In 1987, a member of the RIAA proposed a system where DAT recorders would have copy protection in them. The copy protection would look for the presence of frequencies in a particular high-frequency band; if there was no audio present in this band, the recorder would assume that the music in question was copy protected, and would not allow recording of the music. The record companies would then release all music with this particular frequency band filtered out. It would be illegal to manufacture a DAT machine with the presence of audio in this frequency band; the RIAA was lobbying Congress to make this the law of the land.