Glottalisation

This video just has a plain transcript, not time-aligned to the videoThis video presents acoustic characteristics of glottalization with spectrographic and waveform illustrations. At the end of this video, you should be able to recognize and identify glottalization in the spectrogram based on visual appearance and begin to talk about some of the linguistic structures that might influence whether or not it is present in English.
The articulatory description of a phonetic glottal stop implies that the vocal folds must make a complete closure during production, but in reality there are a number of different sounds that are perceived and transcribed as glottal stops that do not show complete closure. Here is an example from Hawai’ian. The spectrograms shown here demonstrate two very different realizations of a glottal stop phoneme. On the top, we see an articulation that was produced with complete closure. We can see that it was produced with closure because there is no shading in the spectrogram between the end of the vowel [e] and the start of the vowel [u]. On the bottom, we see an articulation that did not involve complete closure. Instead, what we see is a change in the rate of vocal fold vibration. This is visible in the spectrogram as a change in how widely spaced the vertical striations are. In the first vowel [e], we can see that the glottal pulses are evenly and regularly spaced. As we approach the region transcribed as a glottal stop, we can see that the striations become more widely spaced before returning to a more regular vibration cycle for following vowel. In the case of Hawai’ian, both of these phonetic sounds indicate a phonemic contrast. They are allophones of a glottal stop phoneme. However, this change in the vibratory pattern of the vocal folds does not always indicate contrast in this way (or at all). In phonetic terms, we refer to this change in vocal fold vibration as glottalization.
Glottalization is known by many names including laryngealization, creaky voice, creaky phonation and vocal fry. There are several types of glottalization, but it is generally characterised by irregular and widely-spaced glottal pulses. It often, though not always, provides the auditory impression of ‘a rapid series of taps, like a stick being run along a railing’ (Catford, 1964)
Glottal stops and glottalization play many roles in many languages. They can sometimes convey meaningful contrast, either as a glottal stop phoneme, or as contrastive phonation on consonants or vowels, they can be correlated with tonal contrasts, or they can indicate the boundaries of prosodic phrases.
Although /ʔ/ is not a phoneme in English, phonetic glottal stops perform a variety of roles as well. In many varieties of English [ʔ] is an allophone of /t/. In the example I have provided here, the phonetic form of the word ‘kitten’ is produced with a glottal stop allophone for the /t/ phoneme. This is particular to my variety of English, so you might not produce a glottal stop allophone there depending on the variety of English that you speak. Nevertheless, if you listen carefully, you should be able to hear the phonetic glottal stop.
Phonetic glottal stops may also appear before vowels at the beginnings of prominent words, such as at the start of an utterance, or in stressed positions in the phrase. The example I have provided here is a transcription of the word “apple”. Try saying “apple” with and without a glottal stop at the start. Can you feel the closure at your glottis?
Some varieties of English also have glottal stops or glottalization that appears before voiceless oral stop closures. This is sometimes referred to as glottal reinforcement.
And finally, English also uses glottal stops and glottalization to indicate the ends of phrases.
In English, glottalization is often known as creak or creaky voice. The next few slides will show some examples of creak in English utterances for you to examine. Each of the figures has the same format. On the left, the orthographic form of the speech has been provided. The bottom of each figure shows a spectrogram of the speech. Above the spectrogram is a waveform. The wave form has been taken from the interval indicated by the angled line segments connecting the waveform diagram to the spectrogram.
The spectrogram on this slide was made of a recording of the phrase “trodden road”. The waveform corresponds to the area of the spectrogram outlined in orange. This portion of the utterance shows glottalization by the widely and irregularly spaced glottal pulses, corresponding to a low f0. We can also see the irregularity of the vibration in the waveform where there is a bit of a cyclical, repetitive pattern, but with clear irregularities.
Here is another example of glottalization in English. Again the waveform corresponds to the area outlined in orange. This time, the glottal pulses are more regularly spaced in time, but with a much lower rate of vibration than other nearby voiced intervals in the preceding vowels, outlined in blue
Here we have another example of glottalization. In this case, the vocal fold vibration is so irregular that there doesn’t even seem to be an identifiable cycle in the waveform.
Notice that in this case, the glottalization continues throughout much of the utterance. It is not limited only the highlighted area. In fact, it overlaps with a number of other phones. Notice also that the glottalization doesn’t always persist throughout the entire duration of a phone. For example, the first vowel starts of with regularly spaced glottal pulses, then transitions into irregularly spaced pulses before the oral stop closure. This illustrates the need for a separate annotation tier to capture the alignment of glottalisation among other speech gestures as they are occurring.
In this final example of glottalization in English, the waveform oscillations vary from cycle to cycle both in the length of the period and the amplitude of the wave. Once again, we can see that the magnified interval is not the only instance of creak in the utterance.
In fact, there appears to be (at least) two sources of glottalization in this case. At the end of the utterance, we see an extended interval of creak, likely indicating the end of a phrase. But we can also see shorter intervals of creak, such as at the start of prominent word “entirely” (and the end of the previous, outlined in blue.
In this video we have introduced various functions of glottalization, and noted that it can take a number of phonetic forms. We have looked at a number of spectrograms and waveforms showing glottalization in English utterances, and pointed out that it can overlap with other articulations of speech in a way that necessitates another layer of annotation. We have also seen examples of glottalization from more than one linguistic source relating to the prosodic structure of the phrase: prominence and prosodic phrase boundaries.