Basic knowledge of acoustics - a brief discussion on stereo

Basic knowledge of acoustics - a brief discussion of stereo

Concept of stereo

Stereo is a system composed of two or more sound transmission devices, transmission channels and speakers (speakers, headphones). After appropriate system layout and adjustment, the spatial distribution of hearing perception on the scene is obtained, which we call stereo.

Everyone has two ears. In a monophonic sound reinforcement system, we can hear the spatial distribution and orientation of the sound position, which is what we call binaural effect. The binaural effect is the effect that people rely on the volume difference, time difference and timbre difference between the two ears to judge the direction of the sound. When the sound is different in strength, the distance between the sound source and the listener can be felt.

For example, when we are broadcasting a band performance, if we use a recording device to record the sound (or use several pickups and mix them together) and amplify it through one channel and then play it out from one or a group of speakers, this is a monophonic system

As shown in Figure 1-8 a At this time, since all sounds are emitted from the same speaker, the original sense of space (especially the sense of spatial distribution of the sound group) also disappears. This kind of playback is called monophonic. If the entire system from recording to playback can restore the original sense of space to a certain extent (it is impossible to restore it completely), then this kind of playback sound with a certain degree of spatial distribution characteristics such as azimuth and level is called stereo in audio technology. As shown in Figure 1-8 b

Compared with dual-channel and mono, it is not only the difference in spatial distribution positioning, but also the restoration of the original spatial distribution of sound. When the mono tracks are recorded and amplified separately, the sound quality of stereo will be greatly improved compared to mono, and the sense of presence will be enhanced. However, there are still some differences between dual-channel stereo and multi-channel stereo, four-channel, and surround stereo. For example, the 5.1 stereo channel in the figure below, the surround sound of the cinema, etc.

So is it better to have more channels? Not really. In fact, as long as the speakers with the same height of the instruments and the same height of the human ears in the original actual performance venue are used, a very good listening and viewing experience can be obtained. It is like we used to use center speakers frequently but now rarely see them, because the stereo effect of two left and right channels is already very good. As for general performance venues, two sets of line arrays are generally used to solve the problem.

In addition to the three subjective sensations of loudness, timbre, and pitch (frequency), human ears also have the ability to locate sounds. This ability is due to the time difference between the distances between the two ears and the difference in sound pressure levels.