<s>
Advanced	B-Application
Linux	I-Application
Sound	I-Application
Architecture	I-Application
(	O
ALSA	B-Application
)	O
is	O
a	O
software	B-Architecture
framework	I-Architecture
and	O
part	O
of	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
that	O
provides	O
an	O
application	B-Application
programming	I-Application
interface	I-Application
(	O
API	B-Application
)	O
for	O
sound	B-Device
card	I-Device
device	B-Application
drivers	I-Application
.	O
</s>
<s>
Some	O
of	O
the	O
goals	O
of	O
the	O
ALSA	B-Application
project	O
at	O
its	O
inception	O
were	O
automatic	O
configuration	O
of	O
sound-card	B-Device
hardware	O
and	O
graceful	O
handling	O
of	O
multiple	O
sound	O
devices	O
in	O
a	O
system	O
.	O
</s>
<s>
ALSA	B-Application
is	O
released	O
under	O
GPL-2.0-or-later	B-License
and	O
LGPL-2.1-or-later	B-Application
.	O
</s>
<s>
On	O
Linux	B-Operating_System
,	O
sound	O
servers	O
,	O
like	O
sndio	B-Application
,	O
PulseAudio	B-Library
,	O
JACK	B-Application
(	O
low-latency	O
professional-grade	O
audio	O
editing	O
and	O
mixing	O
)	O
and	O
PipeWire	B-Application
,	O
and	O
higher-level	O
APIs	B-Application
(	O
e.g	O
OpenAL	B-Application
,	O
SDL	B-Operating_System
audio	O
,	O
etc	O
.	O
)	O
</s>
<s>
work	O
on	O
top	O
of	O
ALSA	B-Application
and	O
its	O
sound	B-Device
card	I-Device
device	B-Application
drivers	I-Application
.	O
</s>
<s>
ALSA	B-Application
succeeded	O
the	O
older	O
Linux	B-Operating_System
port	O
of	O
the	O
Open	B-Library
Sound	I-Library
System	I-Library
(	O
OSS	O
)	O
.	O
</s>
<s>
The	O
project	O
to	O
develop	O
ALSA	B-Application
was	O
led	O
by	O
Jaroslav	B-Application
Kysela	I-Application
,	O
and	O
was	O
based	O
on	O
the	O
Linux	B-Application
device	I-Application
driver	I-Application
for	O
the	O
Gravis	B-Application
Ultrasound	I-Application
sound	B-Device
card	I-Device
.	O
</s>
<s>
It	O
started	O
in	O
1998	O
and	O
was	O
developed	O
separately	O
from	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
until	O
it	O
was	O
introduced	O
in	O
the	O
2.5	O
development	O
series	O
in	O
2002	O
(	O
2.5.4	O
–	O
2.5.5	O
)	O
.	O
</s>
<s>
In	O
the	O
2.6	O
version	O
,	O
it	O
replaced	O
the	O
previous	O
system	O
,	O
Open	B-Library
Sound	I-Library
System	I-Library
(	O
OSS	O
)	O
,	O
by	O
default	O
(	O
although	O
a	O
backwards-compatibility	O
layer	O
does	O
exist	O
)	O
.	O
</s>
<s>
ALSA	B-Application
has	O
a	O
larger	O
and	O
more	O
complex	O
API	B-Application
than	O
OSS	O
,	O
so	O
it	O
can	O
be	O
more	O
difficult	O
to	O
develop	O
an	O
application	O
that	O
uses	O
ALSA	B-Application
as	O
its	O
sound	O
technology	O
.	O
</s>
<s>
While	O
ALSA	B-Application
may	O
be	O
configured	O
to	O
provide	O
an	O
OSS	O
emulation	O
layer	O
,	O
such	O
functionality	O
is	O
no	O
longer	O
available	O
or	O
is	O
not	O
installed	O
by	O
default	O
in	O
many	O
Linux	B-Operating_System
distributions	O
.	O
</s>
<s>
ALSA	B-Application
was	O
designed	O
with	O
some	O
features	O
which	O
were	O
not	O
,	O
at	O
the	O
time	O
of	O
its	O
conception	O
,	O
supported	O
by	O
OSS	O
:	O
</s>
<s>
Hardware	B-General_Concept
mixing	I-General_Concept
of	O
multiple	O
channels	O
.	O
</s>
<s>
Multiprocessor-friendly	O
,	O
thread-safe	B-Operating_System
device	B-Application
drivers	I-Application
.	O
</s>
<s>
Besides	O
the	O
sound	O
device	B-Application
drivers	I-Application
,	O
ALSA	B-Application
bundles	O
a	O
user-space	B-Operating_System
library	B-Library
for	O
application	O
developers	O
who	O
want	O
to	O
use	O
driver	O
features	O
through	O
an	O
interface	O
that	O
is	O
higher-level	O
than	O
the	O
interface	O
provided	O
for	O
direct	O
interaction	O
with	O
the	O
kernel	B-Application
drivers	I-Application
.	O
</s>
<s>
Unlike	O
the	O
kernel	B-Operating_System
API	B-Application
,	O
which	O
tries	O
to	O
reflect	O
the	O
capabilities	O
of	O
the	O
hardware	O
directly	O
,	O
ALSA	B-Application
's	O
user-space	B-Operating_System
library	B-Library
presents	O
an	O
abstraction	O
that	O
remains	O
as	O
standardized	O
as	O
possible	O
across	O
disparate	O
underlying	O
hardware	O
elements	O
.	O
</s>
<s>
This	O
goal	O
is	O
achieved	O
in	O
part	O
by	O
using	O
software	B-Application
plug-ins	I-Application
;	O
for	O
example	O
,	O
many	O
modern	O
sound	B-Device
cards	I-Device
or	O
built-in	O
sound	O
chips	O
do	O
not	O
have	O
a	O
"	O
master	O
volume	O
"	O
control	O
.	O
</s>
<s>
Instead	O
,	O
for	O
these	O
devices	O
,	O
the	O
user	B-Operating_System
space	I-Operating_System
library	B-Library
provides	O
a	O
software	O
volume	O
control	O
using	O
the	O
"	O
softvol	B-Application
"	O
plug-in	B-Application
,	O
and	O
ordinary	O
application	O
software	O
need	O
not	O
care	O
whether	O
such	O
a	O
control	O
is	O
implemented	O
by	O
underlying	O
hardware	O
or	O
software	O
emulation	O
of	O
such	O
underlying	O
hardware	O
.	O
</s>
<s>
Additional	O
to	O
the	O
software	B-Architecture
framework	I-Architecture
internal	O
to	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
,	O
the	O
ALSA	B-Application
project	O
also	O
provides	O
the	O
command-line	O
tools	O
and	O
utilities	O
alsactl	O
,	O
amixer	O
,	O
arecord/aplay	O
and	O
alsamixer	B-Device
,	O
an	O
ncurses-based	O
TUI	B-Application
.	O
</s>
<s>
There	O
also	O
are	O
GUIs	O
programmed	O
by	O
third-party	O
developers	O
,	O
such	O
as	O
GNOME-ALSAmixer	O
(	O
using	O
GTK	B-Application
)	O
,	O
Kmix	O
,	O
XFCE4-mixer	O
,	O
LXpanel	O
,	O
QasHctl	O
,	O
QasMixer	O
,	O
Pavucontrol	O
,	O
AconnectGUI	O
,	O
tapiir	O
,	O
polarbear	O
,	O
ALSAmixerGUI	O
(	O
using	O
FLTK	B-Language
)	O
,	O
ZynAddSubFX	B-Language
,	O
Yoshimi	B-Application
,	O
and	O
even	O
more	O
.	O
</s>
<s>
This	O
section	O
provides	O
an	O
overview	O
of	O
basic	O
concepts	O
pertaining	O
to	O
ALSA	B-Application
.	O
</s>
<s>
Typically	O
,	O
ALSA	B-Application
supports	O
up	O
to	O
eight	O
cards	O
,	O
numbered	O
0	O
through	O
7	O
;	O
each	O
card	O
is	O
a	O
physical	O
or	O
logical	O
kernel	B-Operating_System
device	O
capable	O
of	O
input	O
and	O
output	O
.	O
</s>
<s>
A	O
card	O
's	O
interface	O
is	O
a	O
description	O
of	O
an	O
ALSA	B-Application
protocol	O
for	O
accessing	O
the	O
card	O
;	O
possible	O
interfaces	O
include	O
:	O
hw	O
,	O
plughw	O
,	O
default	O
,	O
and	O
plug:dmix	O
.	O
</s>
<s>
The	O
hw	O
interface	O
provides	O
direct	O
access	O
to	O
the	O
kernel	B-Operating_System
device	O
,	O
but	O
no	O
software	O
mixing	O
or	O
stream	O
adaptation	O
support	O
.	O
</s>
<s>
An	O
ALSA	B-Application
stream	O
is	O
a	O
data	O
flow	O
representing	O
sound	O
;	O
the	O
most	O
common	O
stream	O
format	O
is	O
PCM	B-Algorithm
that	O
must	O
be	O
produced	O
in	O
such	O
a	O
way	O
as	O
to	O
match	O
the	O
characteristics	O
or	O
parameters	O
of	O
the	O
hardware	O
,	O
including	O
:	O
</s>
<s>
The	O
ALSA	B-Application
System	B-Architecture
on	I-Architecture
Chip	I-Architecture
(	O
ASoC	B-Application
)	O
layer	O
aims	O
to	O
provide	O
better	O
support	O
for	O
ALSA	B-Application
on	O
embedded	B-Architecture
systems	I-Architecture
that	O
use	O
a	O
system-on-chip	B-Architecture
(	O
SoC	O
)	O
design	O
.	O
</s>
<s>
Open	B-Library
Sound	I-Library
System	I-Library
version	O
4	O
is	O
able	O
to	O
emulate	O
ALSA	B-Application
.	O
</s>
<s>
QNX	B-Operating_System
uses	O
a	O
sound	O
system	O
derived	O
from	O
,	O
but	O
not	O
directly	O
compatible	O
with	O
,	O
ALSA	B-Application
.	O
</s>
<s>
The	O
header	O
file	O
and	O
library	B-Library
names	O
are	O
still	O
"	O
asound	O
"	O
,	O
same	O
as	O
the	O
ALSA	B-Application
names	O
.	O
</s>
<s>
ALSA	B-Application
API	B-Application
uses	O
calls	O
in	O
a	O
way	O
not	O
allowed	O
in	O
the	O
QNX	B-Operating_System
kernel	I-Operating_System
.	O
</s>
