Methods, techniques and apparatus identify members and characteristics of binders and/or other groups of communication lines such as those in a DSL system. Information obtained includes the identification (for example, by scanning) of significant crosstalking “offenders” and their “victims” that are affected by the crosstalk. One or a small number of modems are instructed to transmit with preselected transmit spectra, after which evidence of crosstalk in the noise spectrum data is examined for potential victim lines. Direct evidence of noise spectrum contribution by a suspected offender line may be obtained by collecting reported noise spectrum data and/or estimated noise spectrum data from potential victim lines. Also, where such direct evidence is not available, or in addition to it, other operational data showing crosstalk interference relating to potential victim lines can be used. The transmitting modem can either be on the CO/RT side or on the CPE side. Modems other than suspected offenders might transmit zero or minimal power in one or more selected frequency bands during scanning to reduce the risk that a modem and/or line not being examined for “offender” status supplies unnecessarily complicating and/or dominant crosstalk during the procedure. For DMT modulated DSL transceivers, well designed transmit spectra can be easily enforced by manipulating line profiles where such well designed line profiles cause minimal or no interruption to existing DSL customers. The invention also can be used to identify (partially or fully) the absolute values of crosstalk channels making up a channel transfer function.