= Speech synthesis
<Speech synthesis> generates an artificial <speech> signal from a specified representation. Text-to-speech starts from writing, while a research synthesizer can instead take a phonetic specification or directly controlled acoustic parameters. The distinction separates the input representation from the mechanism producing the sound.
In a <source-filter model of speech production>, a researcher can set an excitation's <fundamental frequency> and independently adjust the filter's <formants>. Holding the first parameter fixed while moving a <formant> tests whether listeners' responses depend on the spectral change rather than a change in voice pitch. <Gunnar Fant>'s work at KTH used synthesis to test hypotheses about <speech> production.<Human Speech and Communication at KTH>[research history, synthesis as a test of production hypotheses]{ref} Generated stimuli permit controlled comparisons in <speech perception>, but intelligibility and similarity to a natural speaker are different outcomes. Recording the parameter settings makes a synthesis experiment reproducible.
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