Measuring Speech Privacy - Guidelines for Success

Though it may seem subjective, speech privacy can be measured, and the overall acoustical effectiveness of an environment can be objectively calculated. Our main tools of measurement are the Articulation Index (AI) and the Privacy Index (PI).

Articulation Index is a measurement of speech intelligibility, taking into account the following factors:

• The spectrum of normal human speech
  
• The sound attenuation (loss in intensity due to sound absorption and dispersal) between talker and listener
  
• The spectrum of background noise at the point of the listener.
  

The range of AI is between 0 and 1, where 0 indicates complete lack of intelligibility, and 1 indicates complete intelligibility.

Privacy Index is a measurement of speech privacy. PI can be derived from the AI measurement using the following formula:

PI = 100(1-AI)

The relationship between PI and AI is inverse (as the AI increases, the PI decreases) and nonlinear. The range of PI is between 0 and 100, where 0 indicates complete lack of privacy, and 100 indicates complete privacy.