Apparatus and methods for processing an audio signal. The apparatus may include a digital signal processor (“DSP”) configured to receive an audio signal from a vehicular audio signal line. The audio signal may include a flat component and a compensatory component. The flat component may correspond to the audio signal in a state before combination with the compensatory component. The compensatory component may include an OEM EQ component. The apparatus may include a microprocessor in electronic communication with the DSP. The microprocessor may be configured to retrieve from the memory a restorative signal component. The microprocessor may be configured to instruct the DSP to apply the restorative signal component to the audio signal to reduce the audio signal to the flat component.