WS 2007 8 Speech Science VI Resonances Resonances

WS 2007 -8 Speech Science VI Resonances

Resonances Reading: Borden, Harris & Raphael, p. 95 -112 Kent p. 329 -343 Pompino-Marschall p. 102 -116 Reetz p. 33 -39

Recapitulation … and something new • The glottal waveform is a harmonically rich signal with energy in the whole frequency range important for speech. • So, the glottal waveform supplies the acoustic energy needed for all the different (voiced) speech sounds. We call it the “source“ for the speech signal • To form different sounds, the energy has to be modified into different patterns; The basic shape of the glottal excitation is (more or less) constant.

Source-Filter Model • The “source“ is filtered (modified) to produce different speech sounds: The glottal signal passes through a hollow space (the vocal tract) with specific resonator properties The resonator properties change according to the shape of the vocal tract.

Understanding resonance • The easiest way to understand resonances is to consider the vocal tract for the vowel [ ]: The vowel [ ] is produced with a neutral tongue shape (no extreme constrictions) Calculating resonances of a „uniform tube with one end closed and the other open“ shows that they are very similar to those found for [ ]

The principles of resonance 1 Resonance means favouring certain frequencies: WHY are some selected and others not? The pressure changes of some wavelengths (1, 3, 5 etc. ) fit better together than others (2, 4, 6 etc. )

The principles of resonance 2 Wavelengths with minimum pressure variation at the open end of the tube (lips) have some energy reflected and therefore die out less quickly. Minimum pressure change exists at the point of maximum deviation; i. e. for 1/4, 3/4, 5/4 , 7/4 etc of a cycle.

Calculating resonances The speed of sound is, say 340 metres per second … The length of our standard vocal tract (larynx to lips) is 17 cm. So, the frequency of the resonances are: R 1 = 0. 25 x 340 0. 17 = 500 Hz R 2 = 0. 75 x 340 0. 17 = 1500 Hz R 3 = 1. 25 x 340 0. 17 = 2500 Hz

Complexity of the vocal tract resonator Variation in the vertical cross-section Variation in the horizontal cross-section For calculation purposes the continually changing cross-sectional area is discretized

Resonances are NOT harmonics The vocal tract is heavily damped …. which means the filters are broad So several harmonics fall into the area of resonance. This is fortunate, because F 0 (and all the harmonics) change as the sentence tune changes.

Independence of filter from source Since resonances are a product of the vocal-tract shape, while the (periodic) excitation arises at the glottis, the two are independent of each other: Cf. same excitation, different resonance

Independence of filter from source 2 The relationship between source and filter is reversed in this case: We have a different excitation but the same resonance

Independence of filter from source 3 It is not necessary for the source to be periodic (which is important when you whisper)! Here we have noise excitation (continuous spectrum), the same resonance …. . but different damping.

Voice pitch vs. vowel quality Here we have three different glottal frequencies all supporting the same shape spectrum (in this case the vowel [i] Vowel demo

Cavities and vowel quality Vocal tract shape for the vowels in the words: (1) heed, (2) hid, (3) head, (4) had, (5) father, (6) good, (7) food. (from A Course in Phonetics, 1975, by Peter Ladefoged)

Cavities and vowel quality 2 Here the first and second formant frequency values (F 1 & F 2) are shown in relation to the pharynx cavity and the front oral cavity size, as well as to tongue height and position.

German vowels

Formant values for German vowels 1 2 3 4 Panels 1, 2 and 4 have the same F 1 values: higher values for more open vowels. Panel 3 shows very high F 1 for /a/ and /a: /. F 2 reflects size of front cavity: Back and liprounded vowels have lower F 2

How to remember formant values freq. F 2 F 1 i e E a A o u