mixer(8) is the native command. It saves the settings on shutdown and restores them on startup. Those settings might not be saved if a different program is used, unless it has been made to work with the FreeBSD system. xfce's Audio Mixer seems to do the right thing, for example.
$ mixer
Mixer vol is currently set to 100:100
Mixer pcm is currently set to 100:100
Mixer speaker is currently set to 75:75
Mixer line is currently set to 97:97
Mixer mic is currently set to 16:16
Mixer cd is currently set to 75:75
Mixer rec is currently set to 75:75
Mixer igain is currently set to 0:0
Mixer ogain is currently set to 50:50
Mixer line1 is currently set to 75:75
Mixer phin is currently set to 0:0
Mixer phout is currently set to 100:100
Mixer video is currently set to 100:100
Recording source: mic
hint.pcm.0.vol="70"