The test signal must be chosen so that its power level is within the usual operating range of the circuit being tested.

A common test for this problem is to use a 50% and a 75% grey test signal.

While two record the test signal, the other two play it back.

Signals from positive controls should cover the range of test signals.

Two of these lines in each field are reserved for test signals.

Well they don't have a test signal then.

Run it without a tape I think it is to get the test signal.

Noise is often generated deliberately and used as a test signal.

I bet they're sending different test signals, trying to get it to respond to them.

Circuit boards, are held in place and subjected to controlled electronic test signals.