EQUAL LOUNDESS CURVES

• Just Noticeable Difference (JND): The acoustic value at which 75% of responses judge stimuli to be difference (also known as a difference limen).
  
  
• The perceptual loudness of a sound is specified via its relative intensity above the threshold. A sound's loudness is often defined in terms of how intense a reference 1 kHz tone must be heard to sound as loud.