With the American TV market now plunging headlong into a fully digital future, broadcasters nationwide are being forced to deal with new technical issues. In anticipation of this situation, Richard Cabot founded Qualis Audio, a startup firm focused on developing algorithms for analysis and processing of surround-sound streams. As one of the co-founders and former CTO of Audio Precision, Cabot brings an experienced perspective on broadcast audio measurement to Qualis Audio.
“As audio has changed from mono to stereo to surround, it’s gotten more complicated,” Cabot said. “Most people in the field are already up to their ears dealing with video issues, so we designed a product that can monitor audio completely on its own, and then tell you if there’s a problem.”
The product is called the Sentinel, and its functionality focuses on the analysis of audio streams, allowing station personnel to concentrate on other aspects of their operations knowing that the surround sound and associated stereo and mono downmixes are within specifications.
Sentinel accepts eight channels of audio — typically a 5.1 stream with two more channels used for stereo or bilingual feeds — in either analog or digital format. For digital streams, metadata is examined and crosscomparisons between channels are made to identify potential problems. Audio is metered for level and loudness; comb filters check for hum; and an algorithm searches for dropouts. All channels are monitored for phasing issues, with an added analysis of the frequency spectrum of the downmix and comparison of the sum of individual surround channels.
“We do that in the frequency domain for a reason,” Cabot said. “If a vocal is out of phase because of the way it was miked and that dialog is going to drop out in stereo or mono even though it sounds perfectly fine in surround, we can find that, even though a normal phase meter won’t see it. It’s always key to know if dialog could be lost.”
The goal of the Sentinel product design is to identify and correct audio errors that might be missed by human monitors, alerting the appropriate station personnel of both the existence and nature of the problem. Sentinel maintains a rolling daily log of all monitor functions, showing both real-time and linear time code, so it’s also easy to confirm whether viewer complaints are grounded in fact.
The Sentinel is IP-addressable, so station engineers can specify threshold conditions for various alert signals. For instance, energy loss in front channels would typically indicate a loss of dialog information — something very likely to trigger viewer complaints. Similarly, common yet difficult-to-hear errors such channel swapping between front and rear channels can be detected.
“It’s a set-it-and-forget product, but it offers extensive control over settings,” Cabot said. “There are four alarms, and you select the conditions and alert sounds and who is alerted. For equipment breakdowns like dead channel or a likely cable disconnect, an e-mail would go to the station engineer. For things like loudness issues or downmix reliability problems, where the problem is more likely to be in the program material, that alert might go to someone who deals with content issues, the program director.”
Sentinel is also ideal for remote operations, such as transmitter shacks. An internal sensor reports rack temperature, and six DC inputs are available for tracking non-audio conditions such as power and voltage. The unit includes four contact closures and can sound local audible alarms in addition to network-enabled e-mails. The unit can detect hum as well as intermittent, reversed and dead channels while monitoring loudness levels.
All monitor functions can be viewed via any typical Web browser in real time, with all bar graphs updating 12 times a second and most other functions sampling 3 times a second. A password-protected settings panel allows the user to set up the alert system, including threshold conditions and e-mail destinations. The live display is designed to convey the most important information to the viewer at a glance.
With the increased dependence on metadata inherent in the move to DTV, the possibility of incompatibilities has increased. Richard Cabot said that unlike units that display data for interpretation, “Sentinel is designed to identify the error and alert the operator to actual problems in real time. The goal is to improve the quality of audio while reducing operating costs — something that all broadcasters can understand in the current environment.”
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