Speech Production

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Speech Production
Introduction to Acoustics

• University of Salford
• Acoustics Audio and Video Group

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Learning Outcomes

• Explain how we produce speech sounds
• Explain the concepts of phonemes, voiced and
  unvoiced sound, vowels and formants
• Discuss a simple acoustic model of the voice

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Basic questions

• How do we make sound with the voice?
• How do we control this sound to talk?

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Organs of speech
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Speech sounds

• Phonation vocal folds vibrate periodically when
  air forced through them e.g. vowels
• Fricatives air forced through constriction in
  vocal tract e.g. s, f
• Plosives sharp close then open of vocal tract
  e.g. p
• Phonation is voiced, others are unvoiced

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Vocal folds open closed
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Model of phonation
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Characteristics of phonation
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Phonemes

• How to describe speech sounds?
• Is written language adequate?
• Phonetic symbols denote actual speech sounds
  phonemes
• Different phonemes are formed by using different
  combinations of nasal cavity, tongue and lips

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Phonetic alphabet

• See phoneme list, over

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Vowel sounds exercise

• By self-experimentation, determine the location
  of these vowel sounds on the chart opposite
• /i/ (heed)
• /?/ (had)
• /u/ (food)

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Formant frequencies
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Formants exercise

• There is a rough correlation between tongue
  position and the formant frequencies F1 and F2
• Study the formant table for /i/ and /a/ and see
  if you can label your previous vowel diagram

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Real speech time domain
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Spectrogram example
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Speech levels at 1 m, free field
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Directivity
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Dynamic range

• Usual assumption is 30 dB
• Experimental evidence for 50 dB or more
• (c/w 10-20 dB in cochlea implant)
• Normal hearing 60 correct words in sentences
  at 0 dB S/N 95 at 18 dB

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Speech synthesis
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Speech synthesis how?

• NLP
• large database of rules
• linguistics
• related to AI

• DSP
• ideal is physical model of vocal tract (like our
  one, but better)
• practice is recorded phonemes or combinations of
  phonemes

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Conclusions

• Simple model of voice source (glottal pulse) -gt
  variable filter (vocal tract)
• Phonemes are speech sounds
• Vowel sounds are identified by formant frequencies