Demonstrate the high-level to low-level processors required for connecting OEM Head Units to an after-market car audio system. Innovations in automotive technology have increased the complexity of mobile audio installations. If you want to showcase products that are designed to enhance factory OEM sound systems, the Audio Authority® Model 952 is the key. The OEM system high-level audio signals must be converted, via a third party processor, to low-level signals. The Low-Level Bus connections from the Model 952 are routed to the low-level output connections on a Model 911B Head Unit Module. Each 952 switches four processors.