ECHO, THE LOMBARD EFFECT, AND TIME DELAY

• Humans are used to hearing their voice while they speak - real-time feedback (side tone).
  
  
• When we place headphones over our ears, which dampens this feedback, we tend to speak louder.
  
  
• Lombard Effect: Humans speak louder in the presence of ambient noise.
  
  
• When this side-tone is delayed, it interrupts our cognitive processes, and degrades our speech.
  
  
• This effect begins at delays of approximately 250 ms.
  
  
• Modern telephony systems have been designed to maintain delays lower than this value (long distance phone calls routed over satellites).
  
  
• Digital speech processing systems can introduce large amounts of delay due to non-real-time processing.