JACK_IODELAY(1)                                                                                                  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 corresponding hardware output connector to an input connector, and to connect that corresponding  hardware  cap-
       ture  port to jack_iodelay's input port. This creates a roundtrip that goes through any analog-to-digital or digital-con-
       verters 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.






1.9.7                                                       May 2011                                             JACK_IODELAY(1)