I have realized that the volume could be decreased by using both "track volume slider" or dragging 'n dropping the "track gain bar" (that horizontal line similar to video bar opacity).
On the other hand, the "track gain bar" decreases the wave size while the "track volume slider" doesn't change the wave (in this way an audio envelop would be handy than the "track gain bar"). Other point is that the "track gain bar" just make possible to decrease the volume, being necessary to use "track volume slider" if the issue is increase it.
=> Actually, I am not sure about the usage of each of these tools. Do both really produce same output? Is there any situation in which each one has a specific usage?
Thanks in advance,