Managing HDTV sound
Jun 1, 2009 12:00 PM, Randy Conrod
5.1 audio implementation requires comprehensive understanding.
If interconnection is considered a minor annoyance, then the mapping of the audio across many channels can be downright problematic, because an industrywide standard does not exist. TV networks have different ways of processing and mapping audio. Equipment that can easily be routed for audio processing is necessary whether the interface is AES or embedded, and using detection can assist with the different mappings. PCM and non-PCM can be detected, but identifying Dolby E versus Dolby Digital can be difficult.
Other than the 5.1 + 2.0 scenario that exists for stereo and surround sound in today's content, there is also secondary audio information that must be considered, which may be another language or descriptive video. Stereo or an upmix can be provided in cases where 5.1 is not present; however, handling the secondary audio program requires additional audio processing. If no descriptive video audio content exists, it is typically substituted by the stereo signal or a sum of the stereo signal.
5.1 in the home environment
Even if the audio is provided as 5.1 in the home environment, proper setup of the home receiver is necessary to ensure the best possible sound. Speaker placement and level alignment are important, as is the setting of the Dynamic Range Control (DRC). This will eliminate the need to reach for the volume button on the remote control every time the audio is too loud or soft.
Conclusions
There are many considerations for audio processing in today's 5.1 systems. Accommodations for monitoring the various forms of audio must be made. Lip sync will continue to rear its ugly head as systems become more complex, so a solid understanding of where lip sync can go wrong is critical.
The procedures for mapping the various channels of audio at the input and output of a system must also be well understood, and it is critical that processing be in place to handle every scenario. Audio can be transported as AES or embedded, PCM or non-PCM, and stereo or surround sound, and there may be other content that needs to be considered such as a secondary language or descriptive video.
The complications that may arise from either the purist's or nonpurist's methods of upmixing stereo must also be understood, because there may be audio metadata and upmixing issues that create unnatural sound. And, of course, correct home receiver setup is critical for the best possible surround-sound experience.
Randy Conrod is product manager of digital products for Harris Broadcast Communications.
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