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Free Silence Sensor Offers Worthy Set of Features

An especially handy freeware program for Windows

In the world of radio there’s no greater sin than “dead air.” Avoiding it has become increasingly complicated. Stations find themselves responsible for multiple content delivery methods, some of which have enough delay that they cannot realistically be monitored in real time by an operator on duty. Within a typical cluster, there might be several analog signals, HD Radio digital signals, multicasts, webcasts and more.

A major tool in dealing with this problem is the silence sensor. Silence sensors are designed to trigger an alarm of some kind whenever audio levels fall below a given volume for a given duration.

 They aren’t perfect; a loud roar of static won’t cause your silence sensor alarm, but it sure will put a dent in your PD’s antacid budget … not to mention your audience. Still, it’s a valuable tool.

What if you don’t have the budget, though, or (for computer-based audio) can’t tie up a valuable audio output?

Enter the Pira CZ Silence Detector. This especially handy freeware program for Windows (Win95 to Win7, or Linux via WINE) will monitor the audio input or output via the Windows Sound Mixer, and has an adjustable level threshold and time duration for both silence and return-from-silence for the alarm.

The alarm is impressive, with a hierarchical system that includes pauses and multiple actions, such as emailing a message, attempts to kill a program, start (or re-start) a program, save a screenshot (and attach it to an email), play a sound clip, send an HTTP query or reboot the system.

For example, let’s say you feed your transmitter with a high-quality OGG/Shoutcast stream, played by Winamp on a computer at your transmitter site. Pira can monitor for silence and can be programmed to make the following responses if the stream fails:

• Email a custom alarm message to a group of people.
• Force-close Winamp.
• Wait 10 seconds.
• Open a M3U (associated in Windows to open in Winamp) to relaunch the stream.
• Wait 60 seconds for the stream to buffer, and if still nothing …
• …open a different M3U with local MP3s to keep something on the air while the engineer investigates.

 And if re-starting the stream is successful, Pira can wait a user-definable amount of time before initiating a just-as-flexible list of commands for “return from silence.”

You can download a free copy of Pira from

Aaron Read is the director of engineering at Rhode Island Public Radio in Providence, R.I.