 In 1971 WFMT started to transmit programs with Dolby NR, and soon some 17 stations broadcast with noise reduction, but by 1974 it was already on the decline.Dolby FM was based on Dolby B, but used a modified 25 µs pre-emphasis time constant and a frequency selective companding arrangement to reduce noise.A similar system named High Com FM was tested in Germany between July 1979 and December 1981 by IRT.