Audio in the HD age

Audio in the age of HD production has ushered in a host of challenges for broadcasters, production houses and educational facilities. Adding to these challenges, stations and production houses have become more reliant on novice engineers or nontechnical staff to meet increasingly complex programming demands. Audio product manufacturers have responded to these challenges with the release of digital audio consoles and stand-alone units for broadcast production that offer increasingly agile features to help support more intricate mix requirements.

The ups and downs of 5.1

Implementing 5.1 often mandates a major equipment upgrade by facilities, as the complexity of a mix situation involving simple stereo and 5.1 surround is best accomplished in a digital production workflow. While the industry is romancing HD video quality with a hint of 3-D on the horizon, the stark realities and challenges of audio still lie with stereo mixes versus 5.1 surround mixes, both on the production side and the viewer side. Where the major broadcast facility, production house and feature studio have the resources and staffing to accomplish 5.1 audio, many local affiliates and smaller production facilities may only have the means for stereo. As a result, the segment of their viewership that is equipped for 5.1, such as home theater enthusiasts, will have to put up with being jarred from the fast-paced action and lively crowd noises of a sports program when the enveloping surround field collapses into a locally produced commercial in stereo.

Fortunately, manufacturers of digital consoles and stand-alone units offer 5.1 upmix products to help this situation along. The stereo-to-5.1 upmix algorithm essentially extrapolates information from an existing stereo mix to populate the front center speaker, the left and right surround speakers, and the subwoofer. For the local content producer working in stereo, this means all productions can match the surround capabilities of the network feeds, keeping the audio field consistent. This can also add new life into legacy productions or movie catalogs. Hitting a button on a digital console is far easier than contracting to remix a production. The good news is many of the available upmix products deliver believable results.

Despite the growing consumer interest in surround sound, most industry estimates place the market penetration of home theater systems in the mid-30 percent range, indicating that the majority of viewers are still only capable of hearing that fantastic surround track in simple stereo. This can be seen in that the much-desired, latest-generation flat-screen TVs still offer integrated stereo speakers. This market dichotomy ensures that stereo will reign supreme for quite a while. To this end, the digital audio console or stand-alone unit manufacturer that provides this 5.1 upmix algorithm must also deliver a phase-accurate stereo (and/or mono) downmix from an existing discrete 5.1 mix.

The perplexities of panel discussions

Getting a handle on the delivery of simultaneous 5.1 and stereo feeds to viewers is a major component of successfully integrating surround in the broadcast workflow, but not the only one. Surround sound for panel discussions also presents new challenges. As with analog audio, having a panel with two or three members presents one level of difficulty, while adding more members, as with debates, raises the complexity level exponentially. For the engineer, the problem is dealing with how to make sure the right mic is on, and at the right level, in time for any particular speaker — all while maintaining consistent ambient noise levels for a clean listening experience. In the world of analog, this was accomplished through a combination of level gates, mind-bending concentration, quick reflexes and perhaps several cups of strong coffee.

With a digital console, engineers can use a DSP-based gating function on all mics to turn a channel on and off as before, but they still face the challenge of maintaining consistent background noise. When a gate is introduced to the signal flow, the action of turning the active mic on and off changes the ambient level balance in the stereo and surround fields, creating a “pumping” artifact that is unpleasant and distracting. Many engineers avoid this problem by setting an average fader level and manually upcutting a particular fader to present a consistent ambient field. This, of course, requires agility and some guesswork as to who might be speaking next. This might be manageable with a small number of participants speaking mostly in turn, but if there is a large number of participants, and they're arguing, it is a nightmare!

What digital technology can offer is algorithm development to automate this process. This function can be found in some stand-alone units, or better yet, as a feature that is built into the mixing console. Engineers can now set optimum levels for multiple mics, and the algorithm takes over the task of riding the levels while maintaining a smooth ambient background. Engineers are released from the shackles of keeping their hands locked on the talent mic faders and are free to react to the director barking out instructions or to focus on the overall sound quality of a production, which was often not possible in the past.

It's an automated world

Station automation is a growing requirement in today's broadcast industry. Automation provides a variety of benefits, even enabling stations to maintain a high quality of production during nonpeak programming hours, with limited staffing. The challenges listed previously, and their all-important solutions, are highly valued when operating within an automated environment.

With these advancements in digital console technology, a station's automation system can trigger a setup that would recall all the necessary parameters for a perfect stereo to 5.1 upmix, along with “hands-off” mic leveling, to provide a clean, tight sound field for viewers during the wee hours of the morning.

As the broadcast industry continues to recast its technology mission to accommodate 3-D and beyond, audio manufacturers are helping this change by providing innovative solutions to aid all levels of the industry.

Steve Zaretsky is vice president broadcast sales for Solid State Logic.