= Source-filter model of speech production
= Source-filter model
{synonym}
The <source-filter model of speech production> represents a speech sound as an acoustic source shaped by a filter describing the <vocal tract>. During voiced <speech>, vibration of the <vocal folds> supplies a roughly periodic source; constrictions can also generate noise. The tract's resonances emphasize particular frequency regions called <formants>.<Source-filter synthesis in the Praat Manual by Paul Boersma>[The source-filter theory of speech production; attribution to the 1960 acoustic theory]{ref}
<Paul Boersma> credits <Gunnar Fant>'s 1960 account as the theoretical basis of this construction.<Source-filter synthesis in the Praat Manual by Paul Boersma>[Section 1 and linked Fant (1960) bibliographic entry]{ref}
In a simplified linear model, output spectrum $Y(f)$ is $S(f)H(f)$, where $S$ describes the source and $H$ the tract's <transfer function>. Keeping the source fixed while changing the filter can change vowel quality without changing the source's fundamental repetition rate. The <Praat> tutorial makes this test concrete by constructing a source signal and a formant filter separately, then combining them. The model's separation is an approximation; real sources and tracts can interact.<Source-filter synthesis in the Praat Manual by Paul Boersma>[Filtering a source: independent source and FormantGrid construction and filtering]{ref}
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