jackd
JACK Audio Connection Kit sound server
Synopsis
jackd
[options] -d backend
[backend-parameters]
jackd --help
add an example, a script, a trick and tips
examples
Print usage message for the parameters specific to each backend.
jackd -d alsa --help
jackd -d coreaudio --help
jackd -d net --help
jackd -d dummy --help
jackd -d firewire --help
jackd -d freebob --help
jackd -d oss --help
jackd -d sun --help
jackd -d portaudio --help
Run the JACK daemon with realtime priority using the first ALSA
hardware card defined in /etc/modules.conf.
jackstart --realtime --driver=alsa
Run the JACK daemon with low latency giving verbose output, which
can be helpful for trouble-shooting system latency problems. A
reasonably well-tuned system with a good sound card and a
low-latency kernel can handle these values reliably. Some can do
better. If you get xrun messages, try a larger buffer. Tuning a
system for low latency can be challenging. The JACK FAQ,
http://jackit.sourceforge.net/docs/faq.php has some useful
suggestions.
jackstart -Rv -d alsa -p 128 -n 2 -r 44100
Run jackd with realtime priority using the "sblive" ALSA
device defined in ~/.asoundrc. Apply shaped dithering to playback
audio.
jackd -R -d alsa -d sblive --dither=shaped
Run jackd with no special privileges using the second ALSA
hardware card defined in /etc/modules.conf. Any xruns
reported by the ALSA backend will be ignored. The larger buffer
helps reduce data loss. Rectangular dithering will be used for
playback.
jackd -d alsa -d hw:1 -p2048 -n3 --softmode -zr
Run jackd in full-duplex mode using the ALSA hw:0,0 device
for playback and the hw:0,2 device for capture.
jackd -d alsa -P hw:0,0 -C hw:0,2
Run jackd in playback-only mode using the ALSA hw:0,0
device.
jackd -d alsa -P hw:0,0
source
jackd -r -d alsa -r 44100
source
killall pulseaudio
killall pulseaudio
jackd -R -d alsa -r 44100
source
alias j="jackd -r -d alsa -r 44100"
source
Simulating audio playback on headless linux server
Have you tried the snd-dummy module?
$ modinfo snd-dummy
filename: /lib/modules/2.6.28-11-generic/kernel/sound/drivers/snd-dummy.ko
license: GPL
description: Dummy soundcard (/dev/null)
author: Jaroslav Kysela <perex@perex.cz>
srcversion: AFF1C8B79BA4E7C29AE9874
depends: snd-pcm,snd
vermagic: 2.6.28-11-generic SMP mod_unload modversions 586
parm: index:Index value for dummy soundcard. (array of int)
parm: id:ID string for dummy soundcard. (array of charp)
parm: enable:Enable this dummy soundcard. (array of bool)
parm: pcm_devs:PCM devices # (0-4) for dummy driver. (array of int)
parm: pcm_substreams:PCM substreams # (1-16) for dummy driver. (array of int)
source
Using sox low pass filter with jack
SoX doesn’t have a JACK driver. It wouldn’t be too difficult to
write one, but due to the architecture of SoX, the latency would
always be higher than strictly necessary.
If all you need is simple IIR filtering, just use a LADSPA host
such as JACK Rack and suitable plugins, such as those by
Matthias Nagorni or
buttlow_iir/butthigh_iir etc. from
Steve Harris’s
collection.
description
jackd is
the JACK audio server daemon, a low-latency audio
server. Originally written for the GNU/Linux operating
system, it also supports Mac OS X and various Unix
platforms. JACK can connect a number of different client
applications to an audio device and also to each other. Most
clients are external, running in their own processes as
normal applications. JACK also supports internal clients,
which run within the jackd process using a loadable
"plugin" interface.
JACK differs
from other audio servers in being designed from the ground
up for professional audio work. It focuses on two key areas:
synchronous execution of all clients, and low latency
operation.
For the latest
JACK information, please consult the web site,
<http://www.jackaudio.org>.
options
-d,
--driver backend
[backend-parameters ]
Select the audio interface
backend. The current list of supported backends is:
alsa, coreaudio, dummy, freebob,
oss sun and portaudio. They are not all
available on all platforms. All
backend-parameters are optional.
-h,
--help
Print a brief usage message
describing the main jackd options. These do not
include backend-parameters, which are listed
using the --help option for each specific
backend. Examples below show how to list them.
-m,
--no-mlock
Do not attempt to lock memory,
even if --realtime.
-n,
--name server-name
Name this jackd instance
server-name. If unspecified, this name comes
from the $JACK_DEFAULT_SERVER environment variable.
It will be "default" if that is not defined.
-p,
--port-max n
Set the maximum number of ports
the JACK server can manage. The default value is 256.
--replace-registry
Remove the shared memory
registry used by all JACK server instances before startup.
This should rarely be used, and is intended only for
occasions when the structure of this registry changes in
ways that are incompatible across JACK versions (which is
rare).
-R,
--realtime
Use realtime scheduling
(default = true). This is needed for reliable
low-latency performance. On many systems, it requires
jackd to run with special scheduler and memory
allocation privileges, which may be obtained in several
ways.
-r,
--no-realtime
Do not use realtime
scheduling.
-P,
--realtime-priority int
When running
--realtime, set the scheduler priority to
int.
--silent
Silence any output during
operation.
-T,
--temporary
Exit once all clients have
closed their connections.
-t,
--timeout int
Set client timeout limit in
milliseconds. The default is 500 msec. In realtime mode the
client timeout must be smaller than the watchdog timeout
(5000 msec).
-Z,
--nozombies
Prevent JACK from ever kicking
out clients because they were too slow. This cancels the
effect any specified timeout value, but JACK and its clients
are still subject to the supervision of the watchdog thread
or its equivalent.
-u,
--unlock
Unlock libraries GTK+, QT,
FLTK, Wine.
-v,
--verbose
Give verbose output.
-c,
--clocksource ( c(ycle) |
h(pet) | s(ystem) )
Select a specific wall clock
(Cycle Counter, HPET timer, System timer).
-V,
--version
Print the current JACK version
number and exit.
ALSA BACKEND
OPTIONS
-C, --capture [ name ]
Provide only capture ports,
unless combined with -D or -P. Parameterally set
capture device name.
-d,
--device name
The ALSA pcm device name
to use. If none is specified, JACK will use
"hw:0", the first hardware card defined in
/etc/modules.conf.
-z,
--dither
[rectangular,triangular,shaped,none]
Set dithering mode. If
none or unspecified, dithering is off. Only the first
letter of the mode name is required.
-D,
--duplex
Provide both capture and
playback ports. Defaults to on unless only one of -P
or -C is specified.
-h,
--help Print a brief usage message
describing only the
alsa backend
parameters.
-M,
--hwmeter
Enable hardware metering for
devices that support it. Otherwise, use software
metering.
-H,
--hwmon
Enable hardware monitoring of
capture ports. This is a method for obtaining "zero
latency" monitoring of audio input. It requires support
in hardware and from the underlying ALSA device driver.
When enabled,
requests to monitor capture ports will be satisfied by
creating a direct signal path between audio interface input
and output connectors, with no processing by the host
computer at all. This offers the lowest possible latency for
the monitored signal.
Presently
(March 2003), only the RME Hammerfall series and cards based
on the ICE1712 chipset (M-Audio Delta series,
Terratec, and others) support --hwmon. In
the future, some consumer cards may also be supported by
modifying their mixer settings.
Without
--hwmon, port monitoring requires JACK to
read audio into system memory, then copy it back out to the
hardware again, imposing the basic JACK system latency
determined by the --period and
--nperiods parameters.
-i,
--inchannels int
Number of capture channels.
Default is maximum supported by hardware.
-n,
--nperiods int
Specify the number of periods
of playback latency. In seconds, this corresponds to
--nperiods times
--period divided by
--rate. The default is 2, the minimum
allowable. For most devices, there is no need for any other
value with the --realtime option. Without
realtime privileges or with boards providing unreliable
interrupts (like ymfpci), a larger value may yield fewer
xruns. This can also help if the system is not tuned for
reliable realtime scheduling.
For most ALSA
devices, the hardware buffer has exactly
--period times
--nperiods frames. Some devices demand a
larger buffer. If so, JACK will use the smallest possible
buffer containing at least --nperiods,
but the playback latency does not increase.
For USB audio
devices it is recommended to use -n 3. Firewire
devices supported by FFADO (formerly Freebob) are configured
with -n 3 by default.
-o,
--outchannels int
Number of playback channels.
Default is maximum supported by hardware.
-P,
--playback [ name ]
Provide only playback ports,
unless combined with -D or -C. Optionally set
playback device name.
-p,
--period int
Specify the number of frames
between JACK process() calls. This value must be a
power of 2, and the default is 1024. If you need low
latency, set -p as low as you can go without
seeing xruns. A larger period size yields higher latency,
but makes xruns less likely. The JACK capture latency in
seconds is --period divided by
--rate.
-r,
--rate int
Specify the sample rate. The
default is 48000.
-S,
--shorts
Try to configure card for
16-bit samples first, only trying 32-bits if
unsuccessful. Default is to prefer 32-bit samples.
-s,
--softmode
Ignore xruns reported by the
ALSA driver. This makes JACK less likely to disconnect
unresponsive ports when running without
--realtime.
-X,
--midi [seq|raw]
Specify which ALSA MIDI system
to provide access to. Using raw will provide a set of
JACK MIDI ports that correspond to each raw ALSA device on
the machine. Using seq will provide a set of JACK
MIDI ports that correspond to each ALSA
"sequencer" client (which includes each hardware
MIDI port on the machine). raw provides slightly
better performance but does not permit JACK MIDI
communication with software written to use the ALSA
"sequencer" API.
COREAUDIO
BACKEND PARAMETERS
-c --channels
Maximum number of channels
(default: 2)
-i
--inchannels
Maximum number of input
channels (default: 2)
-o
--outchannels
Maximum number of output
channels (default: 2)
-C
--capture
Whether or not to capture
(default: true)
-P
--playback
Whether or not to playback
(default: true)
-D
--monitor
Provide monitor ports for the
output (default: false)
-D
--duplex
Capture and playback (default:
true)
-r
--rate
Sample rate (default:
44100)
-p
--period
Frames per period (default:
128). Must be a power of 2.
-d
--device
CoreAudio device name (default:
none)
-I
--input-latency
Extra input latency (frames)
(default: 0)
-O
--output-latency
Extra output latency (frames)
(default: 0)
-l
--list-devices
Display available CoreAudio
devices (default: false)
-H
--hog
Take exclusive access of the
audio device (default: false)
-L
--async-latency
Extra output latency in
asynchronous mode (percent) (default: 100)
-G
--grain
Computation grain in RT thread
(percent) (default: 100)
-s
--clock-drift
Whether to compensate clock
drift in dynamically created aggregate device (default:
false)
DUMMY
BACKEND PARAMETERS
-C, --capture int
Specify number of capture
ports. The default value is 2.
-P,
--playback int
Specify number of playback
ports. The default value is 2.
-r,
--rate int
Specify sample rate. The
default value is 48000.
-p,
--period int
Specify the number of frames
between JACK process() calls. This value must be a
power of 2, and the default is 1024. If you need low
latency, set -p as low as you can go without
seeing xruns. A larger period size yields higher latency,
but makes xruns less likely. The JACK capture latency in
seconds is --period divided by
--rate.
-w,
--wait int
Specify number of usecs to wait
between engine processes. The default value is 21333.
NETONE
BACKEND PARAMETERS
-i, --audio-ins int
Number of capture channels
(default: 2)
-o,
--audio-outs int
Number of playback channels
(default: 2)
-I,
--midi-ins int
Number of midi capture channels
(default: 1)
-O,
--midi-outs int
Number of midi playback
channels (default: 1)
-r,
--rate int
Sample rate (default:
48000)
-p,
--period int
Frames per period (default:
1024)
-n,
--num-periods int
Network latency setting in no.
of periods (default: 5)
-l,
--listen-port int
The socket port we are
listening on for sync packets (default: 3000)
-f,
--factor int
Factor for sample rate
reduction (default: 1)
-u,
--upstream-factor int
Factor for sample rate
reduction on the upstream (default: 0)
-c,
--celt int
sets celt encoding and number
of kbits per channel (default: 0)
-b,
--bit-depth int
Sample bit-depth (0 for
float, 8 for 8bit and 16 for 16bit) (default: 0)
-t,
--transport-sync int
Whether to slave the transport
to the master transport (default: true)
-a,
--autoconf int
Whether to use Autoconfig, or
just start. (default: true)
-R,
--redundancy int
Send packets N times (default:
1)
-e,
--native-endian int
Dont convert samples to network
byte order. (default: false)
-J,
--jitterval int
attempted jitterbuffer
microseconds on master (default: 0)
-D,
--always-deadline int
always use deadline (default:
false)
OSS BACKEND
PARAMETERS
-r, --rate int
Specify the sample rate. The
default is 48000.
-p,
--period int
Specify the number of frames
between JACK process() calls. This value must be a
power of 2, and the default is 1024. If you need low
latency, set -p as low as you can go without
seeing xruns. A larger period size yields higher latency,
but makes xruns less likely. The JACK capture latency in
seconds is --period divided by
--rate.
-n,
--nperiods int
Specify the number of periods
in the hardware buffer. The default is 2. The period size
(-p) times --nperiods times
four is the JACK buffer size in bytes. The JACK output
latency in seconds is --nperiods times
--period divided by
--rate.
-w,
--wordlength int
Specify the sample size in
bits. The default is 16.
-i,
--inchannels int
Specify how many channels to
capture (default: 2)
-o,
--outchannels int
Specify number of playback
channels (default: 2)
-C,
--capture device_file
Specify input device for
capture (default: /dev/dsp)
-P,
--playback device_file
Specify output device for
playback (default: /dev/dsp)
-b,
--ignorehwbuf boolean
Specify, whether to ignore
hardware period size (default: false)
SUN BACKEND
PARAMETERS
-r, --rate int
Specify the sample rate. The
default is 48000.
-p,
--period int
Specify the number of frames
between JACK process() calls. This value must be a
power of 2, and the default is 1024. If you need low
latency, set -p as low as you can go without
seeing xruns. A larger period size yields higher latency,
but makes xruns less likely. The JACK capture latency in
seconds is --period divided by
--rate.
-n,
--nperiods int
Specify the number of periods
in the hardware buffer. The default is 2. The period size
(-p) times --nperiods times
four (assuming 2 channels 16-bit samples) is the JACK buffer
size in bytes. The JACK output latency in seconds is
--nperiods times
--period divided by
--rate.
-w,
--wordlength int
Specify the sample size in
bits. The default is 16.
-i,
--inchannels int
Specify how many channels to
capture (default: 2)
-o,
--outchannels int
Specify number of playback
channels (default: 2)
-C,
--capture device_file
Specify input device for
capture (default: /dev/audio)
-P,
--playback device_file
Specify output device for
playback (default: /dev/audio)
-b,
--ignorehwbuf boolean
Specify, whether to ignore
hardware period size (default: false)
PORTAUDIO
BACKEND PARAMETERS
-c --channel
Maximum number of channels
(default: all available hardware channels)
-i
--channelin
Maximum number of input
channels (default: all available hardware channels)
-o
--channelout
Maximum number of output
channels (default: all available hardware channels)
-C
--capture
Whether or not to capture
(default: true)
-P
--playback
Whether or not to playback
(default: true)
-D
--duplex
Capture and playback (default:
true)
-r
--rate
Sample rate (default:
48000)
-p
--period
Frames per period (default:
1024). Must be a power of 2.
-n
--name
Driver name (default: none)
-z
--dither
Dithering mode (default:
none)
environment
JACK is evolving a mechanism for automatically starting the
server when needed. Any client started without a running JACK
server will attempt to start one itself using the command line
found in the first line of $HOME/.jackdrc if it exists, or
/etc/jackdrc if it does not. If neither file exists, a
built-in default command will be used, including the -T
flag, which causes the server to shut down when all clients have
exited.
As a transition, this only happens when $JACK_START_SERVER
is defined in the environment of the calling process. In the
future this will become normal behavior. In either case, defining
$JACK_NO_START_SERVER disables this feature.
To change where JACK looks for the backend drivers, set
$JACK_DRIVER_DIR.
$JACK_DEFAULT_SERVER specifies the default server name. If
not defined, the string "default" is used. If set in their
respective environments, this affects jackd unless its
--name parameter is set, and all JACK clients unless they
pass an explicit name to jack_client_open().
see also
http://www.jackaudio.org
The official JACK website with news, docs and a list of JACK
clients.
http://jackaudio.org/email
The JACK developers’ mailing list. Subscribe, to take part in
development of JACK or JACK clients. User questions are also
welcome, there is no user-specific mailing list.
http://www.jackosx.com/
Tools specific to the Mac OS X version of JACK.
http://www.alsa-project.org
The Advanced Linux Sound Architecture.
bugs
Please report
bugs to
http://trac.jackaudio.org/
authors
Architect and
original implementor: Paul Davis
Original design
Group: Paul Davis, David Olofson, Kai Vehmanen, Benno
Sennoner, Richard Guenther, and other members of the Linux
Audio Developers group.
Programming:
Paul Davis, Jack O’Quin, Taybin Rutkin, Stephane Letz,
Fernando Pablo Lopez-Lezcano, Steve Harris, Jeremy Hall,
Andy Wingo, Kai Vehmanen, Melanie Thielker, Jussi Laako,
Tilman Linneweh, Johnny Petrantoni, Torben Hohn.
Manpage written
by Stefan Schwandter, Jack O’Quin and Alexandre
Prokoudine.