the speech chain (denes pinson, 1993)

Tasko SPPA 6010 Advanced Speech Science

The Speech Chain (Denes & Pinson, 1993)


What information is embedded within the speech acoustic signal?

Phonetic information Affective information Personal information Transmittal information Diagnostic Information


Branches of science employed to understand speech communicationPhysics Acoustics Aerodynamics Kinematics Dynamics

Biology Anatomy

Gross anatomy Microscopic anatomy Molecular biology Neuroimaging

Physiology Electrophysiology


Physical Quantities Basic vs. Derived Scalar vs. Vector Area Volume Displacement Velocity Acceleration Force

Pressure Work Power Intensity Resistance

Ohm’s Law (V=IR)


Speech anatomy as “tubes” and “valves”

Speech production is achieved through the systematic regulation of air pressures and flows within the lungs and vocal tract.


Source-Filter Theory of Speech Production

The sounds we hear as speech is the product of a sound source that has undergone filtering by the vocal tract

source and the filter may be considered to be independent of each other


Source-Filter Theory


Sound: Acoustics review What is sound? Graphic representation of sound Classifying sounds Filters Resonance The decibel


What is sound? It may be defined as the propagation of a

pressure wave in space and time. propagates through a medium


What is sound? Mass-spring model


Wave action of molecular motionTime

1

2

3

4

5

Distance


Amplitude waveform

Position

Time


Amplitude waveform

Amplitude

Time

Question: How long will this last?


Model of air molecule vibrationTime

1

2

3

4

5

Distance

a b c d


Simple Harmonic Motion: Sine Wave

Features Amplitude Period Frequency

Hz octave

Phase

Pres

sure

Time


Graphic representation of sound Time domain

Called a waveform Amplitude v. time

Frequency domain Called a spectrum Amplitude spectrum

amplitude vs. frequency Phase spectrum

phase vs. frequency May be measured using a

variety of “window” sizes

Spectrogram frequency v. amplitude v. time


Same sound, different graphs

Time domain

Frequency domain

From Hillenbrand


Are all sound waves simply sinusoids?NO! Waves can be summed Simple waves can combine to produce complex waves Fourier: French Mathematician:

Any complex waveform may be formed by summing sinusoids of various frequency, amplitude and phase

Fourier Analysis Provides a unique (only one) solution for a given sound signal Is reflected in the amplitude and phase spectrum of the signal Reveals the building blocks of complex waves, which are sinusoids


Classification of sounds Number of frequency components

Simple Complex

Relationship of frequency components Periodic Aperiodic

Duration Continuous Transient


Complex periodic sounds: Graphic appearance

From Hillenbrand


Complex periodic sounds: Graphic appearance


Brief Digression


Amplitude vs. Phase Spectrum

Amplitude spectrum: different

Phase spectrum: same


Amplitude vs. Phase Spectrum

Amplitude spectrum: same

Phase spectrum: different


Digression concluded


Aperiodic sounds: Graphic appearance

From Hillenbrand


What “class” of sound is speech?


The “envelope” of a sound wave Amplitude envelope Spectrum envelope


Amplitude envelope

From Hillenbrand


Spectrum envelope

From Hillenbrand


Amplitude Spectrum: Window Size “instantaneous” amplitude spectrum (long term) average amplitude spectrum


“Instantaneous” Amplitude Spectra


(Long Term) Average Amplitude Spectrum


The Spectrogram


Rotate90 degrees

F

A F

A


Rotate it so thatThe amplitude isComing out of thepage

F

AThis is really narrow because it is a slice in time

F

Time


Dark bands= amplitudePeaks

Time

F


Two main types of spectrograms Wide-band spectrograms

Akin to spectrum envelopes “lined up” Frequency resolution not so sharp

Narrow-band spectrograms Akin to amplitude spectrums “lined up” Frequency resolution is really sharp


Highlights harmonic structure

Highlights spectrum envelope


Filters What is a filter? How are they relevant to speech? Frequency response curve Representing filter operation Types of filters


Frequency Response Curve (FRC)

Frequencylow high

Gai

n

+

-

Center frequency

lower cutofffrequency

upper cutoff frequency

passband

3 dB


Operation of a filter on a signal

NOTE: Amplitude spectrum describes a soundFrequency response curve describes a filter


Source-Filter Theory revisited


Some frequency selective filtersLow-pass filtersHigh-pass filtersBand-pass filters


Resonance What is resonance? Free vibration Forced vibration Acoustic resonators Resonance and speech Resonators as frequency selective filters


Resonance and Speech


Resonators as frequency selective filters


Measuring signal amplitude Amplitude vs. loudness Sound intensity vs. sound pressure Decibel scale

Linear vs. logarithmic Absolute vs. relative Reference values Deriving the equations

the speech chain (denes pinson, 1993)

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