Various trainers and institutions offer certificates of completion, indicating completion of a certain number of hours on a certain topic. Those that say they are offering certification are not using that term in the same way. They offer training of various lengths of time, with a wide variety of content. They have decided what material is relevant, and how to teach it. They are certifying that you have completed their training.
When choosing where to study sound therapy, explore the experience and credentials of the teachers. Each teacher brings a variety of expertise to their training. It may include music therapy, voice, psychoacoustics, meditation, energy medicine, crystal healing, mental health, brain biology, body-mind psychology, spirituality, or substance abuse treatment, for example. Each trainer also draws on their personal experiences of receiving sound healing. Look for someone you “resonate” with; someone who models what you want to learn.