For a dog to be obedient in a command, it takes several things.
The dog must be shown the command.
The behavior needs to be generalized in a variety of situations.
The behavior must be practiced under increasing distraction and finally proofed with corrections (if necessary) under distraction
Until these things happen, all the aggressive voice commands in the world won't make any difference, except to possibly make the dog afraid of trying new things.
Any sound or signal can be used as a command. The only reason to raise your voice is so the dog can hear you or to get its attention if distracted. There is no need to say SIT in an aggressive tone.