Qjackctl

QjackCtl is a Qt-based tool for controlling the JACK Audio Connection Kit. QjackCtl is free software released under the GNU GPL v2+.

Basic Functions: It automatically tries to detect audio hardware and lets the user choose subdevices for input and output from a drop-down list as well as common options for the sound server. QjackCtl then uses these selections to build and execute the right command-line for jackd.

Further References: Without the graphical help of QjackCtl it would be pretty hard to find the right parameters for jackd - and there are quite some (translated from [1])

Here are some links to help you working with Jack and QjackCtl:

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Wikipedia