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 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.

-A device, -A device%p, -A device%c

(Linux-only) A simplified way to add additional audio I/O hardware to an instance of JACK. This argument is actually just a wrapper around the -I (internal client) version, requiring only the name of the ALSA "card" to be used. The name should NOT include any ALSA device access prefix (e.g. "hw:" or "plughw:") but can include a subdevice. If %p is added to the device name, it will be made available for playback only. If %c is added to the device name, it will be made available for capture (recording) only. If neither %p nor %c is added, it will be made available (if possible) for both capture and playback. Although device names may be visible in various places on your system, the file /proc/asound/cards shows them inside square braces.
Examples:
-A SB (adds playback and capture for the "SB" device)
-A Codec,1%c (adds capture (recording) for the 2nd subdevice of the "Codec" device)
-A MT1a2%p (adds playback the 1st subdevice of the "MT1a2" device)
The use of -A CARD is actually equivalent to -I foo:zalsa_in/-dhw:CARD and -I CARD:zalsa_out/-dhw:CARD.
The use of -A CARD%p is actually equivalent to -I CARD:zalsa_out/-dhw:CARD.
The use of -A CARD%c is actually equivalent to -I CARD:zalsa_in/-dhw:CARD

Note that this option (like -I) can be used regardless of the backend used, so even if you do not use the ALSA backend, you can still add ALSA-supported devices to an instance of JACK.

-I, --internal-client client-spec

Load client-name as an internal client. May be used multiple times. The form of client-spec can be any of the following:
client-path
client-name:client-path
client-name:client-path/init-string
client-path/init-string
The first form will cause jackd to attempt to load the client from a shared object named "client-path" with appropriate suffixes appended. If "client-path" is absolute, jackd will use that (adding a platform appropriate suffix for a shared object). If it is not absolute, jackd will look for "client-path" (with an appropriate suffix) in the same location that drivers and other JACK add-ons are located.
The second form provides "client-name" as the desired name for the client once loaded, in addition to the "client-path".
The third form provides an "init-string" in addition to a client name and path, which will be passed to the client's initialization function.
The final form does not specify the client name, but does include the path to the client's shared object file and an initializations string.
When invoking JACK from the shell, remember to quote the argument to -I if it includes spaces.

-M, --midi-bufsize [ event-count ]

Specify the size of the buffer used for MIDI ports. Units are "MIDI events per process() cycle", where an event occupies up to 4 bytes (as most common MIDI events do). The default buffer size is 2048 bytes, which is about 500 MIDI events. Typical values for event-count will range from 10 to about 1000. Be aware that using very high values along with a large number of ports may cause JACK to fail to start because of the amount of memory that would be required.

-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.

-S, --sync

This option does nothing in this implementation of JACK, but exists for command-line compatibility with JACK2 and possibly other versions.

-T, --temporary

Exit once all clients have closed their connections.

-t, --timeout int

Set client timeout limit in milliseconds. The default is 500 msec.

-X, --slave-driver driver-name

Asks the server to load the "slave" driver given by driver-name. Slave drivers can provide builtin-access to other devices and protocols; the primary slave-driver at this time is the "alsa_midi" one which provides bridging on Linux between native ALSA MIDI and JACK MIDI.

-Z, --nozombies

Prevent JACK from ever kicking out clients because they were too slow. This cancels the effect any specified timeout value.

-C, --timeout-thres time

Stop processing clients if JACK cannot complete the process cycle in time (typically caused by CPU overloading or misbehaved clients). The optional time argument specifies the number of miliseconds, during which consectutive process cycles must fail before JACK gives up (if the argument is not given, it defaults to 250). Processing will resume on the next change to the port graph (i.e. a port is added, removed, connected or disconnected)

-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

Provide bridging between ALSA MIDI and JACK MIDI (using the ALSA sequencer system). All ALSA MIDI clients and MIDI hardware that exist when jackd starts will be represented by JACK MIDI ports.
The "seq" argument has been retained from older versions of JACK, in part to provide for the possibility of alternate implementations.

COREAUDIO BACKEND PARAMETERS

-c --channel

Maximum number of channels (default: 2)

-i --channelin

Maximum number of input channels (default: 2)

-o --channelout

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 --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.

-n --name

Driver name (default: none)

-I --id

Audio Device ID (default: 0)

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.

NET 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)

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

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.

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.