Examining speech production

As recording and examination apparatus improved it became clear that what had seemed like clearly identifiable distinct sounds of speech where in fact quite hard to classify based on the articulatory evidence alone. We will address this question fully in Section 7.3.2, but for now let 

Over the years a number of analysis tools have been developed to examine the production process. The first was the use of x-ray still photography, and then x-ray motion pictures. These techniques, especially the x-rays movies clearly showed the various articulators in motion. Unfortunately, the availability of x-ray movies is extremely limited due to the now imderstood harmful effects of x-ray e q)osure and hence this technique can not be used much. More recently a number of techniques have been developed. These include  

Electropalatography This involves the use of a plate fitted to the roof of the mouth, which measures contact between the tongue and palate. 

Electoglottography or laryngography This is the use of a device that fits around the neck and measures the impedance across the glottis. From this, a signal measuring glottal activity can be found. 

Air-flow measurement A mask and measuring apparatus can be used for measuring air flow from the mouth and separately from the nose. This is particularly useful in that we can measure the outputs from the nose and mouth separately, and we can do this in terms of air-flow signals rather than the pressure signals which microphones record. 

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The topic of speech production examines the processes by which humans convert hnguistic messages into speeeh. The converse process, whereby humans determine the message from the speech is called speech perception. Together these form the backbone of the field know as phonetics. In... 

An amplification caused by a filter is called a resonance, and in speech these resonances are known as formants. The frequencies at which resonances occur are determined solely by the position of the vocal tract they are independent of the glottis. So no matter how the harmonics are spaced, for a certain vocal tract position the resonances will always occur at the same frequencies. Different mouth shapes give rise to different patterns of formants, and in this way, the production mechanisms of height and loudness give rise to different characteristic acoustic patterns. As each vowel has a different vocal tract shape, it will have different formant pattern, and it is these that the listener uses as the main cue to vowel identity. The relationship between mouth shapes and formant patterns is complicated, and is fully examined in Chapter 11. 

Now that we have described the production process and the means by which discrete information can be encoded in a continuous signal, we turn to the issue of how speech sounds are organised linguistically. So far we have simply said that words are made from sequences of phonemes, but a closer examination will show however that it is far from the case that any sequence of phonemes... 

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