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What is Stereo Sound? – A Realistic Experience!

Have you ever wondered why the music you listen to everyday, sounds realistic? It is as if you were sitting in a room, listening to your favourite band play live, right in front of your eyes. This aspect of sound reproduction, is something that every audio engineer should understand. Hence, if you aspire to be one yourself, ask this – What is Stereo Sound?

The subject for today’s article is something that resonates with many audio enthusiasts and practitioners. But not too many of them are aware of the guiding principles behind the concept of stereo audio. You will learn more about the various methods of achieving the stereo effect, and how listeners are affected by them. Are you curious to know? Me too!

Introduction – Stereo? How?

Otherwise known as “stereophonic sound”, stereo is a sound reproduction method that produces the illusion of sound coming from multiple directions. This is done by using two or more discrete audio channels through a configuration of two or more loudspeakers (or stereo headphones) to re-create “natural hearing” (the impression of sound heard from various directions).

Stereophonic Sound

The main diagram shows how stereo sound works in nature, and the inset-image shows the electronic simulation / Photo by RIT RAJARSHI / CC BY-SA 4.0

The term “stereophonic” does not only apply to the common two-channel, two-speaker systems, but also to “surround-sound” systems as well. It is different from monophonic (mono) sound, where audio is perceived to come from one position, often centered in the sound field (similar to a visual field). Stereo sound is widely used in broadcast radio and TV, recorded music and the cinema.

Here are the topics that we will be covering today:

  • Types of stereo sound
  • Recording applications
  • Common usage

Types of Stereo Sound

There are two forms of stereo system and the first one is called “natural” or true stereo. This is where a live sound performance is recorded by an array of microphones. Thus, any natural reverberation or ambience present, will also be captured by the mics. The signal will then be played back through multiple loudspeakers to recreate the live sound experience (as accurately as possible).

Artificial Stereo

A guitar recording into a mono track, before being mixed down to stereo (Artificial Stereo) / Photo by mark sebastian / CC BY-SA 2.0

The second one is called “pan-pot” or artificial stereo. This is where a sound that is recorded on a single-channel (mono) is played back through multiple loudspeakers. When the relative amplitude of the signal sent to each speaker is being attenuated, an artificial sense of direction (based on the listener’s perspective) can be created.

The relative amplitude of the signal can be adjusted by using a control known as a “pan-pot” (panoramic potentiometer). When multiple “pan-potted” mono signals are combined together, a complete, yet entirely artificial, sound field can be produced.

Two-channel Stereo Recording

When recording for two-channel stereo, two microphones (strategically positioned) will record the sound source simultaneously. Both recordings will be similar, but each will have distinct time-of-arrival and sound-pressure-level information. These subtle differences in timing and sound level will be used by the listener’s brain to define the positions of the recorded sounds.

Time Difference

A car travels past a stereo microphone and the file reveals the time difference between left and right / Photo by Sophie means wisdom / CC BY-SA 3.0

Playing stereo recordings on mono sound systems will typically incur significant losses of fidelity. Since the sound is captured by each microphone at a slightly different time, the sound waves will be out of phase. This causes constructive and destructive interference when both tracks are played back on the same speaker (also known as phase cancellation).

Sound Localization

Photo by OpenStax College / CC BY 3.0

Recording Applications

Stereo sound is about creating a perception of location for sound sources (voices, instruments, etc.) within the original recording. Audio engineers typically aim to create a stereo “image” with localization information. When a stereophonic recording is played through stereo speaker systems (rather than headphones), each ear will of course, hear sounds from both speakers.

In most recording situations, the audio engineer will use more than two microphones (in some cases, many more mics are used) and may mix them down to two tracks in ways that highlight the separation of the instruments. This is intentionally done in order to compensate for the mixture that occurs when listening through speakers.

Stereo sound may be hyped to be all about localizing the position of each sound source in space, but this would only truly happen in a carefully engineered system and environment, where speaker placement and room acoustics are seriously considered. Many sound systems, such as home theatres and the like, are not capable of creating a realistic stereo image.

Equilateral Triangle To get the best results when listening to stereo recordings, two identical loudspeakers have to be used, placed in front of and equidistant from the listener, with the listener positioned on a center line between the two speakers. This essentially forms an equilateral triangle, with the angle between the two speakers around 60 degrees as seen from the listener’s point of view.

Common Usage

It is important to take note of the common usage of terms related to stereophonic sound. Essentially, a “stereo” is a two-channel sound reproduction system, and a “stereo recording” is a two-channel recording of any sound source. This can cause some confusion among consumers, since five (or more)-channel home theater systems are not widely advertised as “stereo”.

AB

“AB” stereo recording technique / Photo by Polselekah / CC BY-SA 3.0

Keep in mind that not all audio recordings that are mixed down to two-channels, uses stereo recording techniques in them. Take for example pop music, where recordings are usually done using close miking techniques, which artificially separate signals into discrete tracks (mono). The engineer will then position these individual tracks within the stereo field.

Simple techniques such as “left-right” panning controls, to more sophisticated ones (extensively based on psychoacoustics) such as channel equalization and mid-side processing, are used to adjust the position of the mono tracks in the stereo mix. This process produces little to no resemblance of the actual spatial relationship of the musicians (during the performance).

Orchestra Recording

An orchestra recording in the studio in one complete take / Photo by Jolly Gamer / CC BY 3.0

In reality, it is very common for different tracks of the same song to be recorded at different times and in different studios, before finally being mixed down to a two-channel stereo recording for commercial release. There are exceptions such as classical music, where it is typically recorded in one complete take, thus preserving the realistic spatial relationship of the performers.

We have come to the end of the article. Hopefully by now, you have a decent understanding of stereophonic sound, and how it basically works.

Don’t forget to leave comments or questions below, and share this article with your pals!

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Farhan

When I'm not rocking out to great music, I'd prefer to be sleeping on a field on a windy day =)

8 Comments

  1. Hi Fahran. Your detailed post was an interesting read, even though I am not that into audio technicalities. I have a question for you. I noticed that there are two types of stereo: true and artificial. I wonder which one produces better sound. Do they differ only in production but the end product sounds the same? My question is all messed up, but I think you get the point, thank you for your reply.

    • Hi Nikola!

      You have asked a very good question. Between the two types of stereo, there is no better one. They just sound different. True stereo will give you a more accurate physical representation of the recorded sounds, in relation to the stereo field (for instance, positions of instruments within an orchestra). Artificial stereo is used in genres like pop music, where there is a lot of overdubbing going on during production.

      To sum it up, the recording process and the end product is very different for both types of stereo.

      I hope that clarifies the issue. Thanks for reading!

  2. WOW, this was one of the most fascinating posts about stereo sound. I never knew so much went into constructing and recording sound. In fact, I thought all sound recorded was “artificial” for playback. But you broke it down in that there is natural, pan pot and two channel recording. Equally fascinating is different tracks of the same song might be recorded at different times or even different studios. Now Im thinking about my favorite artists like Beyonce and all that goes into her studio sessions. Amazing.

    • Hi Tiffany!

      Yes, there is much to learn about the technical aspects of any kind of audio production. I’m glad that you have found this article interesting and educational.

      Thanks for dropping by!

  3. Hi Farhan! 🙂

    Very nice post! I know a little bit about sound being a musician singer-songwriter, but I don’t have too too much experience recording. A bit, as I’ve recorded some songs, but not in-depth audio engineer-wise. I knew some of the things you were talking about here, but I also learned some new things, like the “close miking” technique – I’ve never heard that term before, even though I understand the concept. 🙂 Thank you for writing all of this! 🙂
    ~
    Artistically yours,
    Pascal

    • Hi Pascal!

      I started out as a musician myself, before I seriously got involved in audio engineering. Many of the concepts will take time to sink in, but they are worth taking the time to understand, especially if you are into music production. I’m glad that you got something out of it!

      Thanks for reading!

  4. Great information about stereo sound. You really know your stuff.
    Would you say the best way to experience the illusion of the sound coming from multiple directions is by using stereo headphones?
    I say this as I think there would be the least amount of variables from headphones compared to a speaker setup in a room. With a speaker set up you would need to consider things like the type of speaker the distance from the speaker, deflections and reflection of sound off of objects in the room.

    Enjoy reading your posts Farhan…keep it up!

    • Hey Paul!

      Yep, I would also recommend using headphones for listening to binaural recordings. This is the most hassle-free option that is convenient for most people. However, do take note that headphones too, have their limitations in reproducing binaural audio recordings (as explained in the article).

      Thanks for your thoughts!

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