Vocoder

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A vocoder, IPA: [ˈvoʊkoʊdər] (a portmanteau of the words voice and encoder), is an analysis / synthesis system, mostly used for speech in which the input is passed through a multiband filter, each filter is passed through an envelope follower, the control signals from the envelope followers are communicated, and the decoder applies these (amplitude) control signals to corresponding filters in the (re)synthesizer.

It was originally developed as a speech coder for telecommunications applications in the 1930s, the idea being to code speech for transmission. Its primary use in this fashion is for secure radio communication, where voice has to be encrypted and then transmitted. The advantage of this method of "encryption" is that no 'signal' is sent, but rather envelopes of the bandpass filters. The receiving unit needs to be set up in the same channel configuration to resynthesize a version of the original signal spectrum. The vocoder as both hardware and software has also been used extensively as an electronic musical instrument.

The vocoder is related to, but essentially different from, the computer algorithm known as the "phase vocoder".

Whereas the vocoder analyzes speech, transforms it into electronically transmitted information, and recreates it, the voder (from Voice Operating Demonstrator) generates synthesized speech by means of a console with fifteen touch-sensitive keys and a foot pedal, basically consisting of the "second half" of the vocoder, but with manual filter controls, needing a highly trained operator.[1]

Early 1970s vocoder, custom built for electronic music band Kraftwerk

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[edit] Vocoder theory

The human voice consists of sounds generated by the opening and closing of the glottis by the vocal cords, which produces a periodic waveform with many harmonics. This basic sound is then filtered by the nose and throat (a complicated resonant piping system) to produce differences in harmonic content (formants) in a controlled way, creating the wide variety of sounds used in speech. There is another set of sounds, known as the unvoiced and plosive sounds, which are not modified by the mouth in the same fashion.

The vocoder examines speech by finding this basic carrier wave, which is at the fundamental frequency, and measuring how its spectral characteristics are changed over time. This results in a series of numbers representing these modified frequencies at any particular time as the user speaks. In doing so, the vocoder dramatically reduces the amount of information needed to store speech, from a complete recording to a series of numbers. To recreate speech, the vocoder simply reverses the process, creating the fundamental frequency in an oscillator, then passing it through a stage that filters the frequency content based on the originally recorded series of numbers.

[edit] History

 Please help improve this article or section by expanding it. Further information might be found on the talk page. (October 2008)

[edit] Analog vocoders

Most analog vocoder systems use a number of frequency channels, all tuned to different frequencies (using band-pass filters). The various values of these filters are stored not as the raw numbers, which are all based on the original fundamental frequency, but as a series of modifications to that fundamental needed to modify it into the signal seen in the output of that filter. During playback these settings are sent back into the filters and then added together, modified with the knowledge that speech typically varies between these frequencies in a fairly linear way. The result is recognizable speech, although somewhat "mechanical" sounding. Vocoders also often include a second system for generating unvoiced sounds, using a noise generator instead of the fundamental frequency.

Please note that the description above is seriously misleading. Find another source!

The first experiments with a vocoder were conducted in 1928 by Bell Labs engineer Homer Dudley, who eventually patented it in 1935. Dudley's vocoder was used in the SIGSALY system, which was built by Bell Labs engineers (Alan Turing was briefly involved) in 1943. The SIGSALY system was used for encrypted high-level communications during World War II. Later work in this field has been conducted by James Flanagan.

[edit] Linear prediction-based vocoders

Since the late 1970s, most non-musical vocoders have been implemented using linear prediction, whereby the target signal's spectral envelope (formant) is estimated by an all-pole IIR filter. In linear prediction coding, the all-pole filter replaces the bandpass filter bank of its predecessor and is used at the encoder to whiten the signal (i.e., flatten the spectrum) and again at the decoder to re-apply the spectral shape of the target speech signal. In contrast with vocoders realized using bandpass filter banks, the location of the linear predictor's spectral peaks is entirely determined by the target signal and need not be harmonic, i.e., a whole-number multiple of the basic frequency.

More misleading description. For one thing, it is not true that the locations of the spectral peaks in a filter-bank vocoder need be at frequencies that are multiples of the fundamental.

[edit] Modern vocoder implementations

Even with the need to record several frequencies, and the additional unvoiced sounds, the compression of the vocoder system is impressive. Standard systems to record speech record a frequency from about 500 Hz to 3400 Hz, where most of the frequencies used in speech lie, which requires 64 kbit/s of bandwidth (the Nyquist rate). However a vocoder can provide a reasonably good simulation with as little as 2400 bit/s of data rate, a 26× improvement.

Several vocoder systems are used in NSA encryption systems:

  • LPC-10, FIPS Pub 137, 2400 bit/s, which uses linear predictive coding
  • Code Excited Linear Prediction, (CELP), 2400 and 4800 bit/s, Federal Standard 1016, used in STU-III
  • Continuously Variable Slope Delta-modulation (CVSD), 16 Kbit/s, used in wide band encryptors such as the KY-57.
  • Mixed Excitation Linear Prediction (MELP), MIL STD 3005, 2400 bit/s, used in the Future Narrowband Digital Terminal FNBDT, NSA's 21st century secure telephone.
  • Adaptive Differential Pulse Code Modulation (ADPCM), former ITU-T G.721, 32 Kbit/s used in STE secure telephone

(ADPCM is not a proper vocoder but rather a waveform codec. ITU has gathered G.721 along with some other ADPCM codecs into G.726.)

Vocoders are also currently used in developing psychophysics, linguistics, computational neuroscience and cochlear implant research.

[edit] Algebraic code-excited linear predictive codecs (ACELP 4.7 kbit/s – 24 kbit/s)

Voice Age

[edit] Mixed-excitation vocoders (MELPe 2400, 1200 and 600 bit/s)

Compandent

[edit] Multi-band excitation vocoders (AMBE 2000 bit/s – 9600 bit/s)

Digital Voice Systems Inc.

[edit] Sinusoidal-pulsed representation vocoders (SPR 300 bit/s – 4800 bit/s)

DSP Innovations Inc.

[edit] Musical applications

For musical applications, a source of musical sounds is used as the carrier, instead of extracting the fundamental frequency. For instance, one could use the sound of a synthesizer as the input to the filter bank, a technique that became popular in the 1970s.

[edit] Musical history

In 1969, electronic music pioneer Bruce Haack built one of the first truly musical vocoders. He named it 'Farad' after 1800's English chemist / physicist Michael Faraday and unlike its successors and predecessors, 'Farad' was programmed by touch and proximity relays. This invention was first used on Bruce Haack's album The Electronic Record for Children (1969), which was a DIY home pressing found mostly in libraries and elementary schools. In 1970 Wendy Carlos and Robert Moog followed with a 10-band device inspired by the vocoder designs of Homer Dudley, it was originally called a spectrum encoder-decoder, and later referred to simply as a vocoder. The carrier signal came from a Moog modular synthesizer, and the modulator from a microphone input. The output of the 10-band vocoder was fairly intelligible, but relied on specially articulated speech. Later improved vocoders use a high-pass filter to let some sibilance through from the microphone; this ruins the device for its original speech-coding application, but it makes the "talking synthesizer" effect much more intelligible.

Carlos and Moog's vocoder was featured in several recordings, including the soundtrack to Stanley Kubrick's A Clockwork Orange, in which the vocoder sang the vocal part of Beethoven's "Ninth Symphony". Also featured in the soundtrack was a piece called "Timesteps," which featured the vocoder in two sections. Originally, "Timesteps" was intended as merely an introduction to vocoders for the "timid listener", but Kubrick chose to include the piece on the soundtrack, much to the surprise of Wendy Carlos.[citation needed]

Bruce Haack's The Electric Lucifer (1970) was the first rock album to include the vocoder and was followed several years later by Kraftwerk's Autobahn. Another of the early songs to feature a vocoder was "The Raven" on the 1976 album Tales of Mystery and Imagination by progressive rock band The Alan Parsons Project; the vocoder also was used on later albums such as I Robot. Following Alan Parsons' example, vocoders began to appear in pop music in the late 1970s, for example, on disco recordings. Jeff Lynne of Electric Light Orchestra used the vocoder in several albums such as Time (featuring the Roland VP-330 Plus MkI). ELO songs such as "Mr. Blue Sky" and "Sweet Talking Woman" both from Out of the Blue (1977) use the vocoder extensively. Featured on the album are the EMS Vocoder 2000W MkI, and the EMS Vocoder (-System) 2000 (W or B, MkI or II).
"Mr. Blue Sky" by the Electric Light Orchestra (1977)
Classic example of a singing vocoded voice.
Problems listening to this file? See media help.

Pink Floyd made extensive use of the vocoder on the album Animals, even going so far as to put the sound of a barking dog through the device. Another example is Giorgio Moroder's 1977 album From Here to Eternity. Vocoders are often used to create the sound of a robot talking, as in the Styx song "Mr. Roboto". It was also used for the introduction to the Main Street Electrical Parade at Disneyland. The hard rock/metal band Avenged Sevenfold also used this effect for portions of the vocals on the song "Lost" from their self-titled album, released in 2008.

Vocoders have appeared on pop recordings from time to time ever since, most often simply as a special effect rather than a featured aspect of the work. However, many experimental electronic artists of the New Age music genre often utilize vocoder in a more comprehensive manner in specific works, such as Jean Michel Jarre (on Zoolook, 1984) and Mike Oldfield (on Five Miles Out, 1982). There are also some artists who have made vocoders an essential part of their music, overall or during an extended phase. Examples include the German synthpop group Kraftwerk, Stevie Wonder {"Send One Your Love," "A Seed's a Star"], jazz/fusion keyboardist Herbie Hancock during his late 1970s disco period, the synth-funk groups Midnight Star and The Jonzun Crew during the mid 1980s, French jazz organist Emmanuel Bex, Patrick Cowley's later recordings and more recently, avant-garde pop groups Trans Am, Black Moth Super Rainbow, Daft Punk, ROCKETS, Does It Offend You, Yeah?, The Medic Droid, electronica band The Secret Handshake, the Christian synthpop band Norway, as well as metal bands such as Vandal Known as Myth, At All Cost, Boots With Spurs and Cynic, electronica/progressive bands I See Stars and Breathe Carolina, and most recently Japanese electronica/dance band m.o.v.e (usually the vocoder was operated by the producer t-kimura).

Madonna often uses Vocoders for her albums and concerts including her 2001 Drowned World Tour, 2004 Re-Invention Tour, 2006 Confessions Tour, and her Sticky & Sweet Tour.

Recently Imogen Heap used a vocoder on her song "Hide and Seek". She plays full chords through her vocal without accompaniment. Anathema used a vocoder for singer Vincent Cavanagh in the song Closer from the A Natural Disaster (2003) album.

Geoff Downes, keyboardist for The Buggles, Yes, and Asia, has used the vocoder for such notable tunes as Tempus Fugit, from Yes' album Drama.

Other users of the vocoder include Prince, George Clinton, the late Roger Troutman, Teddy Riley, DeVante Swingand, T-Pain.

[edit] Other voice effects

See also: Robotic voice effects

"Robot voices" became a recurring element in popular music during the late twentieth century. Several methods of producing variations on this effect have arisen, of which the vocoder remains the best known and most widely-used.[citation needed] The following other pieces of music technology are often confused with the vocoder: the Talk box (Sonovox), Auto-Tune, Linear predictive coding, Ring modulation, Speech synthesis and Comb filter.

[edit] Television, film and game applications

[edit] Television

Vocoders have also been used in television, film and games usually for robots or talking computers. For example, the current Klasky Csupo closing logo "Robot", has a vocoder voiceover which is at the beginning, where as soon as the paint splashes on screen and a hand has placed a paper with a mouth on it. The vocoder voiceover says, "Klasky Csupo!", after that, 3-D blocks with the letters of the company name fly out of the face's mouth, the screen then cuts to black and we hear the "robotic" voice (off-screen) blubbering, then we hear a horn honking twice and finally a boinging sound. In the episode of Hollyoaks broadcast on Channel 4 on Friday 7 December 2007, Elliot and John Paul, posing as pirate broadcasters, used a vocoder which hacked into Kris' radio broadcast. The Cylons from Battlestar Galactica used the EMS Vocoder5000 and a ring-modulator to create their duo-tone voice effects. The 1980 version of the Doctor Who theme has a section generated by a Roland SVC-350 Vocoder. It is first obvious about 15 seconds into the theme. Also, in the early 1980s British sitcom Metal Mickey, used for the voice of Mickey, the robotic character.
Example of vocoder
Demonstration of the "robotic voice" effect found in film and television.
Problems listening to this file? See media help.

[edit] Films

One of the earliest film applications of vocoding can be heard in the flashback preludes of the 1949 movie A Letter to Three Wives. In several of the Transformers TV series (and 1986 animated film), some of the vocal effects (those for Soundwave being the most prominent example) were created with vocoders. In the film Sgt. Pepper's Lonely Hearts Club Band, the robotic singing of the Computerettes in the song "Mean Mr. Mustard" was achieved by using a vocoder.

[edit] Games

In Grand Theft Auto: San Andreas, a vocoder is used to disguise Mike Toreno's voice in a phone call to CJ. The phone call is received after completing the "Yay Ka Boom Boom" mission in San Fierro. In the game Half-Life 2 and its episodes trilogy, the main enemy, the Combine, talk in a sort of distorted sound, because Civil Protection units have vocoder in their masks, while transhuman soldiers and elites have the vocoder surgically implanted into their necks.

[edit] Analogue vocoder models

  • Analog-Lab X-32
  • Bode Model 7702
  • Bruce Haack Custom Model 'Farad'
  • Doepfer Modular Vocoder
  • Electro Harmonix Vocoder
  • Elektronika (Электроника) EM 26
  • EMS Vocoder 2000
  • EMS Vocoder 5000
  • FAT PCP-330 Procoder
  • Korg VC-10
  • Korg DVP-1 (Curtis Chip Filters)
  • Kraftwerk Custom Model (Above Photo)
  • Krok (Крок) 2401Vocoder (Вокодер)
  • MAM Vocoder VF11
  • Moog Modular Vocoder
  • Moog Vocoder [Bode]
  • Next! VX-11 Vocoder
  • PAiA 6710 Vocoder
  • Roland SVC-350
  • Roland VP-330
  • Sennheiser VSM-201
  • Synton Syntovox 202
  • Synton Syntovox 216
  • Synton Syntovox 221
  • Synton Syntovox 222

[edit] Hardware DSP vocoder models

  • Access Virus C Series [32-band]
  • Alesis Akira
  • Alesis Ion [40-band]
  • Alesis Metavox
  • Alesis Micron [40-band]
  • Behringer 2024 DSP Virtualizer Pro
  • Digitech S100/S200
  • Digitech StudioQuad 4
  • Electrix Warp Factory
  • Korg microKorg
  • Korg MS2000 [16-band]
  • Korg RADIAS
  • Korg R3
  • Novation K-Station KS4 / KS5 / KS Rack [12-band]
  • Novation Nova [40-band]
  • Quasimidi Sirius
  • Red Sound Vocoda
  • Red Sound Darkstar
  • Roland Juno-Stage [10-band]
  • Roland SP-808 [10-band]
  • Roland JP-8080 [12-band]
  • Waldorf Q
  • Zoom Studio 1201

[edit] Software vocoder models

  • Arboretum Systems Ionizer
  • Arturia Vocoder
  • Fruity Vocoder
  • Opcode Fusion Vocode
  • Native Instruments Vokator
  • Propellerheads Reason BV-512 [4 to 512-band]
  • Prosoniq OrangeVocoder
  • RoVox
  • Sirlab
  • VirSyn MATRIX Vocoder
  • Zerius

[edit] See also

[edit] References

[edit] Cited references

  1. ^ Wendy Carlos about vocoders

[edit] External links

Retrieved from "http://en.wikipedia.org/wiki/Vocoder"
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