ndim
commented
5 years ago beep interfaces to the PC speaker, and the circuitry controlling the PC speaker only does square waves.
If you want to hear more sophisticated sounds, use a proper sound card and a software like e.g. sox to synthesize sounds:
$ beep -f 440 -l 500
$ play -n synth 0.5 square 440
$ play -n synth 0.5 sine 440
Currently it seems beep uses square waves for acoustics however, sines are softer and it would be nice to have beep output whatever it does already but as sines so for an ordinary command for example:
$ beep -f 1000 -n -f 2000 -n -f 1500
but for sines we add -t and for sine output $beep -t sine -f 1000 -n -f 2000 -n -f 1500
it would be a refreshing change to have.