Broadcast Engineering - April 2008 - (Page 34)

PRODUCTION CLIPS DIGITAL HANDBOOK Even if this ideal model existed, the audio mixes and dynamic range variations would still occur. News, weather and sports, episodic programming and drama, situational comedy, live performances, and movies are all mixed in different ways. The combination of sources and program types can result in audio chaos if the audio engineer isn’t careful. When it comes to loudness, it is a well-known fact that two audio programs set to exactly the same VU meter level can still result in differing levels of loudness. Once you examine commercials and the variations of mixes and compression tricks used in them, it is a challenge to maintain consistent audio quality from the TV station to viewers’ homes. Even if a broadcaster passes along the program and commercial audio the way the producers intended, the audio that ﬁnally reaches the home may be inconsistent. Any stereo-to-surround and surround-to-stereo transitions will be disconcerting to the viewer because their receivers will repeatedly switch between two-channel to 5.1 channel reproduction according to source material. In addition, this switch is often accompanied with a relay click and an interruption of audio. Add to this the common concerns about loudness, or volume changes, between programs and commercials, and a TV audio engineer is faced with a daunting challenge. Fortunately, television engineers have a range of new techniques and technology upon which to draw. Let’s examine some of them more closely. Compression For contribution purposes among production facilities and for tape and server transports, compression techniques such as Dolby E (carrying eight channels onto two AES paths) are often used to move the increasing number of audio channels around a facility. Dolby Digital, which carries six audio channels on two AES audio paths, is used for surround sound in the home. In both cases, the accompanying two-channel audio signal is non-PCM and therefore cannot be monitored on a speaker system without ﬁrst being decoded. Downmix and upmix Surround sound mixes can be carried on stereo channels. Solutions include Dolby ProLogic II, NeuralTHX Surround and SRS Circle Surround. On a surround sound system, the two-channel audio signal can be carried, monitored, stored, edited and played back as a stereo audio signal. However, stereo audio signals played on a surround sound speaker system 34 broadcastengineeringworld.com | April 2008 http://broadcastengineeringworld.com

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Broadcast Engineering - April 2008 Contents Editorial HD Newsrooms Wavelet Compression Mobile TV Audio Processing for HDTV, Part 1 QoE for IPTV End Users NAB Update Asset Management Advertisers Index

Broadcast Engineering - April 2008

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