The evolution of sound and its impact on design

Think back to the days of old radio broadcasts. Sound was heard from one direction, and the purpose was to convey information. This was the world of monaural. Monaural is made up of a single channel of audio signals, and all sounds are concentrated in the center, so the position or depth of the sound source cannot be expressed. It is simple and low-cost, and is still used today in situations where the main purpose is to "transmit information," such as telephone calls and general broadcasts.

However, in the world of music and movies, a sense of realism is required. This is where stereo came into being. Stereo uses two audio channels (left and right) and expresses the direction and distance of the sound through the difference in volume and time difference (phase difference). This allows listeners to perceive the sound as coming from the right or as having depth.

Further advances in technology have led to the emergence of surround and 3D audio, which replicate the characteristics of human hearing and enable experiences that make you feel like you're actually there in a movie theater or in VR. Behind these advances lies the pursuit of spatial expression. It's important to understand the difference between these two concepts as it will determine the quality of your acoustic design.

If speaker placement and audio processing such as DSP are not appropriate, sound positioning will be disrupted and the sound field will be unnatural. When developing products such as in-car audio, smart speakers, and headphones, it is essential to understand the basics of mono and stereo and achieve appropriate audio processing.

What is mono?

Mono is the most basic format in the world of acoustics. It consists of a single channel audio signal, with all sounds combined into one. Because the same sound is reproduced from speakers or earphones, it does not contain spatial information such as the position or depth of the sound source. This simple mechanism was important as the starting point of acoustic technology.

In the days when radio and telephones became widespread, what was required was not a sense of realism, but the accurate delivery of information. Monaural was ideal for this purpose, with a simple structure and low cost, and was widely used. Even today, mono is the audio of choice when the primary purpose is to transmit information, such as for telephone calls, business announcements, and in-house broadcasts. While it is not suitable for applications that emphasize the "experience" such as music or movies, it is indispensable in situations where simple and reliable audio reproduction is required.

What is stereo?

Stereo is an audio system that has dramatically changed the way we experience music and movies. It consists of two-channel (left and right) audio signals, and by playing different sounds from the left and right speakers, we can sense the direction and distance of the sound. This is the beginning of "spatial expression." The emergence of stereo was a result of a change in the way we enjoy music.

There is now a demand for a "sense of realism" in music and movies, as if you were actually there. Stereo uses left and right volume differences and time differences (phase differences) to position sound front to back and left to right, giving the listener a sense of spaciousness and depth. Stereo is now the standard for most audio equipment. It is an essential method for enjoying music and videos, including home speakers, headphones, and car audio. Furthermore, stereo-based technologies continue to evolve, leading to next-generation audio experiences such as surround sound and 3D audio.

Fundamentals for designing spatial expression

The appeal of stereo lies in the "spatial expression" that gives a sense of sound breadth and depth. However, to maximize this effect, several points must be considered during the design stage.

■ The importance of speaker placement
Since stereo expresses positioning by the difference between the left and right channels, the position of the speakers is extremely important.
・The left and right speakers are placed symmetrically around the listener
・By ensuring an appropriate distance and adjusting the angle, the positioning becomes stable.
If the placement is improper, the sound will be biased or the center position will be lost.

■ Factors that determine the spread of the sound field
・Reflections: Sound reflected from walls and ceilings affects sound positioning
・Distance: The distance between the speakers affects the sense of spaciousness
・Phase: The timing difference between the left and right signals creates a sense of depth
If these factors are not taken into consideration, the sound field will sound unnatural and the sense of realism will be lost.

■ DSP correction and enhancement
In recent years, it has become common to use DSP (digital signal processing) in addition to physical placement to correct and expand the sound field.
・Virtual Surround: Reproduces spaciousness with fewer speakers
- Room correction: Corrects reflections and phase shifts
・3D Audio: Reproduces human hearing characteristics to enhance immersion
These technologies are essential for creating a sense of realism in limited spaces, such as in-car audio, smart speakers, and headphones.

Related Information

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