Broadcast Engineering - April 2008 - (Page 33)

PRODUCTION CLIPS DIGITAL HANDBOOK Use these techniques to resolve sound issues. ne of the challenges facing broadcasters today is the difﬁculty of presenting consistent audio in the home, especially with the increase in the number of home theatre systems with surround sound. The issues are many and varied — clicks and pops during transitions between programming, loudness variations between commercials (too loud) and programming (not loud enough), proper signaling of the home audio receiver/ampliﬁer with audio metadata, video-to-audio timing or lip sync issues, and stereo versus surround sound imaging. Today, several audio processing techniques exist that broadcasters can employ to improve the viewers’ audio experience. They include upmixing, downmixing, audio compression, audio metadata, loudness measurement and correction, and lip sync measurement and correction. This article consists of two parts. Part 1 will examine overriding issues Audio processing for HDTV, Part 1 BY RANDY CONROD O and introduce two key ways to overcome them. The second article will appear in the May issue and continue the discussion about solutions. The goal is to examine the range of audio processing techniques currently available and see how they can best be used to enhance your viewers’ experience. The articles offer tips you can use to address problems that might develop when adding new audio processes into an existing system, such as embedded or separate audio and audio paths, and how you can use video delays to maintain lip sync. Deﬁnitions Television audio originally consisted of only one channel, known as monaural or mono for short. In the ’80s, television began transmitting two-channel or stereo audio. Twochannel audio contains little depth information and primarily limits audio images to a left-to-right placement. Since the late ’90s, surround sound 5.1 has been steadily rolling out. If six channels aren’t enough to get your ears spinning, 7.1 audio with eight channels of audio is poised to be the next evolution in surround sound technology. The audio process In an ideal system, audio is processed in a transparent manner. Levels at the input and output match, and channels are not swapped (i.e., left for right in a stereo signal) or inverted electrically. There is no lip sync issue, as all video paths and audio paths match in time. Voice-over is the only extra audio processing required. In this perfect world, audio metadata is passed from the source to the ﬁnal-destination Dolby Digital AC-3 encoder without being lost or altered in any way. This ensures that the original audio mix and level move from the recording studio into the home environment as the audio engineer intended. Audio production 5.1 AES AES SD Upconverter (add audio metadata) HD Record edit playback Master control Up mix or pass thru AES Audio down mix 5.1 to 2.0 Dolby digital (AC-3) encoder 2.0 MPEG encoder 5.1 HD Dolby E audio metadata decode, embed (5.1) HD 2.0 De-embedder Figure 1. If station infrastructure is stereo, 5.1 sources are downmixed to pass through master control April 2008 | broadcastengineeringworld.com 33 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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