Super D: SANYO Noise Reduction Demo

Here's a breakdown from the owner's manual, circa 1980s:
"Super D - Theory of Operation
Cassette tape decks are popularly used among audiophiles for sound recording and reproduction. Despite their many excellent performance characteristics, there are some problems which have remained unsolved. Of these, the most notable one derives from the slow tape speed and the narrow sound tracks, which make it difficult to tape-record and play back record music.
By the combined application of the level compression-expansion techniques and the newly(1980's) developed complementary band divider, the SUPER D system of SANYO compresses (encodes) sound signals in the recording process and restores them to their original condition by expanding (decoding) them in the playback process. This is, accordingly, a kind of compander system...
The SANYO SUPER D (model PLUS N55) unit, when applied, expands the dynamic range of a cassette tape deck approximately 100 times (by about +40dB) wider than when it is not in use. At the same time, noise can be reduced to about 1/100 (by about -40dB). Thus, clear high-fidelity sound can be reproduced over a very wide dynamic range. Meanwhile, the breathing phenomenon (i.e. noise fluctuations due to changes in signal level) in the actual application of the SUPER D system has been reduced to an imperceptible level in incorporating into it a complementary band divider.
Effects obtained by expanding dynamic range:
The dynamic range of a tape deck is determined by its noise and saturation levels. The SUPER D unit, when applied, raises the saturation level and lowers the noise level over the entire band width. Hence, the dynamic range of the typical cassette tape recorder is expanded to about 100dB, when the SUPER D unit is applied, from about 60dB, which is normal when it is not in use. This means an improvement of approximately 40dB (=100times) in performance, giving the cassette tape deck a dynamic range even wider than those of reel-to-reel tape decks without NR.
Noise reduction:
The SUPER D unit achieves an improvement of 35 ~ 40dB in SN ratio, which is regarded as epoch-making. Consequently, hissing noise is eliminated to an almost imperceptible level.
Reduction of breathing phenomenon:
The complementary band divider incorporated in the SUPER D unit makes it possible to effect compression and expansion of signals under optimum conditions within respective band widths. Thus, the breathing phenomenon itself is reduced and noise within respective band widths is lessened to an inaudible level as it is covered by signal sound."