Abstract: In order to determine the maximum level of a coded signal from a selected communication channel appearing in the output of a PCM multiplexer in which bit groups from several such channels are interleaved in a time-division mode, PCM bytes arriving in time slots assigned to the selected channel are fed to a comparator which causes their entry in a primary register if their numerical value exceeds that of a previous entry. After a predetermined number of PCM frames, e.g. 64, a peak-level byte represented by the contents of that primary register is transferred to a first secondary register whereupon the same procedure is repeated two more times with storage of additional peak-level bytes in two other secondary registers. In a fourth operating phase the contents of the three secondary registers are compared and, if identity is established between at least two of the bytes stored there, such a stored byte is delivered to a decoder controlling an oscilloscope to display the detected signal level.