jack_iodelay(1) [debian man page]

JACK_IODELAY(1) 					      General Commands Manual						   JACK_IODELAY(1)

NAME

       jack_iodelay - JACK toolkit client to measure roundtrip latency

SYNOPSIS

       jack_iodelay

DESCRIPTION

       jack_iodelay  will  create  one input and one output port, and then measures the latency (signal delay) between them. For this to work, the
       output port must be connected to its input port. The measurement is accurate to a resolution of greater than 1 sample.

       The expected use is to connect jack_iodelay's output port to a hardware playback port, then use a physical loopback cable from  the  corre-
       sponding  hardware  output connector to an input connector, and to connect that corresponding hardware capture port to jack_iodelay's input
       port. This creates a roundtrip that goes through any analog-to-digital or digital-converters that are present in the audio hardware.

       Although the hardware loopback latency is the expected use, it is also possible to use jack_iodelay to measure the latency along any  fully
       connected signal path, such as those involving other JACK clients.

       Once  jack_iodelay  completes  its measurement it will print the total latency it has detected. This will include the JACK period length in
       addition to any other latency in the signal path. It will continue to print the value every 0.5 seconds or so so that if you wish  you  can
       vary aspects of the signal path to see their effect on the measured latency.

       If no incoming signal is detected from the input port, jack_iodelay will print

	Signal below threshold... .

       every second until this changes (e.g. until you establish the correct connections).

       To  use	the value measured by jack_iodelay with the -I and -O arguments of a JACK backend (also called Input Latency and Output Latency in
       the setup dialog of qjackctl), you must subtract the JACK period size from the result. Then, if you believe that  the  latency  is  equally
       distributed  between  the input and output parts of your audio hardware (extremely likely), divide the result by two and use that for input
       and/or output latency value. Doing this measurement will enable JACK clients that use the JACK latency  API  to	accurately  position/delay
       audio to keep signals synchronized even when there are inherent delays in the end-to-end signal pathways.

AUTHOR

       Originally written in C++ by Fons Adriensen, ported to C by Torben Hohn.

0-122-0 							  September 2012						   JACK_IODELAY(1)

lgrp_latency(3LGRP)													       lgrp_latency(3LGRP)

NAME

       lgrp_latency, lgrp_latency_cookie - get latency between two lgroups

SYNOPSIS

       cc [ flag... ] file... -llgrp [ library... ]
       #include <sys/lgrp_user.h>

       int lgrp_latency_cookie(lgrp_cookie_t cookie, lgrp_id_t from, lgrp_id_t to, lgrp_lat_between_t between);

       int lgrp_latency(lgrp_id_t from, lgrp_id_t to);

       The  lgrp_latency_cookie()  function  takes  a  cookie  representing  a snapshot of the lgroup hierarchy obtained from lgrp_init(3LGRP) and
       returns the latency value between a hardware resource in the from lgroup to a hardware resource in the to  lgroup.  If  from  is  the  same
       lgroup as to, the latency value within that lgroup is returned.

       The between argument should be set to the following value to specify between which hardware resources the latency should be measured:

       LGRP_LAT_CPU_TO_MEM     /* latency from CPU to memory */

       The  latency  value  is defined by the operating system and is platform-specific. It can be used only for relative comparison of lgroups on
       the running system. It does not necessarily represent the actual latency between hardware devices, and it might not  be	applicable  across
       platforms.

       The  lgrp_latency()  function  is  similiar to the lgrp_latency_cookie() function, but returns the latency between the given lgroups at the
       given instant in time. Since lgroups can be freed and reallocated, this function might not be able to provide a	consistent  answer  across
       calls. For that reason, the lgrp_latency_cookie() function should be used in its place.

       Upon successful completion, the latency value is returned. Otherwise -1 is returned and errno is set to indicate the error.

       The lgrp_latency_cookie() and lgrp_latency() functions will fail if:

       EINVAL	       The specified cookie, lgroup ID, or value given for the between argument is not valid.

       ESRCH	       The  specified  lgroup ID was not found, the from lgroup does not contain any CPUs, or the to lgroup does not have any mem-
		       ory.

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Evolving			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+

       lgrp_init(3LGRP), lgrp_parents(3LGRP), lgrp_children(3LGRP), liblgrp(3LIB), attributes(5)

								    26 Jan 2005 					       lgrp_latency(3LGRP)