The goal of this clinical trial is to learn if the addition of frequency filtered music (Safe and Sound Protocol) to daily cognitive processing therapy improves effectiveness for reducing PTSD symptoms. The main questions it aims to answer are: * Does the addition of frequency filtered music reduce PTSD symptoms for patients receiving cognitive processing therapy for PTSD? * Does the addition of frequency filtered music to cognitive processing therapy improve stress physiology (arousal)? * Does improvement in physiological stress regulation help explain improvements in hyperarousal and PTSD symptoms? Researchers will compare the effects of a frequency filtered classical music playlist to an identical playlist without added filtering. Participants will be randomized to a music playlist. Participants will: * Receive 10 daily sessions of cognitive processing therapy * Listen to 15 minutes of music before their therapy sessions (2.5 hours music listening total). * Complete clinical interviews and questionnaires before, during, and up to 6 months after therapy. * Have their physiological arousal monitored during listening and therapy sessions * Wear a Fitbit device and complete smartphone surveys for 4 weeks