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A Listener's Guide to Dolby Pro Logic II

A Listener's Guide To Pro Logic II
Almost everyone has experienced the enveloping, electrifying effect of 5.1-channel surround sound in the cinema and at home. Surround sound is addictive. Once you get used to it, you'll never want to go back to plain stereo sound. And now you don't have to.

Pro Logic II from Dolby Laboratories gives you multichannel surround sound from any stereo source—CDs, tapes, videocassettes, TV broadcasts, AAC files, you name it. No matter if you're listening to Stravinsky, the Stones, or a Schwarzenegger movie, you'll get the realistic, involving sound you'd expect from a 5.1-channel system.

How Pro Logic II Works

Pro Logic II is a dramatically improved, updated matrix surround system, based on the principles used to develop the original Dolby Pro Logic decoding back in the 1980s. The original Pro Logic features four channels—front left, center, and front right, plus a mono surround channel that's usually split between two rear speakers. The surround channel is also "band-limited," reducing the treble frequencies. Pro Logic II further enhances the sound with a full-range stereo surround output and a greatly improved steering logic, resulting in high channel separation and an exceptionally stable soundfield.

Figure 1
Pro Logic II offers expanded surround capabilities.

Simpler Circuits, Cleaner Sound

Many surround sound processors have attempted to improve on Pro Logic by adding increasingly complex detection, steering, and decorrelation circuits. Not only do these circuits usually produce unnatural effects, but they can also degrade the sound by running audio signals through additional processing circuits. Pro Logic II strips away most of this processing, instead relying on simple but highly effective servo circuits to derive the output channels. You can hear the same detail and subtlety you experience from your stereo music system—but in full surround sound.

Pro Logic II is not like the synthetic "hall," "jazz club," and "stadium" DSP modes found on many A/V receivers. It adds no reverb, no tonal colorations, and no delay-induced echoes. Instead, Pro Logic II naturally extracts all of the ambience and directionality that already exists in the recording.

Pro Logic II–for Movies and Music

All Pro Logic II receivers offer a Movie mode optimized for movies or programs with Dolby Surround soundtracks. This mode is also appropriate for use with video games. Movie mode retains the important features of Pro Logic, but with a full-bandwidth stereo surround output, the listening experience is much closer to the sound you get from Dolby Digital.

Probably the most innovative feature incorporated in most receivers is the Music mode, which creates a rich and enveloping surround ambience from stereo sources such as CDs.

In Music mode, most systems also include three new controls to fine-tune the soundfield. Center Width allows you to gradually spread the center channel sound into the front left and right speakers. At its widest setting, all the sound from the center is mixed into the left and right. This control may help achieve a more spacious sound or a better blend of the front image.

Panorama wraps the sound of the front left and right speakers around you for an exciting perspective. There's also Dimension, which adjusts the front/back balance to suit your taste.

An optional Matrix mode can be included to produce surround sound from mono material.

Figure 2
Pro Logic II receivers operate in two modes.

What Do I Need to Get Pro Logic II?

All you need is a Pro Logic II receiver or processor and five speakers (plus a subwoofer, if you wish). Since Pro Logic II gives you full-range sound in the front and rear speakers, good quality speakers all around give the best performance. Speaker systems tailored for Dolby Digital are ideal for Pro Logic II.

Figure 3
Pro Logic II system with left, center, right, left surround, right surround, and optional subwoofer.

How Do I Set Up a Pro Logic II System?

A Pro Logic II system is set up just like the original Pro Logic system or a Dolby Digital system. Simply tell the receiver if you're using large or small speakers (if this option is offered), and then balance the channel levels using the decoder's test tone.

Pro Logic II in the Car

Pro Logic II's natural surround sound makes it perfect for use in car audio systems. Whether you're listening to FM radio, digital radio, cassette, CD, or downloaded digital music files, Pro Logic II's five channels wrap you in sound as you drive.

Figure 4
Placement of Pro Logic II speakers in an automobile.

With Pro Logic II in the car, manufacturers can add a center speaker to provide a solid, natural-sounding center image for both front-seat passengers. You get a sound that's more like a stage full of musicians sitting in front of you, instead of hearing only the speaker next to you, as you would with most car audio systems.

If the car includes Pro Logic II's controls for Center Width, Dimension, and Panorama, you can optimize the sound specifically for your car, your music, and your taste.

Pro Logic II is available in standalone processors that can be added to existing car audio systems, or as a feature built into OEM and aftermarket car audio systems.

Pro Logic II brings all of your old audio software into the 21st century, giving you many of the benefits of Dolby Digital from ordinary stereo software. With its elegantly simple circuitry and the smoothest steering logic ever, it's a very rare processor indeed—the kind you'll want to leave on all the time, so you can always enjoy surround sound, no matter what the source.

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