The HR-101 kit is comprised of a Sender and a remote Receiver, though they can be purchased individually. In fact the HR-101-S is often used as a low-noise balanced microphone preamp with line-level mix, and both L/R analog plus SPDIF digital outputs. The HR-101-S preamp provides an ST connector for connection to the HR-101-R receiver. The receiver outputs L/R analog and SPDIF digital audio simultaneously. As mentioned, the Sender is an ultra low-noise microphone preamp with Stereo line level mix (XLR and 3.5mm inputs). Basically the XLR input signal is first routed to a low-noise variable gain preamplifier, and then summed equally with the left and right analog inputs. The resultant signal's level is displayed on the front panel VU meter and is available on the rear panel as analog Stereo line-level on 3.5mm jack as well as Digital SPDIF on an RCA. You can use both inputs or either one. A typical application is when the L/R stereo input if from a PC (its volume level is adjusted on the PC), and it is being mixed in with a speaker using the microphone preamp. The sender front panel includes a color LED bar for VU indication, mic gain adjustment knob, and a switch for injecting phantom power in the XLR input. The sender has an ST Fiber optic connector that can connect to a corresponding receiver using one multi-mode cable upto 1,525 m (5,000 ft) away. The compact Receiver provides both Stereo Analog and Digital SPDIF outputs.