source filter model (1)(1)
TRANSCRIPT
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*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.
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Speech is one of the most information-laidsignals.
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*Voice production mechanism
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*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.
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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.
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* 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).
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*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.
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(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.
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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,
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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.
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*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
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*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
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*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..
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(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.
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*THANK YOU