[LAT] Document on using Jack Apps

Hello: I am very much new to Linux and Linux audio. I am trying to measure audio IO latency for my system. Jdelay seems to be the right tool but when I run it on the terminal, I am getting message "Signal below threshold..." which probably might be because Jack is trying to capture audio and ends up getting the low noise floor because I do not have meaningful signal source connected. But then I tried to patch the this App to the qJACKctl app but the settings console is not straight forward to interpret. as it involved many parameters. I guess there are # of frames per period that may eventually be used to calculate the target latency but *is there a step-by step document description for Jdelay and any other JACK tools and also using JACK audio server in an effective manner*? Also, qJACKctl console does not offer options for very low sampling rates like 8 KHz. With ALSA, this should be possible but may be this particular tool does not support it. Can anyone help here? Thanks, -F