JACKD(1) JACKD(1)
NAME
jackd – JACK Audio Connection Kit sound server
SYNOPSIS
jackd [options] -d backend [backend-parameters]
jackd –help
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 dif-
ferent 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: synchro-
nous execution of all clients, and low latency operation.
For the latest JACK information, please consult the web site,
OPTIONS
-d, –driver backend [backend-parameters ]
Select the audio interface backend. The current list of sup-
ported 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 privi-
leges, 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/mod-
ules.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. Other-
wise, 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 satis-
fied by creating a direct signal path between audio interface
input and output connectors, with no processing by the host com-
puter 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 real-
time 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 aggre-
gate 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 hard-
ware channels)
-o –channelout
Maximum number of output channels (default: all available hard-
ware 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)
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 hard-
ware 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
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 nei-
ther 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 develop-
ment 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 Devel-
opers 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 Prokou-
dine.
January 2016 1.9.9.5 JACKD(1)
