If your installation includes a hybrid key system instead of a single-line telephone, there may be a loss of up to 3 dB across that system in each direction. To compensate for that loss in any application, you will have to adjust the input/output levels accordingly.
In the test setup shown in the figure below, you will need only 1 dB attenuation on voice channel No.1 for an input level value of -4 dBm. Similarly, when adjusting the output level on voice channel No.1, you will most likely require little or no attenuation in order to maintain the output level at -12 dBm. In all other respects, this adjustment procedure is the same as the single-line telephone adjustment procedure described in the previous section.
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