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 compression and expansion ratio. Overshoots, modulation distortion, and noise modulation are well controlled. The demands made on transmission channel uniformity are generally unchanged from these associated with the B-type system. However, 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 10kHz and incorrect channel response at such frequencies. Afurther development reduces the tendency of highly equalized channels to saturate, thereby increasing the useful signal levels which can be handled.
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https://aes2.org/publications/elibrary-page/?id=11906
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