<s>
Mixed-excitation	B-Algorithm
linear	I-Algorithm
prediction	I-Algorithm
(	O
MELP	B-Algorithm
)	O
is	O
a	O
United	O
States	O
Department	O
of	O
Defense	O
speech	B-Application
coding	I-Application
standard	O
used	O
mainly	O
in	O
military	O
applications	O
and	O
satellite	B-Application
communications	O
,	O
secure	O
voice	O
,	O
and	O
secure	O
radio	O
devices	O
.	O
</s>
<s>
The	O
current	O
"	O
enhanced	O
"	O
version	O
is	O
known	O
as	O
MELPe	B-Algorithm
.	O
</s>
<s>
The	O
initial	O
MELP	B-Algorithm
was	O
invented	O
by	O
Alan	O
McCree	O
around	O
1995	O
while	O
a	O
graduate	O
student	O
at	O
the	O
Center	O
for	O
Signal	O
and	O
Image	O
Processing	O
(	O
CSIP	O
)	O
at	O
Georgia	O
Tech	O
,	O
and	O
the	O
original	O
MELP	B-Algorithm
related	O
patents	O
have	O
expired	O
by	O
now	O
.	O
</s>
<s>
That	O
initial	O
speech	B-Application
coder	I-Application
was	O
standardized	O
in	O
1997	O
and	O
was	O
known	O
as	O
MIL-STD-3005	O
.	O
</s>
<s>
It	O
surpassed	O
other	O
candidate	O
vocoders	B-Application
in	O
the	O
US	O
DoD	O
competition	O
,	O
including	O
:	O
(	O
a	O
)	O
Frequency	O
Selective	O
Harmonic	O
Coder	O
(	O
FSHC	O
)	O
,	O
(	O
b	O
)	O
Advanced	B-Language
Multi-Band	I-Language
Excitation	I-Language
(	O
AMBE	O
)	O
,	O
(	O
c	O
)	O
Enhanced	O
Multiband	O
Excitation	O
(	O
EMBE	O
)	O
,	O
(	O
d	O
)	O
Sinusoid	O
Transform	O
Coder	O
(	O
STC	O
)	O
,	O
and	O
(	O
e	O
)	O
Subband	O
LPC	O
Coder	O
(	O
SBC	O
)	O
.	O
</s>
<s>
Due	O
to	O
its	O
lower	O
complexity	O
than	O
Waveform	O
Interpolative	O
(	O
WI	O
)	O
coder	O
,	O
the	O
MELP	B-Algorithm
vocoder	B-Application
won	O
the	O
DoD	O
competition	O
and	O
was	O
selected	O
for	O
MIL-STD-3005	O
.	O
</s>
<s>
Between	O
1998	O
and	O
2001	O
,	O
a	O
new	O
MELP-based	O
vocoder	B-Application
was	O
created	O
at	O
half	O
the	O
rate	O
(	O
i.e.	O
</s>
<s>
1200	O
bit/s	O
)	O
,	O
and	O
substantial	O
enhancements	O
were	O
added	O
to	O
the	O
MIL-STD-3005	O
by	O
SignalCom	O
(	O
later	O
acquired	O
by	O
Microsoft	O
)	O
,	O
Compandent	O
,	O
and	O
AT&T	O
Corporation	O
,	O
which	O
included	O
(	O
a	O
)	O
additional	O
new	O
vocoder	B-Application
at	O
half	O
the	O
rate	O
(	O
i.e.	O
</s>
<s>
This	O
fairly	O
significant	O
development	O
was	O
aimed	O
to	O
create	O
a	O
new	O
coder	O
at	O
half	O
the	O
rate	O
and	O
have	O
it	O
interoperable	O
with	O
the	O
old	O
MELP	B-Algorithm
standard	O
.	O
</s>
<s>
This	O
enhanced-MELP	O
(	O
also	O
known	O
as	O
MELPe	B-Algorithm
)	O
was	O
adopted	O
as	O
the	O
new	O
MIL-STD-3005	O
in	O
2001	O
in	O
form	O
of	O
annexes	O
and	O
supplements	O
made	O
to	O
the	O
original	O
MIL-STD-3005	O
,	O
enabling	O
the	O
same	O
quality	O
as	O
the	O
old	O
2400	O
bit/s	O
MELP	B-Algorithm
's	O
at	O
half	O
the	O
rate	O
.	O
</s>
<s>
One	O
of	O
the	O
greatest	O
advantages	O
of	O
the	O
new	O
2400	O
bit/s	O
MELPe	B-Algorithm
is	O
that	O
it	O
shares	O
the	O
same	O
bit	O
format	O
as	O
MELP	B-Algorithm
,	O
and	O
hence	O
can	O
interoperate	O
with	O
legacy	O
MELP	B-Algorithm
systems	O
,	O
but	O
would	O
deliver	O
better	O
quality	O
at	O
both	O
ends	O
.	O
</s>
<s>
MELPe	B-Algorithm
provides	O
much	O
better	O
quality	O
than	O
all	O
older	O
military	O
standards	O
,	O
especially	O
in	O
noisy	O
environments	O
such	O
as	O
battlefield	O
and	O
vehicles	O
and	O
aircraft	O
.	O
</s>
<s>
In	O
2002	O
,	O
following	O
extensive	O
competition	O
and	O
testing	O
,	O
the	O
2400	O
and	O
1200	O
bit/s	O
US	O
DoD	O
MELPe	B-Algorithm
was	O
adopted	O
also	O
as	O
NATO	O
standard	O
,	O
known	O
as	O
STANAG-4591	O
.	O
</s>
<s>
The	O
NATO	O
testing	O
performance	O
measurements	O
included	O
voice	O
intelligibility	O
,	O
voice	O
quality	O
,	O
speaker	O
recognition	O
,	O
language	O
dependency	O
,	O
speaker	O
dependency	O
,	O
10	O
acoustic	O
noise	O
environments	O
,	O
transmission	O
channel	O
under	O
1%	O
BER	O
,	O
tandem	O
using	O
16	O
kbps	O
CVSD	B-Algorithm
vocoder	B-Application
,	O
whispered	O
speech	O
,	O
and	O
real-time	O
implementation	O
.	O
</s>
<s>
As	O
part	O
of	O
NATO	O
testing	O
for	O
new	O
NATO	O
standard	O
,	O
MELPe	B-Algorithm
was	O
tested	O
against	O
other	O
candidates	O
such	O
as	O
France	O
's	O
HSX	O
(	O
Harmonic	O
Stochastic	O
eXcitation	O
)	O
and	O
Turkey	O
's	O
SB-LPC	O
(	O
Split-Band	O
Linear	O
Predictive	O
Coding	O
)	O
,	O
as	O
well	O
as	O
the	O
old	O
secure	O
voice	O
standards	O
such	O
as	O
FS1015	O
LPC-10e	O
(	O
2.4	O
kbit/s	O
)	O
,	O
FS1016	B-Algorithm
CELP	B-Algorithm
(	O
4.8	O
kbit/s	O
)	O
and	O
CVSD	B-Algorithm
(	O
16	O
kbit/s	O
)	O
.	O
</s>
<s>
Subsequently	O
,	O
the	O
MELPe	B-Algorithm
won	O
also	O
the	O
NATO	O
competition	O
,	O
surpassing	O
the	O
quality	O
of	O
all	O
other	O
candidates	O
as	O
well	O
as	O
the	O
quality	O
of	O
all	O
old	O
secure	O
voice	O
standards	O
(	O
CVSD	B-Algorithm
,	O
CELP	B-Algorithm
and	O
LPC-10e	O
)	O
.	O
</s>
<s>
The	O
NATO	O
competition	O
concluded	O
that	O
MELPe	B-Algorithm
substantially	O
improved	O
performance	O
(	O
in	O
terms	O
of	O
speech	O
quality	O
,	O
intelligibility	O
,	O
and	O
noise	O
immunity	O
)	O
,	O
while	O
reducing	O
throughput	O
requirements	O
.	O
</s>
<s>
Compandent	O
Inc	O
,	O
as	O
a	O
part	O
of	O
MELPe-based	O
projects	O
performed	O
for	O
NSA	O
and	O
NATO	O
,	O
provided	O
NSA	O
and	O
NATO	O
with	O
special	O
test-bed	O
platform	O
known	O
as	O
MELCODER	O
device	O
that	O
provided	O
the	O
golden	O
reference	O
for	O
real-time	O
implementation	O
of	O
MELPe	B-Algorithm
.	O
</s>
<s>
The	O
low-cost	O
FLEXI-232	O
Data	O
Terminal	O
Equipment	O
(	O
DTE	O
)	O
made	O
by	O
Compandent	O
,	O
which	O
are	O
based	O
on	O
the	O
MELCODER	O
golden	O
reference	O
,	O
are	O
very	O
popular	O
and	O
widely	O
used	O
for	O
evaluating	O
and	O
testing	O
MELPe	B-Algorithm
in	O
real-time	O
,	O
various	O
channels	O
&	O
networks	O
,	O
and	O
field	O
conditions	O
.	O
</s>
<s>
In	O
2005	O
,	O
a	O
new	O
600	O
bit/s	O
rate	O
MELPe	B-Algorithm
variation	O
by	O
Thales	O
Group	O
(	O
France	O
)	O
was	O
added	O
(	O
without	O
extensive	O
competition	O
and	O
testing	O
as	O
performed	O
for	O
the	O
2400/1200	O
bit/s	O
MELPe	B-Algorithm
)	O
to	O
the	O
NATO	O
standard	O
STANAG-4591	O
.	O
</s>
<s>
In	O
2010	O
,	O
MIT	O
Lincoln	O
Labs	O
,	O
Compandent	O
,	O
BBN	O
,	O
and	O
General	O
Dynamics	O
also	O
developed	O
for	O
DARPA	O
a	O
300	O
bit/s	O
MELP	B-Algorithm
device	O
.	O
</s>
<s>
Its	O
quality	O
was	O
better	O
than	O
the	O
600	O
bit/s	O
MELPe	B-Algorithm
,	O
but	O
its	O
algorithmic	O
delay	O
was	O
longer	O
.	O
</s>
<s>
The	O
MELPe	B-Algorithm
has	O
been	O
implemented	O
in	O
many	O
applications	O
including	O
secure	O
radio	O
devices	O
,	O
satellite	B-Application
communications	O
,	O
VoIP	O
,	O
and	O
cellphone	O
applications	O
.	O
</s>
<s>
Such	O
expertise	O
requires	O
the	O
understanding	O
of	O
the	O
MELPe	B-Algorithm
's	O
bits	O
sensitivity	O
to	O
errors	O
.	O
</s>
<s>
The	O
2400	O
bit/s	O
and	O
1200	O
bit/s	O
MELPe	B-Algorithm
include	O
synchronization	O
bit	O
,	O
which	O
is	O
useful	O
in	O
serial	O
communications	O
.	O
</s>
<s>
MELPe	B-Algorithm
is	O
intended	O
for	O
the	O
compression	O
of	O
speech	O
.	O
</s>
<s>
Given	O
an	O
audio	O
input	O
sampled	O
at	O
8kHz	O
,	O
the	O
MELPe	B-Algorithm
codec	O
yields	O
the	O
following	O
compression	O
ratios	O
over	O
a	O
64	O
kbit/s	O
μ-Law	O
G.711	O
datastream	O
,	O
discounting	O
the	O
effects	O
of	O
protocol	O
overhead	O
:	O
</s>
<s>
Generally	O
,	O
speech	B-Application
coding	I-Application
involves	O
a	O
trade-off	O
of	O
different	O
aspects	O
including	O
bit-rate	O
,	O
speech	O
quality	O
,	O
delay	O
(	O
frame	O
size	O
and	O
lookahead	O
)	O
,	O
computational	O
complexity	O
,	O
robustness	O
to	O
different	O
speakers	O
and	O
languages	O
,	O
robustness	O
to	O
different	O
background	O
noises	O
,	O
channel	O
error	O
robustness	O
,	O
and	O
also	O
codec	O
state	O
recovery	O
in	O
the	O
face	O
of	O
packet	O
loss	O
.	O
</s>
<s>
Since	O
the	O
MELPe	B-Algorithm
's	O
lower	O
rates	O
(	O
600	O
and	O
1200	O
bit/s	O
)	O
are	O
supersets	O
of	O
the	O
2400	O
bit/s	O
rate	O
,	O
the	O
algorithm	O
complexity	O
(	O
e.g.	O
</s>
<s>
MELPe	B-Algorithm
(	O
and/or	O
its	O
derivatives	O
)	O
is	O
subject	O
to	O
IPR	O
licensing	O
from	O
the	O
following	O
companies	O
,	O
Texas	O
Instruments	O
(	O
2400	O
bit/s	O
MELP	B-Algorithm
algorithm	O
/	O
source	O
code	O
)	O
,	O
Microsoft	O
(	O
1200	O
bit/s	O
transcoder	O
)	O
,	O
Thales	O
Group	O
(	O
600	O
bit/s	O
rate	O
)	O
,	O
Compandent	O
,	O
and	O
AT&T	O
(	O
Noise	O
Pre-Processor	O
NPP	O
)	O
.	O
</s>
