Exam Question Checklist

Exam 1998 Question 8

"Write short notes on ALL of the following: a) place coding of frequency; b) masking; c) beats."

20 things you should mention:

• Place Coding
  • cochlear structures: cochlea
    • basilar membrane
    • organ of corti / hair cells
  • BM mechanical properties vary with length
  • stimulus vibration causes BM to vibrate in sympathy
  • single place has matching resonant frequency
  • gives rise to maximum vibration: maximum nerve activity
• Masking
  • masking is interference in hearing mechanism
    • between components of a complex sound
  • threshold for one component affected by presence of another (or one component hides another)
  • caused by logarithmic coding of amplitude in cochlea
  • occurs when sounds close enough in frequency
    • within 1 critical distance (or 0.9mm)
  • and when one component is significantly more intense
• Beats
  • two sinusoidal signals
    • similar in frequency
  • gradually get in and out of phase with each other
  • at a rate related to their difference in frequency
  • seen as modulated amplitude envelope (picture)
  • gives rise to 'warbling' sensation