• Am I right

    No.

    The hiss which Dolby noise reduction mitigates is natural noise inherent in the physical recording medium, due to the heterogeneous nature of the magnetic domains. Dolby compresses the input to move low amplitude signals further above this noise floor, then expands the output to reverse the effect.

    The high frequency signal deliberately added to make tape recording work with any kind of acceptable dynamic range is bias. It can be removed from the output with a simple low pass filter, but as it's both inaudible and beyond the reproduction range of most speakers, it doesn't have to be.

  • the hiss that dolby adds can be easily heard. record without dolby, with dolby b and with dolby c and play without dolby - you'll hear the particular hiss associated with dolby

  • play without dolby

    If you play back Dolby recordings without Dolby, you'll be listening to a compressed version. Any hiss hasn't been "added" by Dolby, it's noise in the original source which has been increased in amplitude along with any low amplitude signal in the same frequency bands.

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