Students often ask me, "Am I breathing too loud, heavy?" or "Am I breathing too soft, quiet?" My answer is that the breathing should be natural. Sri K Pattabhis Jois said the breath should be medium or free.
When you are confused or frustrated about your breath it is best to align the sound of your ujjayi breathing with the directional movements of prana and apana vayus. Listen and follow the apanic route of the out-breath as it sweeps down the spine and into the yoni at the pelvic floor base. Follow the route of the pranic in-breath by following it up and behind the belly; listen to the upward sweep of the expansive in-breath to the top of the chest.