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Mono-a-Mono is a unique audio restoration program which operates on two-channel stereo recordings. It can act as a "de-mixer" or a "vocal remover", as well as its original function, as a "mono enhancer" for rejuvenating vintage audio recordings (33 or 45 rpm records, 78s, cylinder recordings, tapes, etc.). At the core of Mono-a-Mono is its ability to decompose a two-channel input into three separate signals: one made up of the components common to both left and right channels (the centre channel), another containing those present only on the left, and the third, those only on the right. Using all three signals, Mono-a-Mono acts as a "de-mixer", allowing the recording to be re-mixed without access to the original master tapes, so as to change the tonal balance or position of the sources within the sound stage. Using only the centre channel allows Mono-a-Mono to remove almost all the hiss and crackle associated with vintage mono recordings, as long as they have been reproduced and digitised in stereo. In this mode, it acts as a powerful "mono enhancer" which separates the noise from the signal, and outputs only the mono signal corresponding to the original recording. Finally, the program can also act as a "vocal remover" by producing separate left-only and right-only signals. In this case, the centre channel is discarded, (usually) including the lead vocals. Mono-a-Mono is unusual in that it will remove the centre channel even if it was placed off-centre by the original mixing engineer, or if left and right playback circuitry is not perfectly matched. Whichever mode of operation is used, Mono-a-Mono further enhances all its output signals by removing any obvious pops or clicks, suppressing any steady background noise (hiss), reducing the audibility of any distortion during louder periods, and applying a number of user-configurable filtering functions: high-pass rumble filter, low-pass hiss filter and a shelving equalisation filter.