Intro to Receivers page 2

Greg Gentry

Surround Yourself with the Force

One of the primary factors in achieving a home theater atmosphere is surround sound. This auditory effect provided added depth and a sense of realism not heard from traditional two-channel stereo by making the sound seem like it’s coming from all around you. Planes pass dramatically over your head and trains surge by as if they were running though your living room.

Dolby surround was introduced for the home starting in the 1080s to early 1990s as an outgrowth of the sound heard at the movies. Ever since Star Wars was released in 1977, most movies have been released in Dolby Stereo. Thus, their VHS and laserdisc counterparts automatically included the signal. It just needed to be decoded. Initially, decoders were sold separately, and then later became a standard feature on all home theater receivers. However, a by-product of the decoded Dolby was that the dialogue became muddled.

Dolby Surround was further improved, and became what we know today as Dolby Pro Logic. Now, certain sounds and dialogue are directed to specific speakers and the muddled dialogue has been clarified. And, instead of having to purchase a separate component to decode Dolby Surround, Dolby Pro Logic is featured in most home theater receivers.

The THX Ticket

As good as Dolby Pro Logic has been, LucasFilm – of Star Wars series giant George Lucas – felt that it could be improved upon. Therefore, Home THX was born. THX processing is used to enhance the total aural experience. Home THX is based on the belief that home audio components do not accurately reproduce multi-channel film sources. Home THX corrects errors caused in the translation of sound from large theaters into smaller rooms. Home theater receivers with Home THX effectively restore a film’s sound field to match what the director intended you to hear in the movie theater.

There are two versions: THX Select (on low-end and mid-line receivers) and THX Ultra (on high-end units). There is some difference in the quality of final sound between THX Select and Ultra, but not much. The main difference most consumers will find is cost.

The Next Level: Digital Surround

The latest incarnation of multi-channel surround, which features six independent channels of sound – digital 5.1 surround – arrived a few years ago. It features five full-frequency independent audio channels (front left, front right, center, right surround, left surround) plus a separate .1 channel, for low frequency bass effects (directed to your subwoofer).

One of the first things that you hear with digital 5.1 surround is that the side or rear surround speakers are now in stereo (versus mono with Pro Logic). Sound, music, dialogue, and effects are now directed to their proper placement in terms of screen location. If you felt that Dolby Pro Logic sounded realistic, digital 5.1 puts you in the co-pilot’s seat of Luke Skywalker’s X-Wing fighter. Digital 5.1 surround is the most realistic surround currently available.

While there have been other surround sound formats presented in movie theaters, such as Sony’s SDDS, there are currently only two schemes available that will provide you with digital 5.1 surround for the home: Dolby Digital (formerly called AC-3) and DTS, which was created for the movies by MCA/Universal and Steven Speilberg. Both configurations deliver a superb surround sound experience. All DVDs and most laserdiscs released today included Dolby Digital soundtrack, and several DVD and laserdisc titles have recently been released with DTS. Some upscale receivers feature auto-sensing circuitry that, upon sensing a Dolby Digital or a DTS signal, switch to the proper processor for decoding and playback.

Intuitive Technology

Since its introduction in 1995, most home theater receivers now include a built-in Dolby Digital decoder. They will usually include Dolby Pro Logic and then have the ability to upgrade to digital 5.1 manually. These receivers have the six separate channel input jacks – front left, front right, center, right surround, left surround, and low frequency effect – for the processing of the 5.1 channel information. Having a separate input for each channel ensures that the correct sound information is piped to the proper channel. The procedure for using DTS technology used the same setup. Some higher-end receivers avoid the whole idea of individual channel jacks.

Sort of Surround Sound

Not all movies and music discs are encoded in Dolby Pro Logic, Dolby Digital, or DTS. So, most equipment manufacturers offer artificial sound modes such as “hall,” “matrix,” or “simulated.” These modes can add a touch of dramatic realism to this material. Such effects can also be employed in the playback of CDs, giving them some of the added depth and the feeling that true surround sound gives you.

Internal Equalizers

At one time, equalizers were utilized to help shape the sound in audio systems. Today, most home theater receivers include DSP (Digital Signal Processing) to help shape the sound even further.

Essentially, DSP carries equalization of sound into the digital domain. DSP allows the listener to customize their listening environment to their own specific desires. It also re-creates the acoustics possible, bringing to life such real-world listening environments as “concert hall,” “jazz club,” “movie theater,” and so on. Most manufacturers include various DSP setting to simulate acoustics, ambience, and reverberation. These modes are artificial settings, but can add a depth of realism to your listening experience. While these settings have predetermined delay times, some models allow you to adjust the reverberation to suit the acoustics of the room, or your personal preference (called variable or adjustable delay). While this feature does add to the cost of the receiver, it offers more versatility overall.

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