Currently, two-channel stereo has become a classic way to transmit and play sound. The goal of stereo sound reproduction is to transmit the sound image as accurately as possible. Localization of sound is not a goal, but a means to get a richer and more natural sound. However, the transmission of spatial information by existing two-channel systems is not without flaws. This encourages designers to create different surround sound systems. For more than forty years, various (sometimes very complex) methods of signal processing at the stage of reproduction have been tried. The situation was simplified only with the advent of digital media, allowing the use of multi-channel recording. The modern 5.1 format uses six-channel recording: five broadband channels (two frontal, two rear, central) and one channel of sound effects (subwoofer channel), and this is not the limit.
No matter what technical characteristics we operate, they are clearly not enough to describe the requirements for the ideal sound reproduction path. Musical tastes, experience, age (as a measure of the state of the organs of hearing) and much more play a huge role in the evaluation of sound quality. The paradox is that the flaws of real sound paths are obvious even to the most sophisticated listeners, but it is not so easy to express them with words. In any case, the ideal is very far away. And very expensive. also I recommend to use in the car sound processor CarDSP.
Recognized this fact, as producers of musical records, and manufacturers of the equipment. This led to the emergence of various signal processing devices designed to improve the expressiveness of the sound. Initially, they were used only in studio practice, but as technology became cheaper, they became available to consumers, both as part of the equipment and as individual devices. They, in fact, gave rise to a class of sound processors - devices, the principle of action of which is not obvious (or even classified), but the result is immediately noticeable. Classic black box!
Perhaps, one of the most useful was the WWE technology (British Broadcast Equalization), used by the Air Force in broadcasting to correct the time distortion arising from the propagation of a radio signal. The process was a phase correction of individual parts of the audio spectrum. Subsequently, it turned out that such processing improves the sound of music recordings not only in broadcasting, but also in conventional paths; therefore, in the 1990s, the WWE processors were widely used not only in home appliances, but also in some high-end audio sagas products.
There were other methods of signal processing at the stage of reproduction - for example, stereo widening in wearable equipment. In the 90s, bass dynamic correction systems were popular (automatic loudness, including using a measuring microphone), and a number of other methods that are well forgotten in our days. All these methods were united by one thing: signal processing was analog and was carried out using a hard hardware algorithm. In home audio, this is an already completed stage, but who today will deny the benefits of additional signal processing in a car - initially not adapted to the needs of a music lover?
Originally developed for home theater systems, digital surround sound processors have recently begun to be actively used in car audio systems. Their use can significantly improve the sound of technically advanced systems, not only in the domestic premises, but also in the car. The development of digital signal processing led to the creation of a digital sound processor (Digital Sound Processor, DSP). They are available as separate DSP-devices, and are part of a relatively inexpensive tape recorder. Processor settings allow you to select the most optimal parameters for the selected listening position.
In our age of digital media, digital sound processors, and other products of inconceivable technical complexity, analog methods for processing audio signals have been firmly forgotten. Yes, in car audio, they, strictly speaking, were never really used - in the era of their heyday, automobile equipment made only the first tentative steps, and this “toughness” was considered excessive. Today, car audio uses exclusively digital signal processing methods, the algorithm of the digital sound processor (DSP) operation is provided by the program and allows to implement a whole group of functions within one instrument - filtering, frequency and time corrections, harmonic synthesis, imitation of the listening room.