Of these, only -l mentions the defaults. For the rest one needs --verbose to
find what they are.
-f N beep at N Hz, where 0 < N < 20000. As a general ballpark, the regular terminal
beep is around 750Hz. N is not, incidentally, restricted to whole numbers.
-l N beep for N milliseconds.
-r N specify the number of repetitions (defaults to 1).
-d N, -D N
specify a delay of N milliseconds between repetitions. Use of -d specifies
(P.S., not all beeps get through on my EEEPC 702.)