1. Hillenbrand: Source Filter Theory
Source-filter theory can be used to describe and explain any kind of speech – vowels, consonants, periodic, aperiodic, mixed, static, dynamic, you name it.
Our initial goal is to understand the application of SFT to just one simple thing: production of a sustained, phonated vowel. We’ll then see how SFT can be used to described anything and everything related to speech.
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Hillenbrand: Source Filter Theory

2. The Source of Source-Filter Theory (during phonated speech)

3. Hillenbrand: Source Filter Theory
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Hillenbrand: Source Filter Theory

4. Hillenbrand: Source Filter Theory
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Hillenbrand: Source Filter Theory

5. [ɑ]
[i]
[u]

6. Source-Filter Independence
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Hillenbrand: Source Filter Theory

7. Brad Story (University of Arizona) Source-Filter Demos
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Hillenbrand: Source Filter Theory

9. Source-Filter Theory Demonstration: Peter Frampton’s Talk Box

10. Questions
In what way does the Talk Box illustrate the principle of source-filter independence?
In what way does whispered speech illustrate the principle of source-filter independence?
Draw a source-filter theory model (source spectrum, VT FRC, and output spectrum) for the production of whispered speech, assuming that the source spectrum for whisper is white noise (which it isn’t, quite, but close enough).

11. Hillenbrand: Source Filter Theory
The source does not have to be the larynx and it does not have to be periodic. For example, the source for unvoiced fricatives is produced in the vocal tract rather than the larynx and is (roughly) white noise. The pictures below show SF models for /s/ and /ʃ/.
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Hillenbrand: Source Filter Theory

12. /s/ and /ʃ/ SF Models Overlaid
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Hillenbrand: Source Filter Theory

13. Hillenbrand: Source Filter Theory
Previous examples: Unvarying source, unvarying filter.
Everyday speech: Dynamic; i.e., source changes in pitch (f0), loudness (intensity), and quality (FRC) over time; filter varies over time as the articulators move.
Source-filter theory can accommodate the dynamic nature of speech simply by allowing the pitch, loudness, and detailed shape of the source to vary over time and by allowing the vocal tract FRC (i.e., the VT filter) to vary over time as the articulators move from one position to the next.
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Hillenbrand: Source Filter Theory

14. Time-Varying Source Spectrum
This is what the 1st part of time-varying source for “Where were you…” looks like in the frequency domain.
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Hillenbrand: Source Filter Theory

15. Time-Varying Source Waveform (i.e., time domain)
...
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Hillenbrand: Source Filter Theory

16. Time-Varying Vocal Tract Filter
Source Only Source Modified by Time-Varying Filter
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Hillenbrand: Source Filter Theory

17. Sinewave Speech Demonstration
Sinewave speech examples (from HINT sentence intelligibility test):
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Hillenbrand: Source Filter Theory

18. Sinewave Speech Example
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Hillenbrand: Source Filter Theory