Digital Trends

Introduction

Now that home theaters and home entertainment centers seem to be here to stay, I guess it is safe to say that the old fashion single speaker televisions are relegated to the museum. As such, it appears to be the right time to examine the plethora of audio options and different audio formats that have moved from the theaters into our homes. Most of us now have speakers placed all over the room and with the newer formats coming out even more speakers are on the horizon. We have turned over the design of our living rooms to these speakers and center our lives over the best position to listen to the sounds from our favorite films and television shows. Even the modest speakers found in our home computers have given way to speaker arrays surrounding our desks. So sit back, grab a cup of coffee and let's run through the various audio formats common to those little boxes next to our television sets.

Mono

The most basic sound format would logically be monaural, simple one channel sound. Well, forget logic here, true mono sound is extremely rare in home theater today, most of the time the receiver will actually provide two channel mono if it detects a mono audio source. Rather than just pumping the sound through the center speaker a typical home theater receiver will split the signal equally and send it to the front speaker pair. This provides a somewhat fuller sound field for the listener. So, technically modern mono sound is better placed with Dolby audio than anywhere else.

PCM

Next in line is pulse code modulation or PCM. This is a defined standard set for DVDs but its not always found on all discs. It provides a two channel audio and is found primarily on DVDs mastered from older two channel sources, especially concerts and transfers of records. Basically the way this format works is the nice smooth sine wave curve of sound is sampled, the amplitude and frequency at a particular moment in time is recorded digitally. Older PCM standards allow for the amplitude to be broken down into five ranges. The current pulse is assigned the nearest value when sampled. Currently, this has been expanded to a ten value range providing for a much truer reproduction.

Prologic

Now we come to Prologic. This is a method devised by Dolby labs to provide a feel of surround sound from a two channel source. The rear speakers actually are mono that is they have the same information sent to the rear left and rear right but when heard in conjunction with the front speakers and considering the room is rarely symmetrical, the effect is you hear a rather full rear audio field. With more and more people using computers and portable DVD players to enjoy DVD and other programming, Dolby Laboratories has come up with advancements on their standard Prologic. The new system is called Prologic 2 (Prologic II). With this system there is an enhanced feeling of a true surround field utilizing as few as two speakers. There are two modes for Prologic 2 Virtual Speaker, Reference Mode where the distance between the front speakers sets the distance for the two virtual rear speakers. Then there is Wide Mode where the virtual rear speakers will appear to be farther apart creating a fuller sound stage in your listening area.