Who is the most famous person in the world?
It must be Ray Dolby, inventor of the Dolby noise reduction system – his famous Dolby button is to be seen on just about every hifi cassette deck in the world.
But most people actually think that the Dolby system is bad. All it does is make the sound dull. That however displays a lack of knowledge of the system's true purpose.
Analog tape recorders are prone to noise. Cassette decks even more so because the tape is very narrow. Tape hiss is clearly audible beneath the music and between tracks.
The Dolby system works by boosting low-level signals during the record process, then cutting them back to where they should be on replay. This also brings down the noise level.
The trick in the design of any noise reduction system is to get it to work well, but without the noise background audibly going up and down in level. This would sound worse than not using noise reduction at all. The Dolby B system used in cassette decks deals with this by only processing high frequencies.
To work properly, the Dolby system must be switched in ON RECORD AND PLAYBACK. If the cassette deck is good quality, has been correctly aligned to the type of tape being used, and the heads are clean, then Dolby B will do its job very well indeed.
The problem is that people just compare the sound on playback. They prefer the brighter sound of Dolby OFF because it compensates in away for dirty heads and poor alignment. Used correctly on record and replay, Dolby works.
Good old Ray!