Ray Dolby, the man who revolutionized the way we hear sounds, died Thursday at age 80.

Dolby invented the Dolby noise-reduction system and digital surround-sound, and to  understand the man’s impact, you have to know a bit about audio engineering. You’ll recall that, in the olden days, sounds were once recorded on these quaint things called audio cassettes. A cassette is essentially just a plastic casing with some magnetic tape inside; when the cassette plays, the tape moves past an electromagnet in your boombox and produces an electromagnetic pulse that signals the speakers. That’s a pretty ingenious and complex process, but it has one big drawback: The magnetic particles on the tape create a hissing noise that can drown out the actual sound, particularly during quiet passages and on high frequencies.

In the MP3 digital era, that problem’s unheard of. But in the 1950s and '60s, listeners literally could not hear any recorded sound without an undercurrent of hiss in the background.

Ray Dolby’s noise-reduction systems changed all that. First released in the late '60s, “Dolby B” used a two-step process to cut down on audio cassette hiss: It boosted soft passages during the recording stage, and then lowered them back to normal levels on playback. Because lowering the soft passage levels also lowered the noise levels, listeners got less hiss.

Of course, this is all very technical and jargony, but it’s had a huge impact on the entertainment industry. Sound engineers and consumer tech companies incorporated Dolby’s technology into their recording processes and products. (You’ve probably spotted the “Dolby” logo on CD and DVD players, among many other things) Movies, beginning with 1971’s “A Clockwork Orange,” used Dolby’s system to produce crisper audio in theaters.

Ray Dolby went on to found Dolby Laboratories, now a billion-dollar business that, incidentally, brought us digital surround-sound in movie theaters and at home. The Los Angeles Times reports that more than 7.4 billion consumer products use Dolby technologies. It’s also a fixture at movie theaters, where the Dolby Digital logo will show up before or after the film screens.

Fittingly, the Kodak Theatre — where the Oscars are held — was renamed the Dolby Theatre last year. But Hollywood sound engineers aren’t the only ones who owe a debt of gratitude to Ray Dolby. Whether you realize it or not, his inventions have for years quietly shaped how, and what, you hear.