Stereo sound

The word stereo is derived from the Greek word stereos = "solid". The second word, phone = "sound".
In early years, the term stereophonic sound was used more, it could be seen on records with the information that it could also be played with monophonic cartridges.

Attempts to explore and experiment with stereo sound were already made in the beginning of the 20th century, in broadcasting, film and . The modern use of commonly used stereo began in 1958 when the first group of stereo two-channel records were issued. In the late 50s, broadcasting was made in USA with AM and FM at the same time to be used with "Simulcast" receivers, designed for the purpose. HH.Scott was one manufacturer that implied simulcast technology in their FM tuners. In 1961 the first commercial multiplex FM stero tuner were made by HH-Scott, the 350 model.

Compared to dolby surround systems etc with more channels, sound system with at least 2 channels, may reproduce positioning of the original sound, and a feeling of space perception of the recorded sound. Of course, such a stereo space effect can also be simulated as in a multi track studio recording.

Sound localization

We know that sound in air has a certain speed, around 340m/s. The perception of sound localization and distance relates to time differences between left and right, and the character of the reflections. If a sound comes from left, it first reaches the left ear but the sound to the right ear must be reflected in a way to reach the right ear which is shadowed from the left audio source.
Since the right ear is directed more to the right and because of the shape that acoustically forms a directional pattern, the sound that is heard in the right ear comes from reflections with added delay. With that delay, a difference in localization is perceived.