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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

© 2000 Mark Huckvale University College London