Telestream Whitepaper Audio loudness—or why commercials can be annoying “Audio loudness is one of the most Overview common causes of complaints to You are sitting there quietly watching your favorite show on TV when all of a broadcasters. So much so that it is sudden the commercial comes on – BAM, WAM, BUY, BUY ... screams at being increasingly subjected to you. The purpose of the commercial is to grab your attention in the few legislation in many countries seconds of the spot. The recording engineers in the commercials production including North America, UK, agency will turn up the sound levels into the red for maximum impact and Europe and Australia.“ effect to shake you out of your slumbers. However, the effect can be to intensely annoy the viewer who reaches for the channel change, or worse, calls the TV company to complain. Audio loudness is one of the most common causes of complaints to broad- casters. So much so that it is being increasingly subjected to legislation in many countries including North America, UK, Europe and Australia. The US ‘Commercial Advertisement Loudness Mitigation Act’ (CALM) seeks to require the Federal Communications Commission to regulate the audio of commer- cials from being broadcast at louder volumes than the program material they accompany. The EBU in Europe have issued R128 loudness recommenda- tions. So how can broadcasters control the levels of commercials they receive so that loudness levels are consistent from program to commercial to trailer to program? They could play out every commercial and program, to subjectively listen to them, adjust or turn down the levels and re-encode the file, but this is usually impractical and loudness is not the same as levels. The human ear perceives loudness as a combination of the sound pressure and the dynamics of the sound. Short sudden peaks of sound level sound much louder than the same high levels when heard continuously for longer periods. The sensitivity of the human ear changes as a function of frequency, so loudness is also related to the frequency of the sound. A volume control on a professional music amplifier will alter the frequency response with loudness level to correspond approximately with that of the response characteristics of the human ear. 1 Telestream Whitepaper X Frequency XW Leq (W) weighting ∑ Loudness is a combination of audio level, dynamics and However this is for aW single mono channel. In multi- 1/T frequency, and there are many variations of algorithms channel loudness measurement, the loudness of each of the individual audio channels is measured inde- that seek to combine these to match the physiology of 2 1 T XW pendently byX theLeq FrequencyLeq(RLB) (W) = 10 log Xalgorithm beforedt takingLeq (W) the the human ear. A commonly used family of curves in W10 ∫ 2 dB T 0 ∑X mean square andweighting summing them together.Ref Pre-filtering audio loudness or noise measurement is known as W A-weighting, relating to the measurement of sound is applied to each channel prior to the measure.1/T pressure level. XL YL 2 ZL Pre-lter RLB lter Mean1 squareT XW GL Leq (W) = 10 log dt 10 ∫ 2 dB T 0 X Loudness is also relative to the surrounding ambient XR YR Ref ZR sound level or reference level. Someone speaking at Pre-lter RLB lter Mean square GR Loudness normal levels in your room at home may be perfectly XC YC ZC Pre-lter RLB lter Mean square GC ∑ X Y Z audible but speaking at the same level in the middle of XL YL ZL Ls Pre-lter RLB lter Ls Mean square Ls GL a rock concert would be inaudible. Dolby uses a ‘Dialog Pre-lter RLB lter Mean square GLs XR YR ZR XRs Pre-lter RLB lter YRs Mean square ZRs G Norm’ reference level in their AC3 audio compression Pre-lter RLB lter Mean square GRRs which is a measure of the A-weighted average level of Loudness XC YC ZC dialog within a presentation against a normal speaking Pre-lter RLB lter Mean square GC ∑ TheXLs weighting applied to YeachLs channel ZdependsLs on the level. It ranges in integer values from 31, where decoder Pre-lter RLB lter Mean square GLs gain remains at unity, to a value of 1, where decoder number and positioning of channels. Two channels of XRs Channel YRs ZWeighting,Rs Gi gain is reduced by 30 dB. stereo Pre-ltercan be combinedRLB lter with Meanthe square same weighting,GRs but withLeft surround(GL) sound the different channels1 are.0(0 dB)weight- In the broadcast world ITU-R BS.1770 specifies edRight as follows:(GR) 1.0(0 dB) ‘Algorithms to measure audio program loudness and Centre (GC) 1.0(0 dB) Channel Weighting, G true-peak audio level’ and aims to ensure that ‘for the Left surround (GLs) 1.41 (~ +1.5i dB) purpose of program exchange, it is essential to have a LeftRight (G surroundL) (GRs ) 1.411.0 (~(0 +1dB).5 dB) single recommended algorithm for objective estimation Right (GR) 1.0(0 dB) of subjective loudness’. It recommends the following Centre (GC) 1.0(0 dB) Leq(RLB) measurement algorithm — where Leq(W) the Left surround (GLs) 1.41 (~ +1.5 dB) frequency weighted sound level measure, Xw is the Right surround (G ) 1.41 (~ +1.5 dB) signal at the output of the weighting filter, XRef is the Rs reference level, and T is the length of the audio se- quence. So when Joe viewer calls to complain about the sound levels in the commercial, and the broadcast engineer checks the levels and says ‘hey none of the channels ever exceeded –5 dBFS’, there is more to it than just X Frequency XW Leq (W) weighting ∑ the peak levels that Joe was hearing as the loudness W that awoke him from his slumbers. 1/T About Telestream 2 Telestream provides world-class live and on-demand 1 T XW Leq (W) = 10 log dt 10 ∫ 2 dB digital video tools and workflow solutions that allow T 0 X Ref consumers, businesses, and organizations to transform video on the desktop and across the enterprise. Many Subjective testing was carried out by the Audio of the world’s most demanding traditional media Perception Lab of the Communications Research companies, as well as a broad range of business, XL YL ZL Pre-lterCenter, RLBCanada, lter using programMean square materialsG Lfrom televi- government, and non-profit environments, rely on sion and radio broadcasts from around the world, as Telestream products to streamline operations, reach a XR YR ZR Pre-lterwell as fromRLB lter CDs and DVDs.Mean square The sequencesGR included broader range of users, and generate more value from music, television and movie dramas, sporting events, Loudnesstheir media, while simultaneously reducing operating XC YC ZC Pre-lternews broadcasts,RLB lter soundMean effects square and commericals.GC The∑ costs. XLs reference signal usedYLs was a level of Z60Ls dBA, a level Pre-lterfound toRLB be lter a typical listeningMean square level for televisionGLs viewing For more information on file-based QC solutions, please visit: www.telestream.net/vidchecker/overview.htm XRs in actual homes. YRs ZRs Pre-lter RLB lter Mean square GRs Copyright © 2016. Telestream, CaptionMaker, Episode, Flip4Mac, FlipFactory, Flip Player, Lightspeed, ScreenFlow, Switch, Vantage, Wirecast, Gameshow, GraphicsFactory, MetaFlip, and Split-and-Stitch are registered trademarks and Mac- Caption, e-Captioning, Pipeline, Post Producer, Tempo, TrafficManager, Vidchecker Channel Weighting, Gi and VOD Producer are trademarks of Telestream, LLC. All other trademarks are the www.telestream.net | [email protected] | tel +1 530 470 1300 property of their respective owners. October 2016 2 Left (GL) 1.0(0 dB) Right (GR) 1.0(0 dB) Centre (GC) 1.0(0 dB) Left surround (GLs) 1.41 (~ +1.5 dB) Right surround (GRs ) 1.41 (~ +1.5 dB) .