¿Por qué mi coche tiene sonido envolvente?

Si alguna vez ha estado en una sala de cine, probablemente haya experimentado lo que se conoce como sonido envolvente. Hay al menos cinco pistas de audio discretas codificadas en la película que está viendo, y la mayoría también incluye un canal de efectos de baja frecuencia (LFE). El propósito de estos canales de audio es permitir que la fuente de cada sonido se dirija a una ubicación particular en el cine para que todos puedan disfrutar de una experiencia realista, sin importar dónde estén sentados.

Esto es lo que ha provocado la introducción del procesamiento de sonido envolvente en el mundo del automóvil. Es relativamente fácil para un diseñador de sistemas de audio configurar una experiencia auditiva realista desde una sola posición de escucha usando ecualización, ajuste preciso del nivel de salida y retardo de la señal. Incluso cuando te sientas mucho más cerca de un altavoz, una afinación cuidadosa puede hacer que la música parezca provenir de un conjunto de altavoces imaginarios en todo el escenario de sonido.

El escenario delantero

Para los entusiastas del audio móvil, gran parte de nuestros esfuerzos en el diseño y ajuste del sistema se dedican a la creación del escenario frontal. Este término describe los altavoces que están instalados frente a nosotros y sus ubicaciones. Podemos usar el procesamiento de señales para ajustar la salida de cada altavoz para que la música suene como si viniera del centro del tablero, aunque esté sentado en el lado izquierdo del vehículo. El problema con estos ajustes es que solo funcionan para una ubicación de asiento. El pasajero a menudo sufre con una respuesta de frecuencia menos que ideal y la mayor parte de la música parece emanar del lado derecho del tablero. Para el realismo, esto es menos que ideal.

Tecnología de control de sonido

La mayoría de las salas de cine tienen parlantes dedicados a la izquierda, al centro y a la derecha detrás de la pantalla principal. Incluir el canal central le permite al productor de audio fijar la posición de las voces y los efectos en una ubicación específica en relación con la pantalla. Si alguien está siendo entrevistado y está centrado en la imagen, lo más probable es que su voz sea reproducida únicamente por el altavoz central. If they move across the picture, the level of their voice decreases in the center and increases in one of the left or right speakers relative to their position. Even if you are sitting on the far right side of the theatre, voices and sounds are steered for incredible realism.

Surround Sound in Cars and Trucks

Think about how well the ability to steer sound works in a theater when you are in a less-than-ideal seating position. Now think about your vehicle. You are sitting much closer to the left-side speakers. You will hear sound from them before anything from the right speakers, and those sounds will be louder. Your music will seem to come from the door or left side of the dash.

By including a center channel in the middle of the dash, the system designer can route audio signals that are equal in amplitude in both left and right channels to the center speaker. To improve the accuracy of the system a step further, those signals are also removed from the left and right speakers. The result is a system that reproduces music evenly across the dash from both the left and right seat. Music sounds great from the back seats as well.

Rear and Side Speakers

In our movie theater, the rear or side speakers are primarily used for special effects. A helicopter or plane flying into the scene from behind us is a good example. In modern movie production, that information is hardcoded into the surround channels.

Because we are only listening to two-channel audio (left and right) in our vehicles, there is no opportunity for the music producers to direct specific sounds to rear channels. However, complex signal processors from companies like Bose and Harman do an excellent job of extracting audio information that is suitable for the rear speakers. Sophisticated algorithms can also produce an increased sense of soundstage width in systems with speakers in the rear doors. Rear deck speakers add a sense of ambiance and room size to the performance. How they analyze the relative phase and amplitude of signals within the stereo recording is simply amazing. So, too, are the results of their efforts. Your music can appear to come from spaces beyond the boundaries of your vehicle.

Mix it Up

OK, we admit that the title of this article is click bait. We are talking about upmixers here. An upmixer, by definition, takes a number of audio channels (in our case, two) and turns them into a greater number of channels (usually six). If we feed an upmixer left and right signals, it can generate left, center, right, left rear, right rear and subwoofer output signals. Some upmixers provide eight channels:left, center, right, left side, right side, left rear, right rear and subwoofer. Many OEM systems use these 7.1 systems with great success!

You sold me! Gimme, Gimme, Gimme!

When it comes to the aftermarket, the options for upmixers are limited. Some people have mucked around with using computers or tablets with external sound cards, but the interface is clunky and frustrating. On top of that, you don’t get a radio tuner, there is no backup camera input and you can’t add SiriusXM. Tablets look cool, but they are not ideal for use in vehicles.

The Alpine PXA-H800 processor (and companion RUX-C800 controller) includes Dolby Digital, Dolby Pro Logic II and DTS Digital Surround decoding. This processor will generate a genuine center channel signal with audio information that is removed from the left and right channels.

Audiofrog hasn’t been shy about the fact that they are working on a new signal processor that is specifically designed to create a realistic center channel and surround channels. The solution is called Multiseat Stereo. Unlike most systems that use versions of DTS or Dolby Digital, Audiofrog has partnered with PerfectSurround to create a system that is free from phase artifacts.

Confused? Don’t be. In a nutshell, PerfectSurround does a better job of steering sound than other processing systems. The results are more realistic and provide better bass focus in the front of the vehicle. There is no firm release date as yet, due to patent applications and all that business stuff, but keep your eyes peeled.

The Future of Great Mobile Audio for Everyone

If you and your co-pilot both love great car audio, then a mobile sound system with a correctly processed center channel is an easy way for both of you to enjoy a realistic performance from any position in the vehicle. If your car or truck came with a surround sound system, visit your local mobile enhancement retailer to find out how they can upgrade it with better speakers, more power and tuning that matches your listening preferences.

If you are designing a new system, then keep an eye out for new processors to arrive on the market. The future of mobile entertainment that sounds realistic for everyone in the vehicle will be based on upmixers.