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A 20 dB Audio Noise Reduction System for Consumer Applications

A 20 dB noise reduction system, designated C-type, for use in cassette tape recording and similar applications is described. An arrangement of two compressors and two expanders in cascade has been developed in which the signal-to-noise ratio improvement is compounded without significant accompanying increases of the overall maximum maximum compre;ssion and expansion ratio. Overshoots, modulation distortion, and noise modulation are well controlled. The maximum demands made on transmission channel uniformity are generally unchanged from those associated with the B-type system, although the uniformity requirements extend over a greater range of signal frequencies and levels. An improvement has been made in one condition of compressor/expander mistracking, namely, low-level mid-frequency signals in combination with dominant signals in the region above 10 kHz and incorrect channel response at such frequencies. A further development reduces the tendency of highly equalized channels to saturate, thereby increasing the useful signal levels which can be handled.


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