sign). 3. Nonlinear performance in analog (FDM) multiplex systems. Excessive level may exacerbate crosstalk. By "excessive level" we mean that the level or signal intensity has been adjusted to a point higher than it should be. In telephony and data systems, levels are commonly measured in dBm. In cable television systems, levels are measured as voltages over a common impedance (75 ohms). See the discussion of level in Section 3.4. There are two types of crosstalk: 1. Intelligible, where at least four words are intelligible to the listener from extraneous conversation(s) in a 7-second period. Unintelligible, with crosstalk resulting from any other form of disturbing effects of one channel on another. Intelligible crosstalk presents the greatest impairment because of its distraction to the listener. Distraction is considered to be caused either by fear of loss of privacy or primarily by the user of the primary line consciously or unconsciously trying to understand what is being said on the secondary or interfering circuits; this would be true for any interference that is syllabic in nature. Received crosstalk varies with the volume of the disturbing talker, the loss from the disturbing talker to the point of crosstalk, the coupling loss between the two circuits under consideration, and the loss from the point of crosstalk to the listener. The most important of these factors for this discussion is the coupling loss between the two circuits under consideration. Also, we must not lose sight of the fact that the effects of crosstalk are subjective, and other factors have to be considered when crosstalk impairments are to be 3.4 LEVEL measured. Among these factors are the type of people who use the channel, the acuity of listeners, traffic patterns, and operating practices. 3.4 LEVEL Level is an important parameter in the telecommunications network, particularly in the analog network or in the analog portion of a network. In the context of this book when we use the word level, we mean signal magnitude or intensity. Lev