The introduction of audio processing and transmission equipment using digital technology created a new problem for the radio broadcaster. Most digital audio equipment has an inherent delay from input to output, typically in the order of 5 to 50 milliseconds. If this equipment is installed in a station's "air chain" (between the station's source equipment and the transmitter) the "on air" audio will lag the live audio coming from the mixing console by a few milliseconds. This delay is small and for most purposes insignificant. However, if monitoring "off air," live announcers will hear their own voice delayed in their headphones. While unnoticed by anyone else, this delay can be very distracting to the announcer. A simple solution is to switch the announcer's headphone monitoring point to "off console," a point before the delay is introduced. The problem with this solution is that a failure in the air chain processing, studio-to-transmitter link or transmitter itself may not be immediately detected by the announcer. Also, the console audio may sound relatively thin and "unprocessed" compared to the off-air audio. Therefore in most circumstances, this is an unsatisfactory solution.

The Solution

The Con/Air Switcher solves this problem. It is basically a two input/one output stereo switcher controlled by the control room's microphone relay. When the microphone relay is turned off, air audio is heard in the announcer's headphones. When the microphone relay is turned on, console audio is heard in the announcer's headphones. This way, the announcer hears the "off air" audio in the headphones at all times except when his or her voice is on the air. To make the console audio more closely match the "processed" sound of the off-air audio, a compressor/equalizer is contained in the "console" side of the Con/Air Switcher. Use of this processing is optional. A variable amount of compression can be added as well as bass and treble cut and boost. Operators can adjust the processing to their own tastes. A "Recall Presets" button is included to allow the operator to quickly return to a user-defined set of conditions. If desired, the Con/Air Switcher compression and equalization settings may be set and locked with an internal jumper which disables the front panel switches.

Features

Another feature of the Con/Air Switcher is a correlation detection circuit that can notify the operator if the air audio fails to correlate with the console audio. This can be used to alert the operator to an air failure during console monitoring, when it might otherwise go undetected. A front panel "Air Failure" LED illuminates to warn the operator that one or both air channels may have failed. In addition, an output is provided to control external devices (such as the Sine Systems MBC-1 Message Board Controller) in the event of an air audio failure. Optionally, the Con/Air Switcher can be made to automatically switch back to the off-air position if a correlation failure occurs after the microphone relay has turned on. This allows the operator to be notified of a possible problem by actually hearing the air audio.

Accessories

Rack Mounting Kit model CAS-1/RK

The CAS-1 ships in a small metal chassis that is suitable for placement on or under the console cabinetry. In some installations, it is preferable to mount the CAS-1 in a rack. The CAS-1/RK rack mounting kit is an aluminum panel that replaces the front of the Con/Air Switcher chassis so that it can be mounted in a single rack space.