Abstract: A cassette duplicator machine reads signals from tracks of a master tape and records then simultaneously in tracks of a plurality of slave tapes. To control the fidelity of each recording in the slave tapes, each slave track is monitored by an auxiliary reader head spaced downtrack from the recorder head in the slave, to sample the recorded signal. The sample is then compared with a reference copied from the master tape, which reference is fed to the comparator with a time-delay compensating for the spacing between the slave heads. In one embodiment, the delay is provided by reading the master tracks again at a point spaced downtrack from the conventional master heads. In another embodiment, the master signal is sampled from the output of the conventional master head and successively passed through an averaging circuit and a delay line to the comparator, while the recording sample is also passed through respective averaging and delay circuits before feeding the comparator.