Source Filter Model (1)(1)

7/30/2019 Source Filter Model (1)(1)

1/16

*


2/16

*

*A filter is anything that can selectively permit

some part of the signal to pass through and

block other parts.

*An acoustic filter selectively attenuates

(reduces in intensity) certain frequencies and

allows other frequencies to pass through

relatively unattenuated.


3/16

*

Speech is one of the most information-laidsignals.


4/16

*Voice production mechanism


5/16

*Speech sounds are sensations of air pressurevibrations produced by air exhaled from the lungsand modulated by the vibrations of the glottal cordsand the resonance of the vocal tract as the air ispushed out..

*Speech sounds have a rich and multi-layered

temporal-spectral variation that convey words,intention, expression, accent, speaker identity,gender, age and emotion.

*The combined voice production mechanismproduces the variety of vibrations and spectral-

temporal compositions that form different speechsounds.


6/16

*

The information is first modulated onto the passing

air by the manner and the frequency of closing and

opening of the glottal folds.

The output of the glottal fold is the excitation signal

to the vocal tract which is further shaped by the

resonances of the vocal tract and the effects of the

nasal cavities and the teeth and lips.


7/16

*

* Most of the filtering is carried out by that part of thevocal tract anterior to (to the front of) the soundsource.

*If the sound source is the glottis (in the larynx) then the

filter is the whole vocal tract from the larynx to themouth, and also to the nostrils if the velum is open.

*Sound sources can be periodic (e.g. voiced) or aperiodic(voiceless) or a mixture of both.

*Glottal sound sources can be periodic (voiced),

aperiodic (whisper and /h/) or mixed (e.g.breathyvoice).


8/16

*

*The source model of speech signals capturesand explains the detailed fine structure ofspeech spectrum.

*The source signal of speech is the noise-like air

from the lungs which is temporally andspectrally shaped by the manner and thefrequency of the openings and closings of theglottal folds.

*There are two broad types of speech sounds asshown in Figure voicedsounds like an e

pronounced as iy, and unvoicedsounds likes.


9/16

(a) Acoustic production of the word sea(pronounced s-iy),

(b) Spectrum of the unvoiced segment s, (c) spectrum of the voiced speech segment iy.


10/16

CONT.*First, as the air is pushed out from the lungs the vocal

cords are brought together, temporarily blocking the

airflow from the lungs and leading to increased sub-

glottal pressure.

*When the sub-glottal pressure becomes greater than

the resistance offered by the vocal folds, the folds

open and let out a pulse of air.

* Voiced sounds are produced by a repeating sequence

of opening and closing of glottal folds with a frequency

of between 40 (e.g. for a low frequency gravel malevoice) to 600 (e.g. for female childrens voice) cycles

per second (Hz) depending on the speaker,


11/16

CONT.

*The folds then close rapidly due to a combination offactors, including their elasticity, laryngeal muscle

tension, and the Bernoulli effect of the air stream.

*If the process is maintained by a steady supply of

pressurized air, the vocal cords will continue to open

and close in a quasi-periodic fashion.


12/16

*

*The window duration of excitationwaveform & phase of the glottal pulse isdefined as

U(t)=A(t) exp[ j(t-t0)W(t)] &

phase=[(t-t0)W(t)]

where U(t)=window duration

A(t)=time varying amplitude

W(t)=time varying frequency

t0 = onset time


13/16

*

*The movable structures associated withspeech production are also calledarticulators.*The tongue, lips, jaw, and velum are theprimary articulators.*Movement of these articulators appear toaccount for most of the variations in the

vocal tract shape associated with speaking.

*The glottis can be moved up or down toshorten or lengthen the vocal tract andhence change its frequency response


14/16

*

*The filter model captures and explains the envelopeof the speech spectrum.

*Due to reflective and resonance characteristic ofthe physical space, such as vocal tract, throughwhich a sound wave propagates changes thespectrum of sound.

* The vocal tract space composed of the oral and thenasal cavities and airways can be viewed as a time-varying acoustic filter that amplifies and filters the

sound energy and shapes its frequency spectrum.*The resonance frequencies of the vocal tract are

calledformants..


15/16

(a) a segment of the vowel ay, (b) its glottal excitation, and (c) its

magnitude Fourier transform and the frequency response of a linear prediction

model of the vocal tract.


16/16

*THANK YOU

Source Filter Model (1)(1)

Documents

Transcript of Source Filter Model (1)(1)