What is the ruling on vocalizing the post-prayer remembrances, and what is the meaning and method of "ikhfat" (quiet recitation)?

The prescribed manner for the tasbih (glorification) in bowing (ruku') and prostration (sujud) is that it should be silent, not audible. This is further emphasized if vocalizing it would disturb other worshippers. "Ikhfat" (softness) is the opposite of "jahr" (audibility).