 Within 10 to 20 years, the original reel-to-reel high fidelity tape recorders which did not need noise reduction were eventually replaced by cassette decks for home use.The dominant noise reduction scheme "Dolby B" was widely accepted because if an inexpensive cassette player lacked the switch, they would just sound brighter which often offset the dull sounds of cheap players.The signal to noise ratio is simply how large the music signal is compared to the low level of the "noise" with no signal.