The hd Qi series is a modular, flexible hardware and software solution for operating Harmonic Design loudspeaker systems. The 2HE, 19″ rack hardware includes four balanced inputs and up to four power outputs, which can be processed through a high-performance DSP with IIR and FIR filtering technology. The associated user software hd LevelZ allows easy access to all parameters through a Windows-based computer or directly on the amplifier via the 3.2 “LCD display with navigation buttons.