube.

Thus, the vocodor is known currently more like one instrument (or rather an effect) of musical creation or sound that like means of communication.

See too

external bonds

http://mysoundfreud.free.fr/ to manufacture its talkbox?
French-speaking http://mo.cheez.free.fr/ dedicated Forum. All on the talkbox.