The 4 Channel Loudness option allows up to 4 channels of loudness metering and monitoring to be performed by the Rx unit (1 loudness channel per analyser module). The tools provided in the Loudness window for each channel allow the loudness of the selected stereo audio pair or 5.1 surround audio group to be measured and logged. Loudness can be measured in accordance with EBU Recommendation 128 or ITU Recommendation BS. 1770-3 which define the measurement in terms of LU (Loudness Units), LUFS (Loudness Units Full Scale) and LKFS (Loudness K-weighted Full Scale) over momentary, short term or integrated time periods. Loudness is logged as defined by EBU and ITU Recommendations, and provides Start, Pause, Continue and Reset functions. Loudness logs are created at a user-defined logging interval.