<s>
Active	B-Application
sound	I-Application
design	I-Application
is	O
an	O
acoustic	O
technology	O
concept	O
used	O
in	O
automotive	O
vehicles	O
to	O
alter	O
or	O
enhance	O
the	O
sound	O
inside	O
and	O
outside	O
of	O
the	O
vehicle	O
.	O
</s>
<s>
Active	B-Application
sound	I-Application
design	I-Application
(	O
ASD	O
)	O
often	O
uses	O
active	O
noise	O
control	O
and	O
acoustic	O
enhancement	O
techniques	O
to	O
achieve	O
a	O
synthesized	O
vehicle	O
sound	O
.	O
</s>
<s>
Engine	B-Application
sound	I-Application
enhancement	I-Application
(	O
ESE	O
)	O
is	O
a	O
technology	O
that	O
allows	O
manufacturers	O
to	O
enhance	O
engine	O
sounds	O
with	O
synthetic	O
noise	O
composed	O
from	O
live	O
engine	O
data	O
,	O
including	O
components	O
such	O
as	O
engine	O
revolutions	O
per	O
minute	O
(	O
RPM	O
)	O
and	O
engine	O
torque	B-General_Concept
.	O
</s>
<s>
Electric	O
and	O
hybrid	O
vehicles	O
lack	O
a	O
distinct	O
engine	O
sound	O
altogether	O
,	O
instead	O
featuring	O
a	O
quieter	O
high	B-Algorithm
frequency	I-Algorithm
noise	O
that	O
causes	O
annoyance	O
for	O
vehicle	O
passengers	O
and	O
poses	O
a	O
threat	O
to	O
pedestrians	O
who	O
may	O
not	O
recognize	O
an	O
oncoming	O
vehicle	O
.	O
</s>
<s>
Active	B-Application
sound	I-Application
design	I-Application
(	O
ASD	O
)	O
takes	O
inputs	B-General_Concept
from	O
engine	O
and	O
vehicle	O
speed	O
,	O
pedal	O
input	O
,	O
exhaust	O
noise	O
,	O
and	O
vehicle	O
vibrations	O
to	O
change	O
the	O
interior	O
and	O
exterior	O
noise	O
of	O
the	O
vehicle	O
.	O
</s>
<s>
These	O
input	O
variables	O
are	O
filtered	O
to	O
produce	O
desired	O
outputs	B-General_Concept
.	O
</s>
<s>
Active	O
mounts	O
:	O
taking	O
inputs	B-General_Concept
from	O
the	O
exterior	O
vehicle	O
and	O
feeding	O
vibration	O
outputs	B-General_Concept
to	O
the	O
vehicle	O
interior	O
.	O
</s>
<s>
These	O
cylinders	O
fire	O
periodically	O
and	O
can	O
be	O
reduced	O
to	O
a	O
series	O
of	O
sinusoidal	O
waves	O
(	O
by	O
conventions	O
of	O
the	O
Fourier	B-Algorithm
transform	I-Algorithm
)	O
.	O
</s>
<s>
These	O
sine	O
waves	O
are	O
dictated	O
by	O
the	O
rotations	O
per	O
minute	O
(	O
RPM	O
)	O
of	O
the	O
engine	O
crankshaft	B-Language
and	O
the	O
firing	O
order	O
,	O
or	O
arrangement	O
,	O
of	O
the	O
cylinders	O
.	O
</s>
<s>
To	O
enrich	O
engine	O
sound	O
in	O
the	O
passenger	O
cabin	O
,	O
the	O
harmonic	O
orders	O
of	O
engine	O
sound	O
missing	O
from	O
the	O
interior	O
sound	O
can	O
be	O
amplified	O
through	O
Digital	B-General_Concept
Signal	I-General_Concept
Processing	I-General_Concept
(	O
DSP	O
)	O
techniques	O
.	O
</s>
<s>
To	O
capture	O
the	O
missing	O
orders	O
,	O
the	O
engine	O
load	O
condition	O
is	O
identified	O
by	O
acceleration	O
sensors	O
on	O
the	O
engine	O
of	O
older	O
vehicles	O
,	O
or	O
by	O
way	O
of	O
the	O
Controller	B-Protocol
Area	I-Protocol
Network	I-Protocol
bus	I-Protocol
(	O
CAN-bus	B-Protocol
)	O
in	O
modern	O
cars	O
.	O
</s>
<s>
To	O
minimize	O
artefacts	O
(	O
disruptive	O
clicks	O
)	O
during	O
the	O
transfer	O
,	O
the	O
signal	O
is	O
passed	O
through	O
cascading	O
high	O
-	O
and	O
low-pass	B-Algorithm
filters	I-Algorithm
.	O
</s>
<s>
Based	O
on	O
studies	O
of	O
user	O
preference	O
in	O
vehicle	O
interiors	O
,	O
manufacturers	O
aim	O
to	O
reduce	O
loudness	B-Algorithm
increment	O
and	O
high-frequency	B-Algorithm
sound	O
for	O
a	O
more	O
pleasant	O
driving	O
experience	O
.	O
</s>
<s>
In	O
modern	O
EVs	O
,	O
the	O
stock	O
vehicle	O
noise	O
is	O
masked	O
with	O
an	O
RPM-dependent	O
low-pass-filtered	O
sound	O
.	O
</s>
<s>
This	O
low-pass-filtered	O
sound	O
is	O
a	O
lower-frequency	O
synthetic	O
sound	O
that	O
is	O
based	O
on	O
the	O
EV	O
’s	O
actual	O
engine	O
parameters	O
,	O
like	O
speed	O
and	O
load	O
.	O
</s>
<s>
Subharmonics	O
(	O
lower-frequency	O
copies	O
)	O
are	O
then	O
isolated	O
from	O
the	O
original	O
high-frequency	B-Algorithm
components	O
of	O
the	O
EV	O
.	O
</s>
<s>
Current	O
implementations	O
of	O
active	B-Application
sound	I-Application
design	I-Application
in	O
combustion	O
engine	O
vehicles	O
may	O
not	O
accurately	O
reproduce	O
the	O
micro	O
structure	O
variations	O
(	O
variations	O
between	O
cylinder	O
firings	O
)	O
of	O
the	O
combustion	O
process	O
.	O
</s>
<s>
In	O
vehicle	O
models	O
such	O
as	O
the	O
BMW	O
M5	O
,	O
an	O
engine	B-Device
management	I-Device
system	I-Device
enhances	O
the	O
sounds	O
provided	O
by	O
speed	O
and	O
engine	O
power	O
by	O
filtering	O
through	O
the	O
audio	O
data	O
it	O
receives	O
.	O
</s>
<s>
Similarly	O
,	O
the	O
Kia	O
Stinger	O
features	O
five	O
drive	O
modes	O
(	O
eco	O
,	O
comfort	O
,	O
smart	O
,	O
sport	O
,	O
and	O
custom	O
)	O
that	O
adjust	O
the	O
loudness	B-Algorithm
and	O
aggressiveness	O
of	O
the	O
sound	O
inside	O
the	O
vehicle	O
cabin	O
.	O
</s>
<s>
The	O
Helmholtz	O
universal	O
resonator	O
restricts	O
engine	O
sound	O
through	O
an	O
electronically	O
controlled	O
valve	O
that	O
oscillates	B-Algorithm
with	O
air	O
,	O
much	O
like	O
the	O
sound	O
that	O
is	O
emitted	O
when	O
one	O
blows	O
over	O
the	O
top	O
of	O
a	O
bottle	O
.	O
</s>
