The surround sound receiver is at the heart of a home theater system.
If you've read the introduction to surround sound systems already, you will know that I said we needed two main things for an good home cinema sound system - an amplifier and some speakers.
There are two main articles introducing the role of amplifiers in a home cinema system - one is about stereo receivers and the other is about AV receivers (this one).
An AV receiver is used for a surround sound installation, and a stereo receiver for a 2-channel setup.
In this article we will discuss AV amplifiers and receivers - which may also be referred to as a surround sound receiver, a home theater receiver or a surround sound processor.
AV receivers are the 'brain' of any home cinema system.
It is an amplifier that powers the speakers in your home theater setup - but it also does a whole lot more.
It processes the audio and video signals from a range of input devices ( Blu-ray, DVD, cable box etc), and transmits the audio to the speakers and the video to the display.
Now, it can be confusing when talking about the surround sound receiver because, as those of you who are still paying attention will notice, I've already said the AV receiver takes audio and video signals.
Why am I talking about video signals if you're here to find out about surround sound systems?
Well, modern AV receivers have started to blur the edges between audio and video signals.
They are designed to simplify the connections in a complicated home cinema system and therefore you can use them to process audio and video signals.
Anyway, more about audio and video signals in a moment - first, let's talk about names...
It is called an AV receiver rather than an amplifier because it has a built-in radio tuner.
Even if you don't want a radio tuner, these days most home cinema surround sound receivers will have a built-in tuner - and therefore it will be called a receiver rather than an amplifier.
Although less common, you can get surround sound amplifiers without a built-in tuner - they will probably be called AV amplifiers, home cinema/home theater amplifiers or multi-channel amplifiers.
To make things easier, I will always refer to a multi-channel amplifier as an AV receiver, since this is the most common type you will find when you are looking to buy a device of this kind.
Now, let's have a look at the details of an surround sound receiver, starting with the sound...
Firstly, an AV receiver is a multi-channel amplifier.
It will have several different audio inputs to take all the audio from your input devices.
You may have devices that output audio by stereo analog phono connections, by digital optical connections or by HDMI connections. Whichever way the audio is sent, you should have enough inputs on the back of your AV receiver to connect them all.
The AV receiver will process the 5.1 surround sound mix when you play a DVD - and then send the sound to your 5.1 or 7.1 speaker system.
There are many things to look out for when checking out AV receivers - but one of the main things is their surround sound capabilities.
When you are looking at possible AV amplifiers to buy - it should specify if it is a 5.1 or 7.1 amp. This refers to how many speaker connections there are on the back of the unit and if it will process 5.1 or 7.1 soundtracks.
Most DVD/Blu-ray movies will come with a 5.1 soundtrack - and all AV receivers will be able to connect to a 5.1 surround sound system.
If you get a receiver that is capable of 7.1 surround sound (it will have two more speaker connections on the back) - you can still use it for just 5.1 sound if you want.
7.1 soundtracks aren't very common, however the 7.1 surround sound receiver will be able to process the 5.1 mix and send audio to the extra speakers at the back via digital processing. Therefore it can add to the sense of space in the room.
You may also come across a receiver that says it supports 7.2 surround sound.
The '.2' means the receiver has an extra subwoofer output for connecting two subwoofers.
You may think a 7.2 soundtrack would have two separate LFE tracks to create a left and right bass effect (in addition to the normal surround sound channels) - however this doesn't actually happen on any current soundtracks.
So what's the point of a 7.2 channel AV receiver?
Well, the extra subwoofer can be useful to reinforce the bass sound in your room - especially in larger rooms. It is quite common for the long bass waveforms to cancel each other out in various parts of the room, which means the bass level can vary depending on where you are sitting.
You can compensate for this by adding another subwoofer in another part of the room and this can help to even out the bass sound.
You could also create this dual subwoofer effect by splitting a single subwoofer output with a 'Y' connector.
The soundtrack for a movie on a Blu-ray disc or DVD that you play will come in a number of different formats - usually a combination of high-resolution and lower resolution sound.
The two main audio formats are by Dolby and DTS.
To play a particular soundtrack, your AV receiver will need to be able to receive, decode and output them.
High-definition audio formats, Dolby TrueHD and DTS-HD Master Audio, may be supported by the an AV receiver - but also may not, so be careful here.
The AV receiver will have to be able to receive the HD audio data over an HDMI connection (no other digital connections support HD audio), and it must also be able to decode the data.
If the AV receiver cannot decode Dolby TrueHD or DTS-HD Master Audio, then you will need a Blu-ray player that can do the decoding before it sends the audio to the AV receiver.
The receiver should also provide other signal processing technologies such as Dolby Pro Logic II and DTS Neo:6 which can take a stereo signal and create a 5.1 surround sound mix - therefore making full use of your multi-channel speaker system even with a stereo sound source.
Most TV programmes are still transmitted in stereo and so you can enhance the audio of everything you watch by using your AV receiver to process the stereo sound.
Movies and sports benefit from this in particular as you will feel like you are more in the middle of the action. It's not as good as a proper 5.1 surround sound mix that you get on DVD or Blu-ray, but it can be quite effective. As well as those mentioned already, there are many other audio formats that your AV receiver may support, go to the guide to surround sound formats for more details.
If you have a good memory, you'll remember I mentioned at the start of this article about video signals.
So what was all that about then? I thought we were talking about audio amplifiers and surround sound?
Well, it used to be the case that an AV receiver was just an amplifier for the sound.
However, these days you will find that an AV receiver will also accept the video signals from your input devices too.
What's the point in that? I thought we could send the video signal straight to the display?
Well, you could. But think about it.
If we can send ALL the signals - video and audio - from the DVD player, Blu-ray player, cable TV box, Wii games console, PS3 console etc into the AV receiver - then the AV receiver can handle all the switching of signals when we change inputs.
Also, we can then have just one video cable connected to the display for all sources.
For example, when I select the 'DVD' on the AV receiver - the receiver selects the correct inputs for the DVD (audio and video), and sends the DVD audio to the speakers and the DVD picture to the display.
When I select 'Cable' on the AV receiver - the receiver selects the correct inputs for the cable TV box (audio and video), and sends the cable TV audio to the speakers and the cable TV picture to the display.
I haven't got to worry about selecting different inputs on the amplifier and the display - and it is much neater as there are less cables required to connect it all together.
Isn't that much easier?
In the example above, we have connected the DVD player and the cable TV box to the receiver with an HDMI cable. This sends the picture and the sound down the same cable and is the best connection to use if your devices have this connection type.
If you don't have HDMI on all your devices, then the beauty of an AV receiver is that it will have many different connection types at the back to enable you to connect your devices. This is why the rear of AV receivers can look so complicated. In reality you won't use many of these extra connections, they are just all there to give you the flexibility for connecting a wide range of devices. You are not expected to use every one!
One important thing to think about when looking at AV receivers, is the ability of the device to upconvert or upscale a video signal.
By upconverting I mean, can it receive one type of video input (e.g. analog component) and output it as another (e.g. digital HDMI)?
If it can't, I will have to send the component video signal to the display via a component connection - which means more cables to the display if I am already sending something else via HDMI.
It may not be the end of the world if the AV receiver cannot upconvert various types of inputs - but just be aware that this may be a limitation if you are hoping to keep the cabling of your system as simple as possible.
For upscaling, the aim is to convert low resolution material into a higher resolution i.e. from 576i PAL to 1080p.
If the receiver doesn't upscale, then this job could be done by the Blu-ray/DVD player or the screen itself - so again, it may not be something you need in your AV receiver.
So where do you start when looking for the best AV receivers?
There are a few manufacturers building very high quality surround sound receivers - and there are a range of options depending on your budget.
As with everything, a more expensive model will normally mean it has better quality components (it should look and sound better than a cheaper model), and it will have more features (but do you need those extra features?).
However, these are only general assumptions, so you need to look into exactly what each model will offer.
The main manufacturers of AV receivers are listed below:
These are some of the best brands to start looking at when you are in the market to buy.
The main things to look out for when looking for an AV receiver are:
So as you can see, you really do need an AV receiver or amplifier if you want a surround sound system.
Not only does it decode the digital soundtrack from your DVD or Blu-ray disc, and powers your multichannel speaker system - it also gives you control over the video inputs too, making switching and cabling much easier.
You can get a good sound by using a stereo amplifier - and if you have an existing stereo hi-fi system you may be able to use this - but the problem is you will be limited to stereo sound.
The real fun begins when you have a surround sound installation. It really does add to the enjoyment of movies and television that you watch in your home, and you will be missing out on half the fun without it.