Here's What Rupert Nerve Designs have to say:
The 5042 is a two-channel, 1RU half-rack unit that provides a remarkable simulation of true tape sound through the inclusion of genuine tape drive circuitry. When the Tape circuit is not engaged, the 5042 may be used as a full, transformer-coupled, high-performance line amplifier that includes a Gain range of + and – 12 dB.
The Portico 5042 Two-Channel “True Tape” Emulation and Line Driver unit’s emulation circuit provides the nostalgic rounding and compression usually only achieved by the use of tape. This typically offsets the harshness often found in digital recordings. The Portico 5042 incorporates an actual tape drive circuit that feeds a tiny magnetic “head” which, in turn, is coupled to a correctly equalized, replay amplifier. The only thing missing is the tape itself and the cost!
“Record” and “Replay” controls are counter-ganged to keep overall input to output level approximately constant; it only changes as it would in a real tape recorder, with changing drive levels to the circuit, eventually resulting in saturation.
The frequency response and distortion performance of the Portico 5042’s tape circuitry is tailored to that of a typical analogue tape recorder. And users should beware: The dynamic range of a classic tape recorder is a lot less than that of the high-performance Portico circuit in which it nests!