Major speech sound categories

• Phonation is the technical term for the production of speech sounds. The source of the energy for almost all phonation is compressed air from the lungs. We say almost all because certain languages have clicks and other sounds which are ingressive (air flows in) rather than egressive (air flows out). In American English we can safely omit these cases, and speak only about the outflowing air from the lungs.
• When we are not speaking, we breathe about 15 times per second, and the two phases of inspiration (drawing the air in) and expiration (sending the air out) are approximately equal in duration.
• While speaking, we inhale quickly and make the expiratory phase of each breath cycle last for much longer than inspiration - up to 10 or 15 seconds in extreme cases. By moving various muscles, we systematically obstruct the passage of this air at the larynx and/or within the vocal tract, and thus give rise to speech.
• We have seen that all speech sounds powered by the lungs can be divided into three major categories, with certain phonemes combining sounds from more than one category, either simultaneously (voiced fricatives) or in sequence (closure-plosives):
  1. Voicing - The vocal cords are vibrating.
  2. Frication - There is constriction and therefore turbulence at some point in the vocal tract.
  3. Plosion - Air pressure builds up behind an articulator and is released in a sudden noisy burst.

  To complete the inventory of types of sounds used to create speech in American English, we add the fourth category silence, which is used in the closure phase of the plosives. Silence may also represent a period of breathing in at the end of an utterance or a deliberate pause in the speaker's speech stream.

• Today we look at voicing, which is perhaps the most complex of the three sound types, but also the most widely used. One estimate is that voicing occurs during 70 per cent of the total duration of an average utterance in American English. The good news for the spectrogram reader is that one can locate voicing almost infallibly in the spectrogram, if one knows what to look for.
• The following phoneme categories are almost always voiced:
  1. Vowels
  2. Diphthongs (moving vowels)
  3. Liquids
  4. Glides
  5. Nasals

  They are thus called sonorants , in opposition to the obstruents, that is, the fricatives, plosives, and affricates, whose primary function is viewed as obstructing the passage of air in significant ways rather than making the voice. Remember, however, that some obstruents are accompanied by voicing.

• We say that vowels are almost always voiced because all speech sounds may be unvoiced. Example of the whisper.
• Up until now we have defined voicing as the vibration of the vocal cords. This is true, but now we need to understand this vibration in more detail.