Attenuation distortion is the distortion of an analog signal that occurs during transmission when the transmission medium does not have a flat frequency response across the bandwidth of the medium.

transmission impairment have three parts (1) Attenuation (2) Distortion (3) Noise

This is because infrared can travel farther with less distortion, i.e., it has less attenuation.

1. Because of attenuation, distortion, and noise. Atteniation is loss of signal power as it travels through the transmission medium. Distortion is caused by interactions between the signal and the transmission meddium. Noise can be generated internally or added through external interference.

It has to do with data communication. It is called the Shannon channel capacity theory where double the bandwidth equals double the highest data rate. This is of course theoretically and does not take into account white noise (thermal noise), impulse noise, attenuation distortion or delay distortion.