Acoustic Characteristics of Vowels

Acoustic Characteristics of Vowels

Robert A. Prosek, Ph.D.CSD 301

Robert A. Prosek, Ph.D.CSD 301

F2-F1 DisplaysF2-F1 Displays•Formant frequencies are determined by the

articulation

•If the articulation changes, the formant frequencies should change

•The F2-F1 display shows the second formant frequency on the ordinate and the first formant frequency on the abscissa

•The parameter is a particular vowel

•Peterson and Barney (1952) and Hillenbrand, Clark, Getty, and Wheeler (1995) are the primary references for vowel spaces

•Formant frequencies are determined by the articulation

•If the articulation changes, the formant frequencies should change

•The F2-F1 display shows the second formant frequency on the ordinate and the first formant frequency on the abscissa

•The parameter is a particular vowel

•Peterson and Barney (1952) and Hillenbrand, Clark, Getty, and Wheeler (1995) are the primary references for vowel spaces

Models of VowelsModels of Vowels• In addition to the linear source-filter theory, models of vowels attempt to

explain the relationship between vowel production and vowel perception

• The target model of Lindbloom was one of the early attempts

• Vowel articulations are considered invariant or canonical

• Because different formant frequencies lead to the perception of the same vowel, normalization is needed

• Not simple

• Separate normalizations are needed for different areas of the vocal tract

• Vowels also differ in duration and formant frequency trajectories

• Normalization in terms of mels or Barks

• these are non-linear transformations based on audition

• not well adopted, but research indicates that Barks have a role

• In addition to the linear source-filter theory, models of vowels attempt to explain the relationship between vowel production and vowel perception

• The target model of Lindbloom was one of the early attempts

• Vowel articulations are considered invariant or canonical

• Because different formant frequencies lead to the perception of the same vowel, normalization is needed

• Not simple

• Separate normalizations are needed for different areas of the vocal tract

• Vowels also differ in duration and formant frequency trajectories

• Normalization in terms of mels or Barks

• these are non-linear transformations based on audition

• not well adopted, but research indicates that Barks have a role

Models of Vowels (2)Models of Vowels (2)

•Dynamic specification model

•transitions of formant frequencies

•duration

•F2-F1 chart inadequate

•Dynamic specification model

•transitions of formant frequencies

•duration

•F2-F1 chart inadequate

Vowel Formant PatternVowel Formant Pattern• The pattern of vowel formant frequencies determines the perception

of the vowel

• However, static patterns may not be necessary

• The standard deviations in Tables 4-1 and 4-1 intersect, for example

• But, for any one individual, there must be some separation among the vowels in F2-F1 space

• Remember the acoustic-phonetic rules for vowels

• F1 varies inversely with tongue height

• F2 varies directly with tongue advancement

• F2-F1 space can be transformed

• Bark scale

• ERB scale

• The pattern of vowel formant frequencies determines the perception of the vowel

• However, static patterns may not be necessary

• The standard deviations in Tables 4-1 and 4-1 intersect, for example

• But, for any one individual, there must be some separation among the vowels in F2-F1 space

• Remember the acoustic-phonetic rules for vowels

• F1 varies inversely with tongue height

• F2 varies directly with tongue advancement

• F2-F1 space can be transformed

• Bark scale

• ERB scale

Short-Time Spectra for VowelsShort-Time Spectra for Vowels•Spectral variations are important

•Spectral tilt

•Depth of valleys

•Logarithmic changes

•Relative position of spectral peaks

•Changes in slope near peaks

•LTASS

•Widely used in Europe, especially for voice disorders

•Many similarities across languages

•Spectral variations are important

•Spectral tilt

•Depth of valleys

•Logarithmic changes

•Relative position of spectral peaks

•Changes in slope near peaks

•LTASS

•Widely used in Europe, especially for voice disorders

•Many similarities across languages

Vowel DurationVowel Duration

•Tense-lax distinction

•Vowel height

•Syllable stress

•Speaking rate

•Voicing of the preceding or following vowel

•Place of articulation of surrounding sounds

•Word familiarity

•Tense-lax distinction

•Vowel height

•Syllable stress

•Speaking rate

•Voicing of the preceding or following vowel

•Place of articulation of surrounding sounds

•Word familiarity

Vowel Fundamental FrequencyVowel Fundamental Frequency

•If other factors are controlled, vowels appear to have an intrinsic f0

•f0 varies directly with vowel height

•Probably not critically important, but it does add naturalness to speech

•What is the physiology that causes these f0 changes?

•If other factors are controlled, vowels appear to have an intrinsic f0

•f0 varies directly with vowel height

•Probably not critically important, but it does add naturalness to speech

•What is the physiology that causes these f0 changes?

Formant Bandwidths and Amplitudes

Formant Bandwidths and Amplitudes

• Formant bandwidth and amplitude interact

• Bandwidth is related to damping

• Damping is the rate of absorption of sound energy

• As damping increases, bandwidth increases and sound waves’ amplitudes decrease quickly

• In general, bandwidth increases as formant number increases

• Changing bandwidth does not affect vowel identification

• Changing bandwidth might influence quality, however

• Discrimination among vowels may be enhanced by changes in bandwidth

• Formant bandwidth and amplitude interact

• Bandwidth is related to damping

• Damping is the rate of absorption of sound energy

• As damping increases, bandwidth increases and sound waves’ amplitudes decrease quickly

• In general, bandwidth increases as formant number increases

• Changing bandwidth does not affect vowel identification

• Changing bandwidth might influence quality, however

• Discrimination among vowels may be enhanced by changes in bandwidth

Formant Bandwidths and Amplitudes

Formant Bandwidths and Amplitudes

•An increase in bandwidth often leads to a decrease in amplitude for a particular formant frequency

•Formant amplitudes are determined by

•Formant frequency

•Formant bandwidth

•Energy available from the source

•Again, all of the acoustic energy for vowels comes from the source (vocal fold vibrations)

•An increase in bandwidth often leads to a decrease in amplitude for a particular formant frequency

•Formant amplitudes are determined by

•Formant frequency

•Formant bandwidth

•Energy available from the source

•Again, all of the acoustic energy for vowels comes from the source (vocal fold vibrations)

DiphthongsDiphthongs

•For diphthongs, there is no single vocal tract shape that characterizes the articulation

•Diphthongs are usually described as having an on-glide and an off-glide

• If the articulation changes during the production of a diphthong, then the formant frequencies change as well

•The actual formant frequencies realized depends on the speaking rate

•The rate of formant frequency change, however, obtains no matter what the speech rate

•For diphthongs, there is no single vocal tract shape that characterizes the articulation

•Diphthongs are usually described as having an on-glide and an off-glide

• If the articulation changes during the production of a diphthong, then the formant frequencies change as well

•The actual formant frequencies realized depends on the speaking rate

•The rate of formant frequency change, however, obtains no matter what the speech rate