Breathing in and out through the nose, also can be done trough the mouth, pulling the abdomen in during the exhalation towards the diaphragm, and out, in the inhalation. It is very fast, as fast as 2 or 3 times per second, and very loud. The people next to you should be able to hear you. When perfected the rate should be 120 to 180 cycles per minute!!
Do not expect to do it perfectly well the first time, although this can be possible for some lucky ones. Instead, you can start beginning by pushing the abdomen in while exhaling forcefully, and loudly, making more emphasis in the exhalation, and start to building it up from there, until you inhale the same amount of air that you exhale. This is a very balance breath. Both inhalation and exhalation have equal power.
Another way to start is practicing Breath of Fire for a few minutes in thirty sec periods, and alternating it in between with Long Deep Breath. You can build it from there to forty five seconds periods for two or three minutes. Soon you will be able to do it for long periods of time without stopping or struggles.
Siento que le saliera en ingles. Aqui esta el enlace con la explicacion en castellano.