14.1 Crossover Features14.1.1 Input Level Controls14.1.2 Subsonic Filters14.1.3 Ultrasonic Filters14.1.4 Output Level Trims14.1.5 Output Mute Switches, Output Phase-Reverse Switches14.1.6 Control Protection14.2 Features Usually Absent14.2.1 Metering14.2.2 Relay Output Muting14.2.3 Switchable Crossover Modes14.3 Noise, Headroom, and Internal Levels14.4 Circuit Noise and Low-Impedance Design14.5 Using Raised Internal Levels14.6 Placing the Output Attenuator14.7 The Amplitude/Frequency Distribution of Musical Signals and Internal Levels14.8 Gain Structures14.9 Noise Gain14.10 Active Gain-Controls14.11 Filter Order in the Signal Path14.12 Output Level Controls14.13 Mute Switches14.14 Phase-Invert Switches14.15 Distributed Peak Detection14.16 Power Amplifier ConsiderationsReferences