[Impulse]

I want to change the volume of a selected stave line relative to the others in a piece of music down loaded by Musician.
I choose Staff controls from the view command, click the little blue arrow only in Staff Selection and while the music is playing move the Volume slider.
This however changers the volume of all the staves not the specific one highlighted.
This is as written in instructions, but is not working. What am I doing wrong?
Thanks.