Surround Sound

It is a buzz word surrounding wide range of Music Systems today! If you have visited stores to buy a DVD Player or a Home Theatre, you must have seen this label. Some labels doesn’t say “Surround”; you might have seen labels such as Dolby, Dolby Pro logic, DPL II, DTS. These are few of those technologies or logic, that create a theatre effect in home. Of course, theatre is so different from home, in many ways

Now, which creates a good theatre effect?. Which DVD player or Home Theatre is Good, or Best?.

Lets start from basics. What is a Surround Sound?. In the conventional music players, or VCD, VCR, DVD Players, you get stereo sound..(mono is outdated, so lets not discuss that). Stereo means, you will have two channel output; Left and Right. This is good enough, if you are watching some plain TV shows, or anything you recorded using your Digicam /Handy Cam. But, if you are watching movies, obviously, stereo is not sufficient. Time to go Surround!!!. How do you create surround effect?. It should be as simple as surrounding your TV hall with many speakers. But, the problem with that approach is that, all your speakers speak the same sound at the same time. Today’s home theatre systems have just solved these problems by making separate channel outputs, so that, you feel, the event you are watching is happening just in front of you. They simply channelize, left side sounds to left speakers, right side channels to right speakers, rear side sounds to rear speakers …and so..on.

But, technology is not that simple. Just think, how do you know, which sound belongs to front left channel, and which belongs to right rear channel?. And imagine, you are watching a movie, in which a bike moves from left to right. How do you reproduce this effect in your home theatre?. That’s exactly what these Dolby pro logic, DTS and all are doing!. SoundzGood ?.. read on..

Well, the question needs to be still answered as to, how can one differentiate, sounds that belong to different channels?. Yes. It is very difficult, if all these are recorded in only one channel. There are several approaches to reproduce surround effect. Simplest and affordable approach is using several speakers around the listener to play audio coming from different directions. Other approaches are little complex and involve “psychoacoustic sound localization”, “audio hologram”, “Ambisonics reconstruction”, “wave field synthesis” etc.

In the Simple approach,Surround or Home Theatre is a two phase process. First Phase (Encoding)- The audio is recorded from different directions, merged together, and stored on the media (DVD disk) as a single track. Second Phase (Decoding)- Read and separate the channels and output to respective speakers. This second phase is what is called ‘Surround’ logic. Dolby 5.1 , Dolby Pro Logic II, DTS, DTS-ES are few of such technologies.

In home theatres, you might have seen 5.1, 7.1 , 4.1, 6.1. These are actually, the number of output channel, and applies to Decoder and the speaker system. Lets understand the numbering system.

5.1 means, total 6 channels output. 5 surround speakers + 1 Sub woofer. Within the 5 surround speakers, you have 3 front - left (L), Centre (C), Right (R). 2 for rear - left (Ls), Right (Rs) and 1 for Sub woofer. As we saw in my last week’s blog, Subwofer boosts the Low Frequency sounds(10 Hz to 80 Hz). And others are normal speaker (capable of reproducing above 80Hz and above frequency range).

4.1 means Three for speakers at the front - left (L), center (C) and right (R). One for both surround speakers at the rear - mono surround channel (S).

In 6.1 , One Surround Back channel is added to 5.1 setup.

And 7.1 adds two additional rear speakers to 5.1; This is recommended only if your home theatre hall is big enough. Practically speaking, 7.1 improves envelopment of sound where a big space exists between the rear surround speakers. So, only if the space between front and rear speakers is very large (more that 30 feet), 7.1 is better over 5.1

The speaker positioning and the hall acoustics plays very important role to create a real home theatre experience. Acoustics is a big topic in itself; for now, we will stick to the above said standard speaker positioning and move on …

Lets now look into the ‘logic’ labels:

Dolby Digital /AC3 / Dolby 5.1

Developed by Dolby (http://www.dolby.com/). It reproduces high-quality digital audio for up to 5.1 discrete channels (Left/Center/Right/Left surround/Right surround/Low-Frequency Effects). The five speaker channels produce a directional and more realistic effect and the Low- Frequency Effects (LFE) channel (usually reproduced through a subwoofer) can often be felt as well as heard.

Dolby Pro Logic / II

This is really a must have ‘label’, especially Dolby Pro Logic II or DPL-II. This can reproduce 5.1 channel output from Stereo (2 Channel) music. If you see the DPL-II algorithm technical details, It mandates that the Stereo recording is to be done using Dolby Pro Logic II encoder. See what Dolby tells in detail … (you can skip it, if you feel it is too techie stuff)…… During creation, Dolby Pro Logic II and Dolby Surround programs are matrix-encoded onto two audio outputs. They are treated as two-channel or stereo audio throughout the broadcast distribution chain, then decoded back into surround sound by the viewer’s home receiver. Dolby Pro Logic II and Dolby Surround broadcasts perfectly complement the Dolby Digital 5.1 broadcasts available on DTV services. (Check more details)

The Decoder is intelligent, and it splits the stereo channels into 5.1 channels, by analysing the sound intensity shifts and time delays. So, even if the recorded media is not encoded using Dolby Pro Logic II encoder, you can expect the surround effect to be nearly as good as 5.1 surround (AC3)reproduction. What I have observed is, there won’t be very clean isolation between left & right channels. But, front channels and rear channels are clearly isolated. This means, you can play MP3, WMA and WAV files in surround effect!!. So, don’t miss this label!

DTS

Digital Theatre System, developed by DTS Digital Entertainment. (http://www.dts.com/ / http://www.dtsonline.com/). This is a complete digital surround solution. Like Dolby, DTS also has its own Encoding scheme and Decoding scheme. In my opinion, if you have a DVD Player, that has SPDIF output channel (SPDIF is a digital channel, developed by Sony & Philips) and your Home Theatre receiver is DTS enabled. In this case, DTS effect is more close to reality compared to Dolby Digital. You can see a cutthroat competition between Dolby & DTS. Check more details.