PRO D1 is a passive DI box: it has an unbalanced input interface, which is a 1/4-inch (6.35mm) interface, for connecting musical instruments or other unbalanced signal sources, such as electric guitars, electric basses, keyboards, etc.; and a balanced output interface, which is an XLR interface, for connecting mixers, audio interfaces or other devices that require balanced signal input. The input and output are equipped with isolation transformers to isolate ground loop current infection, and also have a 1/4-inch Thru interface, which can send unprocessed signals to other devices, such as amplifiers on stage, for live monitoring. Ground Lift: Used to disconnect the Pin1 transmission on the DI box XLR jack, preventing current from flowing along the shield between the DI and the microphone preamplifier, thereby breaking the ground loop and eliminating noise such as hum caused by grounding problems. Frequency response: 20Hz - 20kHz, which can ensure the integrity of audio signals and enable good transmission of high and low frequency signals. Input and output impedance: The input impedance is 50kΩ, and the output impedance is 600Ω, which helps to reduce signal reflection and distortion and ensure effective signal transmission;Attenuation (Pad): Used to reduce the level of the input signal to prevent signal overload. The attenuation values are 0dB, -20dB -40dB. Model: PRO D1 Colour:Black Material:ABS Package Contents: 2 x audio isolator