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Voiced Plosives

Overview

 

Voiced plosives are characterized by complete closure in the oral cavity, a build-up of pressure during which vibration of the vocal folds continues, and sudden release. The English phonemes /b/, /d/ and /g/ are distinguished from the voiceless plosives /ph/, /th/ and /kh/ in that:

Spectrogram Patterns for Voiced Plosives

Voiced plosives usually have voiced closures, and voicing is especially visible when the plosive is intervocalic. Voicing in word-initial closures is much less obvious; word-initial plosives often manifest neither closure nor burst. Consult Ladefoged for his discussion of voice onset time (VOT); for an example see figure 10.

The absence of a readily visible closure and burst is especially true with /b/, the weakest of all English plosives. When you cannot see a burst upon first examination but formants in a preceding phoneme seem to be dipping toward the bilabial position, look for rapid formant transitions going into the vowel after the possible plosive (10-20 ms). These short formant transitions indicate that the phone is a bilabial stop rather than the bilabial glide /w/ (slower moving, 30-50 ms) or nasal /m/ (slower still, 50-70 ms). These length estimates depend on the rate of the speaker and are based on CSLU's measurements of continuous speech.

Once you start entertaining the possibility of a voiced plosive in a spectrogram, take a look at the waveform; you will almost always see a blip indicative of a stop release just before the next phone begins. Another look at the spectrogram will reveal some spectral discontinuities accompanying the formant transitions.

The voiced closure, or voice bar, is sometimes confused with the nasal murmur or with the glide /w/. However, one way to tell the difference is by noting the height of these various F1 manifestations. A voiced closure is limited to a lower frequency range than a glide or a nasal. Therefore the amplitude of the voiced closure will also be lower. Taking a quick look at the waveform is the easiest way to measure amplitude. A voiced closure is on average half as high in frequency and in amplitude as a nasal. A glide at its widest point, on the other hand, is twice as high as a nasal. See an example of these differences in Figure 11. Because the nasal is quite regular across speakers, it is a good baseline phone with which to compare other segments. (NOTE: These measurements are based on Terri Lander's observations after looking at a lot of speech, not on any objective measurements.)

Word-initial closures in continuous speech average 50 ms in length, while word-final closures average 100 ms. Double plosives have a longer closure than single plosives.

Voiced bursts

Are voiced plosive bursts really voiced? Sometimes they do appear voiced, evidenced by formant bands in the short 10-20 ms burst. At other times it is unclear whether the burst you see is voiced. But one thing is certain: the voiced plosives are not aspirated anywhere near as much as the voiceless plosives.

Unaspirated voiced and voiceless bursts

Remember that in English, the voiceless stops /ph/, /th/, and /kh/ are aspirated unless they occur in certain predictable environments. Following /s/, /th/ will not be aspirated. But note that /d/ (the voiced counterpart to /th/) cannot follow /s/. So, once you know the context, you should not have too much trouble distinguishing between the allophonically unaspirated voiceless plosives and the normally unaspirated voiced plosives, because voiceless plosives become unaspirated in predictable environments, environments in which the voiced plosives cannot occur. Unaspirated voiceless plosives and voiced plosives are in complementary distribution in these cases: one group does not invade the other's turf.

The above is the ideal case.

The trouble starts where a voiceless plosive is not aspirated in an environment where we would expect it to be aspirated, or where voiced plosives have more aspiration than normal. Voiceless plosives become unaspirated in word-final position, due mainly to laziness, or possibly a shortage of breath! It is still not impossible to tell unaspirated (but released) word-final plosives from word-final released voiced plosives, though, because voiced plosives are often released with a schwa. If a voiceless plosive is released with a schwa, the burst is aspirated, and so what was lost has been found!

Long Vowels

Vowels preceeding voiced consonants are longer than vowels preceding voiceless consonants. The plosives are no exception. When deciding between voiceless and voiced plosives, consider vowel length.

Distinguishing Characteristics

The bilabial /b/

The alveolar /d/

The velar /g/

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next up previous index
Next: The Approximants (Glides and Up: Nasals and Plosives Previous: Voiceless Plosives

Ed Kaiser
Sat Mar 15 00:01:27 PST 1997