bionic (1) jack_iodelay.1.gz

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 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.