Chapter 16: Language and Computers

Speech Synthesis

• Speech synthesis- the use of a machine, usually a computer, to produce human-like speech
• Canned speech- prerecorded utterances and phrases
• Synthesized speech- piecing together smaller recorded units of speech into new utterances
• Intelligibility- how well listeners can recognize and understand the individual sounds or words generated by the synthesis system
• Naturalness- how much the synthesized speech sounds like the speech of an actual person
• Articulatory synthesis- a synthesis technique that generates speech “from scratch” based on computational models of the shape of the human vocal tract and the articulation processes
• Source-filter theory- there are two independent parts to the production of speech sounds
  • Source- the mechanism that creates a basic sound
  • Filter- shapes the sound created by the source into the different sounds we recognize as speech sounds
• Concatenative Synthesis- uses recorded speech by stringing together pieces of the recorded speech and then smoothing the boundaries between them
  • Unit selection synthesis- takes large samples of speech and builds a database of smaller units from these speech samples
  • Diphone synthesis- pairs of adjacent sounds are attached at the end of one phone and the beginning of another
  • Domain-specific synthesis- create utterances from prerecorded words and phrases that closely match the words and phrases that will be synthesized
• Text-to-speech synthesis- speech generated directly from text entered with normal orthography

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Automatic Speech Recognition

• Automatic Speech Recognition- the conversion of an acoustic speech waveform into text
• Noisy channel model- treats speech input as if it has been passed through a communication channel that garbles the speech waveform
• @@Components of an Automatic Speech Recognition System:@@
  • Signal processing- recording the speech waveform with a microphone and storing it in a manner that is suitable for further processing by a computer
  • Acoustic modeling- mapping the energy values extracted during signal processing
  • Pronunciation modeling- used to filter out unlikely sound sequences
  • Language modeling- calculating the probability of sequences
• @@Parameters of Speech Recognition Systems@@
  • Speaking mode- only accepts isolated word input or continuous speech input
  • Vocabulary size- the size of the system’s vocabulary will impact its accuracy
  • Speaker Enrollment- the system may or may not need to be trained to a specific voice

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Communicating with Computers

• Interactive Text-Bases Systems- dialogue carried between computer and user via text
  • Word spotting- a program focuses on words it knows and ignores ones it doesn’t
• Spoken-Language Dialogue Systems- Dialogue carried between computer and user via speech
  • Isolated speech- the user speaks the input clearly and without extraneous words
  • Continuous speech- input can be more like normal speech
• Components of a Spoken-language Dialogue System
  • Automatic Speech Recognition- combining levels of linguistic knowledge in order to allow speaker-independent understanding of continuous speech
  • @@Language Processing and Understanding@@- the system must decipher not only individual words, but also the intention of the speaker
  • @@Dialogue Management@@- the system needs to understand the intentional structure of the conversation
  • @@Text Generation@@- the use of computers to respond to humans using natural language by creating sentences that convey the relevant information
  • @@Speech Synthesis@@- the words that make up the generated text must be converted into a sequence of sounds

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Machine Translation

• Translation- the task of converting the contexts of a text written in one language into a text in another language
• Machine translation- the use of computers to carry our translation
• Problems:
  • Context can often be removed
  • Lexical ambiguity
• Partial Automation- the source language text can first be pre-edited by a person so as to “prime” it for a machine translation system

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Corpus Linguistics

• Corpus- a collected body of text
• Corpus linguistics- involves the design and the annotation of corpus materials that are required for specific purposes
• Corpus can be composed from spoken, signed or written language
• Corpora can be classified by the genre of the source material
• Balanced corpora- corpora that try to remain balanced among different genres
• Reference corpus- specified amount of text that has been collected and annotated
• Monitor corpus- as new texts continue to be written or spoken, more data is gathered

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