jack_delay is a small command line JACK app you can use to measure the
latency of your sound card. It uses a phase measurements on a set of
tones to measure the delay from the output to the input. Accuracy is
about 1/1000 of a sample.

Definitely read the docs in /usr/doc/jack_delay-$VERSION/README to
understand how to use this.

This package uses POSIX filesystem capabilities to execute with
elevated privileges (required for realtime audio processing). This
may be considered a security/stability risk. Please read
http://www.slackbuilds.org/caps/ for more information. To disable
capabilities, pass SETCAP=no to the script.