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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

© 2000 Mark Huckvale University College London