<s>
The	O
source	B-Application
–	I-Application
filter	I-Application
model	I-Application
represents	O
speech	O
as	O
a	O
combination	O
of	O
a	O
sound	O
source	O
,	O
such	O
as	O
the	O
vocal	O
cords	O
,	O
and	O
a	O
linear	O
acoustic	O
filter	O
,	O
the	O
vocal	O
tract	O
.	O
</s>
<s>
While	O
only	O
an	O
approximation	O
,	O
the	O
model	O
is	O
widely	O
used	O
in	O
a	O
number	O
of	O
applications	O
such	O
as	O
speech	B-Application
synthesis	I-Application
and	O
speech	O
analysis	O
because	O
of	O
its	O
relative	O
simplicity	O
.	O
</s>
<s>
The	O
development	O
of	O
the	O
model	O
is	O
due	O
,	O
in	O
large	O
part	O
,	O
to	O
the	O
early	O
work	O
of	O
Gunnar	O
Fant	O
,	O
although	O
others	O
,	O
notably	O
Ken	O
Stevens	O
,	O
have	O
also	O
contributed	O
substantially	O
to	O
the	O
models	O
underlying	O
acoustic	O
analysis	O
of	O
speech	O
and	O
speech	B-Application
synthesis	I-Application
.	O
</s>
<s>
An	O
important	O
assumption	O
that	O
is	O
often	O
made	O
in	O
the	O
use	O
of	O
the	O
source	B-Application
–	I-Application
filter	I-Application
model	I-Application
is	O
the	O
independence	O
of	O
source	O
and	O
filter	O
.	O
</s>
<s>
In	O
such	O
cases	O
,	O
the	O
model	O
should	O
more	O
accurately	O
be	O
referred	O
to	O
as	O
the	O
"	O
independent	O
source	B-Application
–	I-Application
filter	I-Application
model	I-Application
"	O
.	O
</s>
<s>
Gunnar	O
Fant	O
,	O
a	O
pioneering	O
speech	O
scientist	O
,	O
used	O
Chiba	O
and	O
Kajiyama	O
's	O
research	O
involving	O
X-ray	O
photography	O
of	O
the	O
vocal	O
tract	O
to	O
interpret	O
his	O
own	O
data	O
of	O
Russian	O
speech	O
sounds	O
in	O
Acoustic	O
Theory	O
of	O
Speech	O
Production	O
,	O
which	O
established	O
the	O
source	B-Application
–	I-Application
filter	I-Application
model	I-Application
.	O
</s>
<s>
To	O
varying	O
degrees	O
,	O
different	O
phonemes	B-Language
can	O
be	O
distinguished	O
by	O
the	O
properties	O
of	O
their	O
source(s )	O
and	O
their	O
spectral	O
shape	O
.	O
</s>
<s>
In	O
implementation	O
of	O
the	O
source	B-Application
–	I-Application
filter	I-Application
model	I-Application
of	I-Application
speech	I-Application
production	I-Application
,	O
the	O
sound	O
source	O
,	O
or	O
excitation	O
signal	O
,	O
is	O
often	O
modelled	O
as	O
a	O
periodic	O
impulse	O
train	O
,	O
for	O
voiced	O
speech	O
,	O
or	O
white	O
noise	O
for	O
unvoiced	O
speech	O
.	O
</s>
<s>
Convolution	O
of	O
the	O
excitation	O
signal	O
with	O
the	O
filter	O
response	O
then	O
produces	O
the	O
synthesised	B-Application
speech	I-Application
.	O
</s>
<s>
The	O
source	O
produces	O
a	O
number	O
of	O
harmonics	O
of	O
varying	O
amplitudes	B-Application
,	O
which	O
travel	O
through	O
the	O
vocal	O
tract	O
and	O
are	O
either	O
amplified	O
or	O
attenuated	O
to	O
produce	O
a	O
speech	O
sound	O
.	O
</s>
