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THE VOCODER

THE VOCODER. Outlines. What is a Vocoder? Background What does a Vocoder do? Modern Vocoders Applications. What is a Vocoder?. A Vocoder (a portmanteau of vox/voc (voice) and encoder) is a speech analyzer and synthesizer.

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THE VOCODER

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  1. THE VOCODER

  2. Outlines • What is a Vocoder? • Background • What does a Vocoder do? • Modern Vocoders • Applications

  3. What is a Vocoder? • A Vocoder (a portmanteau of vox/voc (voice) and encoder) is a speech analyzer and synthesizer. • It is a sound effect electronic instrument that can make a human voice sound synthetic. It is often used to speak like a robot, with a metallic and monotonous voice. • 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 digitized, encrypted and then transmitted on a narrow, voice-bandwidth channel. • The Vocoder has also been used extensively nowadays asan electronic musical instrument. Early 1970s vocoder, custom built by electronic music band Kraftwek

  4. Background • To put it simple: whenever you speak, your voice consists of two components. • Your basic voice type, produced by your vocal chords. • How you modulate the basic voice. • Example: Say a long "ohh". To accomplish this task, you nearly close your mouth. Next, say a long "ahh". This time, you opened your mouth. Your vocal chords produced the same sound for both, ohh and ahh but the modulation made it sound different. • The modulation signal is called formant (or modulator), because it forms and shapes the basic voice, which is called carrier due to the fact that it carries the formant signal. The formant signal carries the information and has a much lower frequency than the carrier, a circumstance that can be used to reduce bandwidth consumption for telephone services. This was also the original intention of a vocder.

  5. What does a Vocoder do? A Vocoder aims to replace the carrier of your voice with another carrier from another source.

  6. Modern Vocoder • Some modern Vocoders are implemented with built in (synthesizer or piano), from where the instrument carrier single is taken, while others have different carrier signals from other sources. • Input sources each may be file or soundcard (if supported) as for the output. If you use a soundcard as a source, please note: input is sampled in stereo but internally processed as two mono channels. One channel is considered to be the formant, the other the carrier. If your soundcard is duplex aware, you may even use it as source and destination at the same time. You can talk into the microphone and hear yourself at the same time. • If the no soundcard available, the input signal in this case is an audio file that will be vocoded by softwares or Matlab codes, not directly. • Basically the Vocoder theory is a type of signal processing and encoding together which based on EE 370, EE 430 and EE 406

  7. Applications • Several Vocoder systems are used in NAS encryption systems, such as Continuously Variable Slope Delta-modulation (CVSD) and others. • Television • Music • Film • Game applications

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