What is Stereo - how it works in audio systems

Stereo sound adds a significant margin to the listening experience, enabling listeners to become more immersed in the music or other material being enjoyed.

Stereo Sound Technology Includes:
Stereo - the basics

We all take stereo sound for granted in modern audio systems, but for music lovers and audiophiles, the quest for the perfect listening experience is a never-ending journey.

We yearn for soundscapes that transport us, enveloping us in the richness and depth of every note. And at the heart of this pursuit lies a fundamental principle: stereo sound.

Loudspeakers in a typical living room arranged for stereo listening — Loudspeakers arranged for stereo listening

At one time, monaural or mono systems were all that was available, but now stereo is all pervasive.

What is stereo sound?

Stereo, meaning "solid" in Greek, goes beyond simply playing audio through two speakers.

Stereo is able to provide a far more enticing sound than mono, where everything emanates from a single point. With stereo, instruments, vocals, and even ambient noise find their own distinct positions in the space, creating a sense of realism and immersion.

The traditional approach to stereo is to have two speakers angled to a listener, each laced on the corners of an equilateral triangle.

The concept is that the sound waves coming from the speakers will combine. The relative strengths from the speakers as well as the phases will mean that to the listener, the sounds will appear as if they were between the two speakers.

The Science Behind the Sound

So how does this stereo work? Stereo sound relies on the binaural effect, a natural human phenomenon. Our ears, spaced slightly apart, perceive sounds differently based on their direction.

A sound originating to the left will reach your left ear slightly sooner, i.e. a phase difference and louder than your right ear, and vice versa.

The brain interprets these subtle differences, pinpointing the sound's location in the auditory landscape.

The basic concept of stereo recording sis that they captures sound through two separate microphones, which mimics the natural positioning of our ears.

These recordings are then encoded into two channels, left and right, which are played back through corresponding speakers.

This results in a faithful recreation of the original scene, where instruments and voices occupy distinct positions in the stereo panorama, just as they would in the real world. As a result it gives a far more engaging representation of the sound than a single monaural system where the sound would emanate from a single point.

In many scenarios including orchestral recordings, studio recordings and the like, many microphones are used and they different channels are mixed into the final two channels.

The proportions and phases of the signals from the different microphones are balanced to give the required positioning within the soundscape required for the recording.

To enjoy the full benefits of stereo, it is best to use loudspeakers - these are typically placed in front of the listener, and as a result the image of the sounds appears to come from in front of the listener as if the orchestra, band, etc was between the two speakers.

Ideal arrangement for listening to stereo sound using loudspeakers

Listening on headphones can also be achieved in stereo, and in fact most headphones, earphones, and ear-pods these days are designed to be used as a stereo pair. However, as the earphones are either side of the head, the stereo image appears between them. It is only a two dimensional soundscape.

That said, with modern processing techniques, it is possible to change the stereo image to appear as though it is coming from a three dimensional soundscape, making listening very engaging.

The Evolution of Stereo

The technology behind producing stereo recordings has evolved over many years, and it is still advancing to this day.

The concept of stereo started with humble beginnings in the late 19th century with rudimentary binaural recordings and it has developed over many years to provide the sophisticated digital formats of today.

Key milestones in this journey include:

1881: The invention of the telephone by Alexander Graham Bell (and others) was one of the pivotal advances as it showed how audio could be transmitted over wires.
1933: Alan Blumlein, a British engineer, developed the first practical stereo recording system, paving the way for commercialisation.
1948: Columbia Records introduced the first long-playing, LP record, which, with a rotational speed of 33⅓ rpm (revolutions per minute) and used very fine grooves to give up to 25 minutes of playing time per side (in those days). Shortly after this RCA Corporation under the Victor label introduced the 45 rpm disc to carry singles. Both these developments set in place the recoding of music on a much wider scale which would lead to a demand for stereo records.
November 1957: The first mass produced vinyl stereo long playing record, LP was introduced by the small Audio Fidelity Records label r
1970s: The rise of cassette tapes and later, CDs, further democratised stereo sound and made it accessible to a wider audience.

The Impact of Stereo

The influence of stereo sound extends far beyond the realm of music. It has transformed the way we experience movies, television, and even video games.

it provides the ability to place sounds in specific locations within the sound space and as a result it adds a layer of realism and depth that enhances storytelling and immerses viewers in the narrative.

Although stereo can be made to sound very dramatic with films or movies where a space ship may roar as it passes by, in reality, the sound from stereo used in music may seem to be less dramatic, but in reality will add more pleasure to the listening experience.

Nowadays we have come to expect stereo sound in everything from small portable radios and wireless speakers.

It must be said that the effect of stereo on small units is much less than that experienced using headphones, or better still, properly spaced loudspeakers.

Choosing the Right Stereo System

For the audiophile, building the perfect stereo system can be an enjoyable and rewarding endeavour.

There are many factors to consider, from speaker placement and room acoustics to the choice of amplifier and audio sources. However, the journey is very rewarding when the system is set up, it is working well, and the music can be enjoyed.

There are some key considerations to selecting the best stereo audio system:

Speakers: The heart and soul of any stereo system, speakers come in various sizes, configurations, and price points. Floor standing speakers offer the best sound quality but require more space, while bookshelf speakers are more compact but may not deliver the same level of bass. Consider your budget, listening space, and preferred sound signature when making your choice.
Amplifier: The amplifier provides the power to drive your speakers and plays a crucial role in shaping the sound. Choose an amplifier with sufficient wattage to match the impedance of your speakers and consider features like built-in DAC (digital-to-analog converter) for improved audio quality.
Audio sources: From vinyl turntables and CD players to streaming services and digital music libraries, the options for audio sources are vast. Choose sources that offer high-quality audio formats like FLAC or WAV for the best listening experience.
Speaker placement: The positioning of your speakers significantly impacts the soundstage and overall audio quality. It is well worth experimenting with the positioning of the speakers to obtain the best stereo experience. Although this is governed by the room, sometimes small changes in position can make an appreciable difference.

Selecting the right stereo system has a number of limitations - the budget and the room in which the system will be used. Often these are a compromise, but by looking at what can be used and how best to use the available resources, a very good system can normally be selected and installed.

Stereo adds significantly to the listening experience, adding a significant degree of reality to the sound, and when listening to music or when watching movies alongside stereo sound the effects can be dramatic and well worth the investment.