A variety of noise reduction processing was used This processing was a double-ended system where the record processor boosted certain frequencies and portions of the dynamic range while the playback processor provided a complementary reduction of the signal. These systems are generally referred to as companders for compressor-expander. Two different manufacturers of companders achieved high market penetration. Two others did not, but that is not to say that their equipment was not used somewhere. To the best of my knowledge, no one has written a Direct-X-type plug-in for a computer, so you are stuck having to buy the playback processors for each system you wish to reproduce.