The Maitri Upanishad

 ..."mentions two aspects of  Brahman, the higher and the lower. The higher Brahman being the unmanifest  Supreme Reality which is soundless and totally quiescent and restful, the  lower being the Shabda-Brahman which manifests itself into the everchanging  restless cosmos through the medium of sound vibrations. The Upanishad  says that “Two Brahmans there are to be known: One as