Abstract: Improved telephone cable conductor pair identifier apparatus incorporates an "Expander" which is interposed at an appropriate location in the amplifier and filtering circuitry between the pick up probe and the audio signal emitter, or speaker. The "Expander" acts to accentuate the differences in the amplitudes of signals present, thereby significantly enhancing the effective sensitivity of a human operator to signal amplitude differences, with a resulting remarkable improvement in the ability of the human operator to readily and accurately locate and select a telephone cable conductor being sought. Switch means may be provided to permit the "Expander" to be bypassed at the will of the human operator, since it may be desirable to use the "Expander" only in the more difficult cases of conductor pair identification.