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AUDIO LOUDNESS MEASUREMENT & CONTROL STRATEGIES FOR THE UK BROADCAST MARKET Manik Gupta Product Architect at Interra Systems. LOUDNESS MONITORING IS NOW A CRITICAL STEP IN BROADCAST WORKFLOWS A common issue that today’s broadcast, cable, and satellite operators face is inconsistent loudness. Over the years, the loudness levels of some commercials have been deliberately increased to catch audiences’ attention. Ultimately, inconsistent loudness between regular programming and advertisements has discouraged continued viewing and resulted in consumer complaints. To reduce these complaints, governments across the world have created loudness control regulations, such as the EBU’s Loudness Recommendation EBU R128 in Europe. Broadcasters must comply with this legislation, or they could face penalties. In the United Kingdom, Ofcom is the government- approved regulatory agency that upholds these requirements. LOUDNESS MEASUREMENT TECHNIQUES AND SPECIFICATIONS Loudness is the perception of sound level, making it quite subjective and difficult to measure. The first research on how the human ear hears different audio frequencies at different levels was conducted by Fletcher and Munson in 1933. The Fletcher-Munson curve(s) of equal loudness shows human ear perception against different frequencies. These contours have been utilized by multiple audio meters over the years. Voltage Unit (VU) and PPM are commonly used to measure audio level but often misused as devices for loudness measurement. Both were designed to measure the Sound Pressure Level rather than the “perceived” audio loudness. Sound engineers circumvent these meters by employing multiband compressors achieving heavy compression, thus making a softer sound louder and bringing down the peaks, making content hyper-compressed. Considering the problems in audio level based approaches, the ITU (International 58 | KITPLUS - THE TV-BAY MAGAZINE: ISSUE 113 MAY 2016 Telecommunication Union) proposed an algorithm for measuring loudness objectively, which is into its fourth revision with the latest version, 1770-4. The industry hopes to agree on a common algorithm for loudness measurement with this update. The loudness metering algorithm consists of a measurement of the energy equivalent average (Leq) with a weighting curve that forms the basis for matching an inherently subjective impression with an objective measurement. The weighting accounts for the acoustic effects of the head, low frequencies are de-emphasized, boosting high frequencies. In addition, gating concepts are applied to ensure that silence regions at the start and end of the program, or pauses between the dialogue, do not influence the overall program loudness. A technique for measuring multichannel audio is also included. Measured loudness is reported in LKFS (or LUFS) units, which stands for “Loudness, K-weighted, relative to Full Scale.” In addition to loudness, the ITU standard also defines true peak measurement for an audio signal. True peak measurement is ideally defined as a measure of maximum absolute sample value of an audio signal in a continuous time domain. The ITU standard describes one such approach where audio signal can be over- sampled by a factor of four for estimating the true peak. LOUDNESS REGULATIONS IN THE UK EBU R128 is the loudness recommendation widely used in Europe and followed in the UK. EBU R128 gives recommendations for program loudness, true peak level, and three other aspects of loudness: • Momentary loudness measures sudden changes in audio levels, e.g., gun shots, using a sliding time-window. • Short-term loudness measures more general changes in levels using a sliding window of 3 seconds. • Loudness range is based on statistical distribution of measured loudness, taking into account the difference between the softest and loudest part of the program. AN EFFECTIVE STRATEGY FOR AUDIO LOUDNESS MONITORING AND CONTROL Because of these regulations, loudness monitoring is now a critical step in broadcast workflows. As may be expected, the tools and methodology for loudness monitoring in