Voice tone is very important when training a dog. Dogs only understand dog language, they do not understand our language as humans. So the best way to communicate with them is through voice tone. When your tone is harsh and loud, they will take that as a hint that you are angry; just like when they are loudly barking at a stranger. The first thing that dogs sense is your tone. So always mind your tone not your language first.
Basically, when you say “good dog” or “dumb dog” both at the same gently happy tone, it will still mean the same for them. Of course, they will eventually take note of the difference with the words used.
When your dog is acting mad or has done something wrong, do not use harsh tone while saying his or her name like “Trixie! Come here” . Or else, she will take that phrase negatively and she will no longer respond to it even you have a gentle tone. The best alternative, do not mix words with your tones. When you say “bad”, use it for disciplining purposes only. And when you say “Trixie, come”, you should use it with gentle friendly tone all throughout.
Training Dog Tips 101 