jackd - JACK Audio Connection Kit sound server
jackd [options] -d backend
[backend-parameters]
jackd --help
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>.
- -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.
- -C, --internal-session-file
internal-session-file
-
Load internal clients and connections from internal-session-file.
Each line of this configuration file starts with a command. The following
commands are available:
l(oad) client-name lib-name client-args
With this command an internal JACK client will be instantiated.
client-name and lib-name cannot contain spaces. The rest of
the line will be interpreted as client-args and sent to the client
library.
c(on) source-port destination-port
With this command a source port will be connected to a destination port.
source-port and destination-port cannot contain spaces.
Comments are allowed, they start with #.
An example configuration could look like the following:
l inprocess1 inprocess
l amp1 jalv http://lv2plug.in/plugins/eg-amp
c amp:out system:playback_1
- -u, --unlock
-
Unlock libraries GTK+, QT, FLTK, Wine.
- -v, --verbose
- Give verbose output.
- -c, --clocksource (
h(pet) | s(ystem) )
- Select a specific wall clock (HPET timer, System timer).
- -V, --version
- Print the current JACK version number and exit.
- -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.
- -I --input-latency
- Extra input latency (frames) (default: 0)
- -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.
- -O --output-latency
- Extra output latency (frames) (default: 0)
- -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.
- -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.
-
-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
- Don't 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)
- -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)
- -I
--input-latency
- Extra input latency (frames) (default: 0)
- -O
--output-latency
- Extra output latency (frames) (default: 0)
- -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)
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
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().
Defining $JACK_NO_AUDIO_RESERVATION will bypass audio
device reservation via session bus (DBus). This can be useful if JACK was
compiled with DBus support but should run on a headless system.
$JACK_PROMISCUOUS_SERVER enables an alternate way of
handling the various shared resources (Unix sockets, semaphores, ...). In
this mode, the generated names will not contain the user id anymore, and the
permissions of those resources will be relaxed, allowing clients from
different users to talk with the same server. Moreover, on platforms that
support it (all POSIX variants), if set to a valid Unix group name or id,
the permissions will be restricted to that group, so only members of that
group will be able to launch clients that talk to this server. Important
note: it must be set with the same value for both server and clients to work
as expected.
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.
Please report bugs to
http://trac.jackaudio.org/
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.