Model CAS-1

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CAS-1 Con/Air Switcher

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Con/Air Switcher

Eliminate the delay caused by digital equipment from your studio air monitor. Listen your delay-free console signal while the CAS-1 monitors your air signal.

The Problem

Digital audio processing and transmission equipment 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. When this equipment is installed in a station's air chain (between the source equipment and the transmitter) the air audio will lag the live audio from the mixing console by several milliseconds.

The delay is small and for most purposes insignificant. However, live announcers will hear their own voice delayed when monitoring an air feed. While unnoticed by anyone else, this delay can be very distracting to the announcer. A simple solution is to move the monitor to a point before the delay is introduced, "off console" instead of "off air".

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. In most situations 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 microphone relay in the control room. When the microphone relay is off, the monitor audio is a live air feed. When the microphone relay is turned on, a console feed is switched into the monitor audio. This way, the announcer hears the "air audio" at all times except when he or she is speaking.

To make the console audio more closely match the "processed" sound of the air audio, the CAS-1 has a compressor/equalizer in the "console" audio feed. Using this, optional, processing, 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 using the front panel switches. A "Recall" button allows the operator to quickly return to a user-defined set of conditions.


The Con/Air Switcher has a correlation detection circuit that can notify the operator if the air audio does not closely match the console audio. This can be used to alert the operator to an air failure when the monitor feed is coming from the console audio. This is the time when an air audio failure might otherwise go undetected. Additionally, a front panel "Air Failure" indicator illuminates to warn the operator of the failure.

The audio failure indicator also provides and output that can signal external devices, such as the Sine Systems Message Board Controller, in the event of an air audio failure. The Con/Air Switcher can also automatically switch the monitor audio back to the air feed. This allows the operator to be notified of a possible problem by actually hearing the air audio.


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.