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Audio technology explained

By , 26 Nov 2012

Audio technology is baffling. That's a fact. Let S21 lead you through the jargon-filled world of Dolby Digital, SRS and 5.1 into a state of audio technology enlightenment.

Mono, Stereo, 5.1, 7.1

Mono sound is single-channel sound from a single loudspeaker. Stereo sound uses two channels and a left and right speaker to give a sense of depth.

5.1 sound uses 6 channels to encode sound for 6 speakers: left, right, centre (usually for voice), two rear speakers and a subwoofer. The subwoofer is a special kind of loudspeaker used to produce low-frequency bass sounds that cannot be recreated by the other speakers. 5.1 sound is used in cinemas and also in DVD & Blu-Ray home cinema systems to provide a "surround sound" effect.

7.1 sound is an extension of 5.1 that uses two additional side speakers to enhance the surround effect, and is starting to replace 5.1 in cinemas.

Dolby - the analogue years

Dolby introduced Dolby Stereo back in the 1970s as a way of providing multi-channel sound for cinemas (most famously in the first Star Wars film). Although the word stereo suggests two speakers, Dolby Stereo actually encodes four channels (centre, left, right and surround) into a two-channel format which can then be decoded to reproduce the original four-channel sound.

Confusingly, Dolby Surround was the name given to two-speaker consumer products based on this technology. The system was used in VHS video recorders and early stereo TVs.

Dolby Pro Logic is a more advanced version using the same logic system found in professional Dolby Stereo systems and able to decode the full four-channel sound.

The original Dolby Stereo system included Dolby A type noise reduction. Dolby SR noise reduction was introduced in the 1990s as a replacement for this system, and is still used today when digital audio is not available.

Dolby Digital

Dolby Digital is a modern standard used for Blu-Ray, HDTV broadcast, etc. Dolby Digital is a digital encoding of 5.1 (six-channel) sound.

Dolby Digital EX is an extension of Dolby Digital, used for 7.1 sound systems.

Dolby Digital Surround EX is a version of Dolby Digital EX used in cinemas.

Dolby Digital Plus is an extension of Dolby Digital with support for increased bitrates and more audio channels.

Dolby TrueHD is a lossless encoding with support for up to 14 channels. It's available in some Blu-Ray systems.


Whilst Dolby Digital is a standard for encoding multi-channel audio, SRS is a set of technologies used to make stereo speakers sound more like surround sound systems. Since a TV cannot provide a genuine surround sound experience, technologies like SRS TheaterSound, SRS TruSurround HD and SRS Wow HD are used to "trick" the mind into thinking that the sound is "bigger" than a 2.1 or stereo speaker system can produce. The result is claimed to be a richer sound with clearer dialogue and room-filling effects.

Think of it this way: no matter how many speakers you have, you still only have two ears. Sounds from the speakers reach the ears by different routes - directly or by bouncing off walls. The brain processes all of this and recreates a sense of sound in 3D. By fiddling with frequencies and timings, SRS technologies aim to trick the brain into thinking that the sound is coming from all around.

Some people prefer the sound from an SRS system; many cannot tell the difference; some actively dislike it. If you don't like it you can turn it off.

Dolby Virtual Speaker

Dolby Virtual Speaker is another system that aims to create realistic 5.1 surround sound from just two speakers.

What you need to know

If you're still confused (or perhaps even more confused than before), I'll keep this bit simple. Almost any modern TV, Blu-Ray or DVD system you buy will support Dolby Digital. Most TVs also support some kind of virtual surround too (SRS or Dolby Virtual Speaker). So don't worry about the specs.

If you want to improve the audio quality of your TV, the simplest way is to add a sound bar with SRS or Dolby Virtual Speaker support. If you can afford it and have the space, go for a 5.1 home cinema system.

There, it was simple after all.

User questions

Sorry - questions and comments on this page are now closed.

How does it connect with a flash drive?

Asked by Shawn from Usa on 20th Jul 2017

I have a LG flat screen TV, 32", with TruSurround, but wanted to improve that with a Soundbar and woofer. I can't get the tv to play the sound through the LG LAS350B system. What am I doing wrong? Please.

Asked by Lester from Scotland on 23rd Feb 2016
The Soundbar is connected to the TV via an optical cable as I was advised.
However, I thought the cable should pop in to each of the sockets but it just seems to sit in them. Is that correct? Read on.
The remote controller for the Soundbar seems to work by changing the readout on the Soundbar text screen, volumes etc, but I don't get any sound out of it or the woofer. That is definitely wired correctly.
I have tried to disable the TVs speakers but that doesn't seem to achieve anything. The sound disappeared but the Soundbar did not kick in as I hoped.
I can't find an 'external' speaker command in the technical settings under 'audio' menu on the tv.
Could the TV be too old. It looks as though was made in 2009, but has two HDMI ports, a LAN port, an optical port and a PCMCIA port.

Reply by S21 from UK on 24th Feb 2016
Lester, optical cables are not the easiest type of connection to plug in. They need to be pushed in all the way, and sometimes there is a flap that has to be pushed out of the way.

User comments

Sorry - reviews and comments on this page are now closed.