a decoder capable of decoding audio signals encoded using analog noise reduction techniques , particularly dolby sr , is implemented by means of digital signal processing . the typical decoding paradigm used by analog dolby sr decoders is modified to overcome the problems caused by delay which is introduced by the digital implementation . a gain factor is factored out of the feedback transfer function and is placed in the forward signal path of each stage of the digital decoder . a single control circuit can then be used to generate coefficients which define transfer functions of each filter stage of the signal path . linear interpolation techniques are used to limit the number of coefficient entries necessary to emulate the transfer function of an analog dolby sr decoder . the digital decoder structure can be inverted to produce a digital encoder which is capable of implementing any noise reduction standard desired , including dolby sr .