<s>
Codec	B-Algorithm
2	I-Algorithm
is	O
a	O
low-bitrate	O
speech	O
audio	O
codec	B-General_Concept
(	O
speech	B-Application
coding	I-Application
)	O
that	O
is	O
patent	O
free	O
and	O
open	B-Application
source	I-Application
.	O
</s>
<s>
Codec	B-Algorithm
2	I-Algorithm
compresses	O
speech	O
using	O
sinusoidal	O
coding	O
,	O
a	O
method	O
specialized	O
for	O
human	O
speech	O
.	O
</s>
<s>
Codec	B-Algorithm
2	I-Algorithm
was	O
designed	O
to	O
be	O
used	O
for	O
amateur	O
radio	O
and	O
other	O
high	O
compression	O
voice	O
applications	O
.	O
</s>
<s>
The	O
codec	B-General_Concept
was	O
developed	O
by	O
David	O
Grant	O
Rowe	O
,	O
with	O
support	O
and	O
cooperation	O
of	O
other	O
researchers	O
(	O
e.g.	O
,	O
Jean-Marc	O
Valin	O
from	O
Opus	B-Algorithm
)	O
.	O
</s>
<s>
Codec	B-Algorithm
2	I-Algorithm
consists	O
of	O
3200	O
,	O
2400	O
,	O
1600	O
,	O
1400	O
,	O
1300	O
,	O
1200	O
,	O
700	O
and	O
450bit/s	O
codec	B-General_Concept
modes	O
.	O
</s>
<s>
It	O
outperforms	O
most	O
other	O
low-bitrate	O
speech	B-Application
codecs	I-Application
.	O
</s>
<s>
For	O
example	O
,	O
it	O
uses	O
half	O
the	O
bandwidth	O
of	O
Advanced	B-Language
Multi-Band	I-Language
Excitation	I-Language
to	O
encode	O
speech	O
with	O
similar	O
quality	O
.	O
</s>
<s>
The	O
speech	B-Application
codec	I-Application
uses	O
16-bit	O
PCM	B-Algorithm
sampled	O
audio	O
,	O
and	O
outputs	O
packed	O
digital	O
bytes	O
.	O
</s>
<s>
When	O
sent	O
packed	O
digital	O
bytes	O
,	O
it	O
outputs	O
PCM	B-Algorithm
sampled	O
audio	O
.	O
</s>
<s>
The	O
reference	O
implementation	O
is	O
open	B-Application
source	I-Application
and	O
is	O
freely	O
available	O
in	O
a	O
GitHub	B-Application
repository	O
.	O
</s>
<s>
The	O
source	O
code	O
is	O
released	O
under	O
the	O
terms	O
of	O
version	O
2.1	O
of	O
the	O
GNU	B-Application
Lesser	I-Application
General	I-Application
Public	I-Application
License	I-Application
(	O
LGPL	B-Application
)	O
.	O
</s>
<s>
It	O
is	O
programmed	O
in	O
C	B-Language
and	O
current	O
source	O
code	O
requires	O
floating-point	B-Algorithm
arithmetic	I-Algorithm
,	O
although	O
the	O
algorithm	O
itself	O
does	O
not	O
require	O
this	O
.	O
</s>
<s>
The	O
reference	O
software	O
package	O
also	O
includes	O
a	O
frequency-division	B-Protocol
multiplex	I-Protocol
digital	O
voice	O
software	O
modem	O
and	O
a	O
graphical	O
user	O
interface	O
based	O
on	O
WxWidgets	B-Language
.	O
</s>
<s>
The	O
software	O
is	O
developed	O
on	O
Linux	B-Application
and	O
a	O
port	O
for	O
Microsoft	B-Application
Windows	I-Application
created	O
with	O
Cygwin	B-Language
is	O
offered	O
in	O
addition	O
to	O
an	O
Apple	O
MacOS	B-Application
version	O
.	O
</s>
<s>
The	O
codec	B-General_Concept
has	O
been	O
presented	O
in	O
various	O
conferences	O
and	O
has	O
received	O
the	O
2012	O
ARRL	O
Technical	O
Innovation	O
Award	O
,	O
and	O
the	O
Linux	B-Application
Australia	O
Conference	O
's	O
Best	O
Presentation	O
Award	O
.	O
</s>
<s>
Internally	O
,	O
parametric	O
audio	O
coding	O
algorithms	O
operate	O
on	O
10ms	O
PCM	B-Algorithm
frames	O
using	O
a	O
model	O
of	O
the	O
human	O
voice	O
.	O
</s>
<s>
Codec	B-Algorithm
2	I-Algorithm
uses	O
sinusoidal	O
coding	O
to	O
model	O
speech	O
,	O
which	O
is	O
closely	O
related	O
to	O
that	O
of	O
multi-band	B-Language
excitation	I-Language
codecs	B-General_Concept
.	O
</s>
<s>
Spoken	O
audio	O
is	O
recreated	O
by	O
modelling	O
speech	O
as	O
a	O
sum	O
of	O
harmonically	O
related	O
sine	O
waves	O
with	O
independent	O
amplitudes	O
called	O
Line	B-Algorithm
spectral	I-Algorithm
pairs	I-Algorithm
,	O
or	O
LSP	O
,	O
on	O
top	O
of	O
a	O
determined	O
fundamental	O
frequency	O
of	O
the	O
speaker	O
's	O
voice	O
(	O
pitch	O
)	O
.	O
</s>
<s>
The	O
LSP	O
coefficients	O
represent	O
the	O
Linear	B-Algorithm
Predictive	I-Algorithm
Coding	I-Algorithm
(	O
LPC	O
)	O
model	O
in	O
the	O
frequency	O
domain	O
,	O
and	O
lend	O
themselves	O
to	O
a	O
robust	O
and	O
efficient	O
quantisation	O
of	O
the	O
LPC	O
parameters	O
.	O
</s>
<s>
Codec2	B-Algorithm
has	O
also	O
been	O
integrated	O
into	O
FreeSWITCH	B-Language
and	O
there	O
's	O
a	O
patch	O
available	O
for	O
support	O
in	O
Asterisk	B-Language
.	O
</s>
<s>
There	O
was	O
an	O
FM-to-Codec2	O
digital	O
voice	O
repeater	O
in	O
earth	O
orbit	O
on	O
amateur	O
radio	O
CubeSat	O
LilacSat-1	O
(	O
call	O
sign	O
ON02CN	O
,	O
QB50	O
constellation	O
)	O
,	O
which	O
was	O
launched	O
and	O
subsequently	O
deployed	O
from	O
the	O
International	O
Space	O
Station	O
in	O
2017	O
.	O
</s>
<s>
The	O
prominent	O
free	B-Application
software	I-Application
advocate	O
and	O
radio	O
amateur	O
Bruce	O
Perens	O
lobbied	O
for	O
the	O
creation	O
of	O
a	O
free	O
speech	B-Application
codec	I-Application
for	O
operation	O
at	O
less	O
than	O
5kBit/s	O
.	O
</s>
<s>
Since	O
he	O
did	O
not	O
have	O
the	O
background	O
himself	O
,	O
he	O
approached	O
Jean-Marc	O
Valin	O
in	O
2008	O
,	O
who	O
introduced	O
him	O
to	O
lead	O
developer	O
David	O
Grant	O
Rowe	O
,	O
who	O
has	O
worked	O
with	O
Valin	O
on	O
Speex	B-Application
on	O
several	O
occasions	O
.	O
</s>
<s>
Rowe	O
himself	O
was	O
also	O
a	O
radio	O
amateur	O
(	O
amateur	O
radio	O
call	O
sign	O
VK5DGR	O
)	O
and	O
had	O
experience	O
in	O
creating	O
and	O
using	O
voice	B-Application
codecs	I-Application
and	O
other	O
signal	O
processing	O
algorithms	O
for	O
speech	O
signals	O
.	O
</s>
<s>
He	O
obtained	O
a	O
PhD	O
in	O
speech	B-Application
coding	I-Application
in	O
the	O
1990s	O
and	O
was	O
involved	O
in	O
the	O
development	O
of	O
one	O
of	O
the	O
first	O
satellite	O
telephony	O
systems	O
(	O
Mobilesat	O
)	O
.	O
</s>
<s>
In	O
January	O
2012	O
,	O
at	O
linux.conf.au,	O
Jean-Marc	O
Valin	O
helped	O
improve	O
the	O
quantization	O
of	O
line	B-Algorithm
spectral	I-Algorithm
pairs	I-Algorithm
,	O
which	O
Rowe	O
is	O
less	O
familiar	O
with	O
.	O
</s>
<s>
Codec	B-Algorithm
2	I-Algorithm
700C	O
,	O
a	O
new	O
mode	O
with	O
a	O
bit	O
rate	O
of	O
700bit/s	O
,	O
was	O
finished	O
in	O
early	O
2017	O
.	O
</s>
