<s>
A	O
harmonic	O
sound	O
is	O
said	O
to	O
have	O
a	O
missing	B-Application
fundamental	I-Application
,	O
suppressed	B-Application
fundamental	I-Application
,	O
or	O
phantom	B-Application
fundamental	I-Application
when	O
its	O
overtones	O
suggest	O
a	O
fundamental	O
frequency	O
but	O
the	O
sound	O
lacks	O
a	O
component	O
at	O
the	O
fundamental	O
frequency	O
itself	O
.	O
</s>
<s>
A	O
low	O
pitch	O
(	O
also	O
known	O
as	O
the	O
pitch	O
of	O
the	O
missing	B-Application
fundamental	I-Application
or	O
virtual	O
pitch	O
)	O
can	O
sometimes	O
be	O
heard	O
when	O
there	O
is	O
no	O
apparent	O
source	O
or	O
component	O
of	O
that	O
frequency	O
.	O
</s>
<s>
It	O
was	O
once	O
thought	O
that	O
this	O
effect	O
was	O
because	O
the	O
missing	B-Application
fundamental	I-Application
was	O
replaced	O
by	O
distortions	O
introduced	O
by	O
the	O
physics	O
of	O
the	O
ear	O
.	O
</s>
<s>
However	O
,	O
experiments	O
subsequently	O
showed	O
that	O
when	O
a	O
noise	O
was	O
added	O
that	O
would	O
have	O
masked	O
these	O
distortions	O
had	O
they	O
been	O
present	O
,	O
listeners	O
still	O
heard	O
a	O
pitch	O
corresponding	O
to	O
the	O
missing	B-Application
fundamental	I-Application
,	O
as	O
reported	O
by	O
J	O
.	O
C	O
.	O
R	O
.	O
Licklider	O
in	O
1954	O
.	O
</s>
<s>
The	O
pitch	O
of	O
the	O
missing	B-Application
fundamental	I-Application
,	O
usually	O
at	O
the	O
greatest	O
common	O
divisor	O
of	O
the	O
frequencies	O
present	O
,	O
is	O
not	O
,	O
however	O
,	O
always	O
perceived	O
.	O
</s>
<s>
Research	O
conducted	O
at	O
Heidelberg	O
University	O
shows	O
that	O
,	O
under	O
narrow	O
stimulus	O
conditions	O
with	O
a	O
small	O
number	O
of	O
harmonics	O
,	O
the	O
general	O
population	O
can	O
be	O
divided	O
into	O
those	O
who	O
perceive	O
missing	B-Application
fundamentals	I-Application
,	O
and	O
those	O
who	O
primarily	O
hear	O
the	O
overtones	O
instead	O
.	O
</s>
<s>
The	O
authors	O
used	O
structural	O
MRI	B-Algorithm
and	O
MEG	B-Algorithm
to	O
show	O
that	O
the	O
preference	O
for	O
missing	B-Application
fundamental	I-Application
hearing	O
correlated	O
with	O
left-hemisphere	O
lateralization	O
of	O
pitch	O
perception	O
,	O
where	O
the	O
preference	O
for	O
spectral	O
hearing	O
correlated	O
with	O
right-hemisphere	O
lateralization	O
,	O
and	O
those	O
who	O
exhibited	O
the	O
latter	O
preference	O
tended	O
to	O
be	O
musicians	O
.	O
</s>
<s>
Timpani	O
produce	O
inharmonic	O
overtones	O
,	O
but	O
are	O
constructed	O
and	O
tuned	O
to	O
produce	O
near-harmonic	O
overtones	O
to	O
an	O
implied	O
missing	B-Application
fundamental	I-Application
.	O
</s>
<s>
A	O
timpani	O
might	O
be	O
tuned	O
to	O
produce	O
sound	O
most	O
strongly	O
at	O
200	O
,	O
302	O
,	O
398	O
,	O
and	O
488Hz	O
,	O
for	O
instance	O
,	O
implying	O
a	O
missing	B-Application
fundamental	I-Application
at	O
100Hz	O
(	O
though	O
the	O
actual	O
dampened	O
fundamental	O
is	O
170Hz	O
)	O
.	O
</s>
<s>
Because	O
of	O
the	O
missing	B-Application
fundamental	I-Application
effect	O
,	O
the	O
fundamental	O
frequencies	O
of	O
male	O
voices	O
are	O
still	O
perceived	O
as	O
their	O
pitches	O
over	O
the	O
telephone	O
.	O
</s>
<s>
The	O
missing	B-Application
fundamental	I-Application
phenomenon	I-Application
is	O
used	O
electronically	O
by	O
some	O
pro	O
audio	O
manufacturers	O
to	O
allow	O
sound	O
systems	O
to	O
seem	O
to	O
produce	O
notes	O
that	O
are	O
lower	O
in	O
pitch	O
than	O
they	O
are	O
capable	O
of	O
reproducing	O
.	O
</s>
<s>
In	O
a	O
hardware	O
effects	O
unit	O
or	O
a	O
software	O
plugin	B-Application
,	O
a	O
crossover	B-Algorithm
filter	I-Algorithm
is	O
set	O
at	O
a	O
low	O
frequency	O
above	O
which	O
the	O
sound	O
system	O
is	O
capable	O
of	O
safely	O
reproducing	O
tones	O
.	O
</s>
<s>
Musical	O
signal	O
content	O
above	O
the	O
high-pass	O
part	O
of	O
the	O
crossover	B-Algorithm
filter	I-Algorithm
is	O
sent	O
to	O
the	O
main	O
output	O
which	O
is	O
amplified	O
by	O
the	O
sound	O
system	O
.	O
</s>
<s>
Low	O
frequency	O
content	O
below	O
the	O
low-pass	O
part	O
of	O
the	O
crossover	B-Algorithm
filter	I-Algorithm
is	O
sent	O
to	O
a	O
circuit	O
where	O
harmonics	O
are	O
synthesized	O
above	O
the	O
low	O
notes	O
.	O
</s>
<s>
This	O
very	O
concept	O
of	O
"	O
missing	B-Application
fundamental	I-Application
"	O
being	O
reproduced	O
based	O
on	O
the	O
overtones	O
in	O
the	O
tone	O
has	O
been	O
used	O
to	O
create	O
the	O
illusion	O
of	O
bass	O
in	O
sound	O
systems	O
that	O
are	O
not	O
capable	O
of	O
such	O
bass	O
.	O
</s>
<s>
In	O
mid-1999	O
,	O
Meir	O
Shashoua	O
of	O
Tel	O
Aviv	O
,	O
co-founder	O
of	O
Waves	O
Audio	O
,	O
patented	O
an	O
algorithm	O
to	O
create	O
the	O
sense	O
of	O
the	O
missing	B-Application
fundamental	I-Application
by	O
synthesizing	O
higher	O
harmonics	O
.	O
</s>
<s>
Waves	O
Audio	O
released	O
the	O
MaxxBass	O
plug-in	B-Application
to	O
allow	O
computer	O
users	O
to	O
apply	O
the	O
synthesized	O
harmonics	O
to	O
their	O
audio	O
files	O
.	O
</s>
<s>
Later	O
,	O
Waves	O
Audio	O
produced	O
small	O
subwoofers	B-Application
that	O
relied	O
on	O
the	O
missing	B-Application
fundamental	I-Application
concept	O
to	O
give	O
the	O
illusion	O
of	O
low	O
bass	O
.	O
</s>
<s>
The	O
poor	O
bass	O
reproduction	O
of	O
earbuds	B-Device
has	O
been	O
identified	O
as	O
a	O
possible	O
target	O
for	O
such	O
processing	O
.	O
</s>
