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)