Automate NPR's All Things Considered
with the Pause Detector
see the Pause Detector
By Chris Scott, Bowling Green, Kentucky



Public radio stations have had mixed success using timed break triggers to automate NPR's All Things Considered.[and other programs such as ME, WE, TOTN, Car Talk, etc.] NPR is unique among radio networks in that for several reasons, many programs are fed without cue tones or other break-start signals. Instead, NPR producers use scheduled Atimeposts", which flank the cutaway breaks. Theoretically, these one-second pauses would be simple to target with a carefully timed automatic insertion, given the time synchronization accuracy available. In practice however, several factors conspire to cause transitions to occur during network announcer speech, resulting in "upcut" or truncated audio. A system is in use at The Public Radio Service of Western Kentucky University that effectively solves this problem, using a time-constrained "pause detector" to both trigger the break, and rejoin the network.

The Timing Environment


A cutaway beginning at the top of the minute starts with a pause at :59 seconds, plus or minus variances. Network program resumes at :00 seconds. This cycle repeats at the end of the cutaway sixty seconds or so later. The :59 outpost is variable due to the difficulty of dynamically adjusting copy and prerecorded material to reach the second precisely. The resume post is more consistent therefore, both the cutaway time and the theoretical two-second pause duration are variable. Experience has shown that the pause may occasionally be as brief as seven-tenths of a second, or during weekend programs, less. Figure 1 shows the pause timing.



Time Synchronization


The OS/2-based Satellite Operating Support System PC hardware supplied by NPR provides a convenient momentary signal each hour allowing precise automation PC sync. Many automation systems allow events to be scheduled only in integer second increments, which seriously limits break timing adjustment unless the basic clock sync is skewed. This skewing must be avoided if feeds from more than one network will be automated. If synchronized every hour, it's estimated that timing agreement between NPR and the automation clock can be maintained to less than plus or minus 100 milliseconds. With this accurate agreement, it would seem reasonable to initiate a centered cutaway at :59.5, and expect the half-second margin of error to prevent audio clashes.


Timed Breaks


Even after experiments in clock skewing, the experience at WKYU was that on average, only 80 to 90 percent of the timed breaks were handled smoothly. The most common break corruption was truncation of NPR announcer speech. This was caused primarily by human factors at NPR, which introduce timepost variances. It=s very burdensome for announcers and producers to end each audio segment at :59 seconds and resume at :00 perfectly, every time, without compromising program flow. WKYU management decided that these timed break failures impaired the air product too much to allow automation to be substituted for a human "board operator" that could judge the cutaway moment better. Further experimentation was in order.


The Novel Solution


An approach was pursued which augments timed break triggering with additional smarts to track break timing variances. A pause detector was developed that identifies absence of audible program, and signals the automation system when the duration exceeds seven-tenths of a second.

The pause detector had to provide a reliable output signal to the automation system, cue-tone-detector style. Silence sensors exist for detecting automation system stoppage, but have not been adapted for this purpose. To enhance reliability, the threshold of audibility detection was carefully controlled. The frequency response was shaped to emulate human hearing sensitivity. The well-known Fletcher and Munson response curves were modeled as the weighting factor. Since it=s also known that quick pulses of frequencies normally audible will not generally be heard if they are brief enough, the attack time of the level detector was tailored to approximate the DIN standard 45406 for peak program meters which addresses this effect. Figure 2 shows the pause detector system interconnection diagram.


Automation System Integration


Because 700 millisecond pauses are common during the body of normal network programming, premature triggering had to be prevented. WKYU uses the Cartworks PC-based audio cart replacement and automation system. This system was chosen due to its user-friendly operation and cost-effectiveness. A scripting language is provided that permits great flexibility in handling automation tasks and simultaneous background recording with parallel "script processors" allowing various combinations of simultaneous task execution. Cartworks accepts external trigger signals using a "watch window" of time that can be set as brief as 12 seconds. Only during this eligibility period will the automation react to a pause.


The pause detector is permanently connected to the network downlink demodulator. This is essential if program re-entry is to be pause controlled. Its output feeds one of Cartworks' twelve external trigger inputs. This trigger is used not only to sense cutaway breaks, but also to simultaneously record embedded promos fed during these breaks. By time-constraining the pause detector trigger, audio switch operation during the body of a program segment is prevented. The automation script event begins pause detector triggering at :57 and ends 12 seconds later. A narrower window of perhaps five seconds would be optimal, but the Cartworks minimum of 12 has proved quite satisfactory. An automation script "safety event" is included for the network rejoin, or in the case of background recording, a recorder stop. Examination of the automation logs shows that this safety feature has not yet been needed, but it was felt essential should a major network variance result in no pause at re-entry time, causing rejoin failure. It consists simply of a timed rejoin at the last possible moment.




Pause detection appears to be a robust interim automation technique to be used until NPR's adoption of cue tones or other external signaling. Automation clock sync accuracy and stability requirements are considerably reduced. The method may not be transportable to every automation system, but most should permit its use through external triggering similar to cue-tone detection. (2).

2. 2Chris Scott & Associates, P.O. Box 52, Bowling Green, KY 42101; (270) 781-5301. The completed module is $139.00 including Con US shipping. 

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