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Department of Linguistics

Vocoders

Robert Mannell

Vocoders, also known as voice coders, are devices that take natural speech as their input and use that speech to generate various types of acoustic parameters which usually take up less transmission bandwidth that the original speech. These parameters are then transmitted to a re-synthesis device that re-generates the speech.

Vocoders have a long history, dating back to the late 1930's and were originally used as a means for compressing speech so that more speech signals (eg. telephone conversations) could take up the same bandwidth. Click here for an overview of the early history of vocoders.

Types of Vocoder

There are three main types of vocoder:

  1. Channel Vocoder
  2. Formant Vocoder
  3. LPC Vocoder

Issues in Vocoder Design

  1. Parametric Scaling in Vocoders

Vocoders and Speech Perception

  1. Effects of Time and Frequency Scaling on Speech Perception
  2. Effects of Vocoder Phase Characteristics on Speech Perception
  3. Effects of Intensity Scaling on Speech Perception (1991 paper)
  4. Effects of Intensity Scaling on Speech Perception (1992 paper 2)

Uses of Vocoders

  1. Speech data compression in telephony (including satellite telephony)
  2. Speech data compression for storage
  3. Speech Processing in Hearing Prostheses (Hearing Aids and Cochlear Implants)