Vermont Public Television (VPT) is the statewide public broadcaster and PBS outlet for Vermont. With multiple high- and low-power television transmission facilities, the broadcaster also serves bordering regions of New Hampshire, Massachusetts, New York, and Quebec.
As it completed the rebuild of its master control facility to all HD, it became apparent that an old television broadcast problem was still lurking in the plant: program loudness inconsistencies.
The broadcaster takes great care to ensure the highest quality content is presented to viewers on all of its platforms. A major part of the quality-control process occurs when content is ingested to video servers. The ingest process accounts for only a portion of what goes out over the air, however. Satellite-delivered and local live programming, plus file-based programming contributed from various sources, complicate the quality-control process of the air product. Even though great attention is paid to dialog levels throughout the content production and delivery process, programming audio levels still were occasionally inconsistent.
Seeking a solution
While the issues that cause problem programming may lie with parties outside of its organization, it is VPT's responsibility to present viewers with, among other things, programming that has consistent loudness throughout the day.
The broadcaster determined that a device was needed to be the final arbiter over audio loudness. It was not looking to crush the audio to make it sound consistently loud as in the old days of top 40 radio. Rather, the broadcaster looked for a product that “knew” when programming was overly loud and corrected the problem automatically. Moreover, this device had to be surround-sound aware so that full 5.1 programs maintained the image, or center of mix.
The features available on modern surround-sound audio processors are wonderfully numerous. Most processors have surround upmixing and downmixing and metadata compatibility with Dolby encoding systems available. Other important features for the broadcaster were having front-panel controls and the ability to handle a separate stereo program in addition to the surround-sound channels.
The broadcaster considered many hardware- and software-related factors in the choice of the processor. Most importantly, though, the unit it chose had to sound natural using nonaggressive processing setups while still compensating for programming that was too loud. VPT tested several processors by placing them in the air chain and using them on-air. Ultimately, it chose the Orban Optimod 8585 surround-sound audio processor.
In the plant, the audio processor is installed in the air chain part of the transmission path, prior to Dolby Digital encoding equipment using discrete AES inputs and outputs. Through the use of a wizard-like setup procedure, the audio processor itself guides the installation process by asking several questions about the technical plant. The final step of the installation is supplying the unit with the dialog level of a station's transmissions. This is the level the processor uses to make the audio output compatible with the station's dialog level settings.
After placing the configured processor in its air chain, the broadcaster checked the over-the-air signal with a Dolby LM-100 loudness meter. Using the five-band TV preset with the CBS loudness controller, the broadcaster found program levels to be consistent over the entire day. The additional bonus to viewers was that this consistent loudness had a natural and open sound quality.
Using the Optimod 8585 has eliminated OTA loudness inconsistencies. VPT's viewers now benefit from a consistent loudness level and quality, and its engineering and operations staff now has one less quality issue to worry about.
Joseph Tymecki is the chief technology officer at Vermont Public Television.