Pronunciation representations

In this section we shall define just what exactly the pronunciation component should do, what its input should be and what its output should be. 

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The formant synthesis technique just described is of course only half the problem in addition to generating waveforms from formant parameters, we have to be able to generate formant parameters from the discrete pronunciation representations of the type represented by the synthesis specification. It is useful therefore to split the overall process into separate parameter-to-speech (i.e. the formant synthesiser just described) and specification-to-parameter components. 

Perhaps unsurprisingly, the consensus as to where this point should be has shifted over the years. When more traditional systems were developed, memory was very tight and hence the number of base types had to be kept low regardless of any errors. In more recent years technological developments have eased the pressure on memory making more abstract representations possible. Given this, there is more choice over where exaetly the ideal representation should lie. In fact, as we shall see in Chapter 16, the most successfiil systems adopt a quite phonemic representation and avoid any rewriting to a phonetic space if at all possible. Because of this, the pronunciation component in modem systems is in fact much simpler than was perhaps the case in older systems, and quite often the input to the synthesiser is simply canonical forms themselves, direct from the lexicon. 

Finally, using a linear phonemic representation has the benefit that it makes automatic database labelling considerably easier. In Chapter 17 we shall consider the issue of labelling a speech database with phoneme units, both by hand and by computer. As we shall see, it is easier to perform this labelling if we assume a linear pronunciation model, as this works well with automatic techniques such as hidden Markov models. 

A vocabulary, a list of words that the program can recognize each word in the vocabulary has a text representation and a pronunciation... 

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