Mono and stereo sound

Stereophonic sound, or 'stereo' for short, produces two or more audio channels, with the aim of creating a distinctive sound from numerous directions.

Monaural sound, or 'mono' for short, produces just one audio channel. Stereo was developed with the need for it to be compatible with mono tuners.

Many companies via'd to create the stereo protocols for FM radio. The combined system created by Zenith and GE has become the standard in most countries.

So for example, with a two channel hifi system, a mono tuner will only play through the right hand speaker, whereas a stereo tuner will play through the right and left hand speakers.

While stereo sound may be assumed to be a recent development, it's first radio transmission was nearly a hundred years ago. The BBC first broadcast with stereo sound was in 1925.

Stereo may be more aptly described as multi-channel sound. It took numerous years, since it's first transmission on radiowave, for stereo sound to be used in movies and television (1940 for movies and usually the introduction of NICAM for television in Europe).

In reality, stereo sound can also be used in the modern 7.1/5.1 surround sound home cinema sets, with comprise five or more channels. But, in common parlance, stereo sound is usually only referred to as a two channel technology.