After grasping the basic idea of breathing exercise breathing out with sounds, have a look at the variety of breathing methods.
In some schools or Dojos, breathing exercise breathing out with sounds finishes in 1 hour, and in others practice 1 hour and 20 minute break and practice 1 hour again and 20 minute break again, and repeat it forever.
There are some religious groups or Aikido Dojos teach those breathing methods. So if you are crazy about breathing methods and interested in those exercises, search those schools, work your way into it, and good luck.
There are various kind of breathing methods, such as; mixing with Daishuten and Shoshuten, inhaling as though inhaling the air from soles of feet and circulate it throughout the Ninmyaku (a Chinese herbal medical term; one of the Keiraku) and breath out through nose, or inhale from Hyakue (top of head) to draw cosmic energy from the whole universe when you breath in, which sounds as if the guru/instructor/teacher/leader is the God or something who has got a miracle power. But, in fact, the miracles which are said to be performed by those guru/instructor/teacher/leaders are usually fish stories. So do not expect too much from them.
No matter what kind of energy, Ki energy in universe or the earth's energy or tree's energy or whatever, you absorb, it would have little or no effect on your body.
When a religious leader or guru or whoever who can control Ki energy does "Tekazashi (put a hand on people and send Ki energy into body) to people who do not know about Ki energy or on beginners who just started to be able to feel Ki energy, the one who was sent Ki energy will be super surprised by the sensation, say "Wow, amazing! the guru/instructor/teacher/leader relieved my stiff neck! He/she must be my savior! Thank God!", and perfectly be trapped by the group/organization/movement, and be swindled out of a fortune.
Enjoy the experiences but it is important to keep a detached stance so that you can say "So what?" any time.
I have been to lots of those kinds of schools and groups and organizations and movements. While some people say that his/her disease was cured completely, some passed away, sometime even instructor or guru himself get sick or, moreover, died of cancer. It is not surprising that all those natural things happen because those are natural. And I have never seen guru or instructor or leader or whoever somebody who has got a miracle power.
Anyway, breathing method is such an endless issue, so what's next?
When I stop to think about it, yes, the next topic would be about:
Chinese Kiko (Qigong/Chi Kung)!!!!