Spoken Language systems

  There is a wide range of technologies which fall under the general banner of ``spoken language processing'' (SLP) including:

• ``automatic speech recognition '' ASR (also known as ``direct voice input'' DVI, and ``speech input'' SI),
• ``automatic speech generation'' ASG (also referred to as ``direct voice output'' DVO, ``speech synthesis''  SS, and ``text-to-speech'' TTS ),
• ``speech input/output'' SIO (which includes ``speech understanding systems'' SUS,
• ``spoken dialogue systems''  SDS, and ``speech-to-speech translation systems'' STS),
• ``speech coding'' (covering wide-band coding at over 4k bps, narrow-band secure voice between 1200 bps and 4k bps, and very-low data-rate speech communications at under 1200 bps),
• ``speech analysis or paralinguistic processing'' (which includes speaker identification/verification  , language identification/verification and topic spotting),
• general speech processing applications such as ``speech enhancement'' and ``voice conversion'', and ``speech systems technology'' (which is concerned with the technology of database recording, corpus transcription , annotation , storage and distribution).

Many of these technologies rely heavily on the availability of substantial quantities of recorded speech material: first, as a source of data from which to derive the parameters of their constituent models (manually or automatically), and second, in order to assess their behaviour under controlled (repeatable) test conditions. 

Of course very few spoken language processing applications involve stand-alone spoken language technology. Spoken language provides an essential component of the more general human-computer interface  alongside other input/output modalities such as handwriting, typing, pointing, imaging and graphics (see Figure 1.3). This means that the actions and behaviours of the speech-specific components of a spoken language system inevitably have to be orchestrated with respect to the other modalities and to the application itself by some form of interactive dialogue process (simultaneously taking into account the wide range of human factors involved).

The complexity of the human-computer interface , and the subtle role of speech and language processing within it, has been (and continues to be) a prime source of difficulty in deploying spoken language systems in ``real'' applications. Not only are field  conditions very different to laboratory  conditions, but there has been a serious lack of agreed protocols for testing  such systems and for measuring their overall effectiveness.

 
Figure 1.3: Multimodal human-computer interface  (HCI) including speech/language input/output