Tape duplicating apparatus

In an apparatus for producing duplicate tapes by transmitting signals (V, A₁, A₂) reproduced by a master VTR (1) to a plurality of duplicating VTRs (10) for simultaneous recording on respective tapes in the latter, control signals from a bidirectional remote control unit (20) are modulated with a first modulating frequency and are transmitted over a bidirectional control signal line (BDL) to the duplicating VTRs (10). If a response is required from one of the duplicating VTRs (10), response signals from such duplicating VTR (10) are modulated with a second modulating frequency different from the first modulating frequency, and during a pause in signal transmission from the remote control unit (20), the modulated response signals are transmitted to the remote control unit (20) over the bidirectional control signal line (BDL). A test signal is transmitted to the duplicating VTRs (10) in place of the signal reproduced by the master VTR (1), and defects in the recording operation of the duplicating VTRs (10) are detected from playback of the test signal recorded by the respective duplicating VTRs (10).