In all music, singing or playing, everything works better when you’re relaxed. 🙂 Plus, it’s supposed to be fun! Sometimes in our pursuit of new skills we forget that.
For the growl, this helped me: Without the sax, take a sip of water and gargle with it. Now, take the gargle down to just a really gentle buzz. Now, try it without the water. And don’t try to make a loud sound! Relax, repeat.
