Exam Question Checklist

Exam 1999 Question 3

"Use the analogy of a bank of filters to describe how the spectrograph analyses speech signals. What is the difference between wide-band and narrow-band analysis? Which type of analysis is preferred for measuring formant frequencies and why?"

20 things you should mention:

• Spectrographic analysis
  • signal fed to each input of bank of filters
  • all band-pass
  • all same bandwidth
  • equally spaced in frequency
  • covers normal frequency range for speech 0-8kHz
  • axes are freq & time
  • energy at output of each filter expressed in dB
  • converted to grey scale
  • 3D picture reduced to 2D
• Wide and narrow
  • wide band - 300Hz
  • - good time resolution
  • - poor frequency resolution
  • narrow band - 45Hz
  • - poor time resolution
  • - good frequency resolution
• Formant analysis
  • wide band preferred
  • - smearing harmonics/harmonics don't get in way
  • - shows ringing of formants
  • narrow band shows harmonics
  • but harmonics don't necessarily coincide with formant frequencies