A surround sound home audio receiver is the core element in the audio portion of your home theater. It takes the signal from the input, such as a DVD player, a smartphone, or anything else that creates an audio track, and transforms it to make it more intense, then pushes the amplified signal to your speakers. It truly makes your whole system work, as if it were the quarterback of your home theater.
There are many different audio receivers on the market, and the best way to categorize them is not by price or by one overall characteristic, but by feature set. There are several important features a receiver can have, and two different households can have totally different preferences over them.
HDMI is a standard for plugs and outlets. It is the highest-quality connection for signal quality, and as a result essentially every home entertainment device that you bought in the past five years will use it. That means you might need a lot of HDMI ports. At the low end, a receiver might have 3 ports: for your TV, a DVD player or Blu-ray player, and a wild card slot for a game console or some other device. Households with more devices might need closer to six HDMI ports. Think about what you use now and how many devices you have. There is no need to get more HDMI ports than you need. A good rule of thumb is to aim for one more port than you use right now. That leaves you with room to expand. In a worst-case scenario you can buy an HDMI switch to expand your ports.
The newer generation of receivers have started adding Wi-Fi to their collection of features. While few people are using multiroom audio right now, the real draw is the ability to stream audio from different devices over your wireless network. For example, if you use a music streaming service on your smartphone, you can stream it right to the receiver, which will push the signal to your speakers. That will translate into a huge boost in audio quality and immersion over your earbuds or phone dock. In addition, it is always possible that even if you do not use any Wi-Fi features now, you will start using them once you have the opportunity.
Audio receivers do not all push signal equally. This is an important feature because a small or weak receiver cannot fill a big room with sound. In general, if you have a bigger room, you need a more expensive receiver to have a strong amplifier that will be able to fill the room. Otherwise, the sound will feel weak and possibly distorted. If you have a big TV, then you will also want a big receiver, because having a large image with a small sound will feel strange.
It's worth saying again: the biggest things that separate receivers is strength of signal and features. Audio quality depends more on your speakers. Try to decide which features are must-haves and which are not. Be careful of fads and trends: the manufacturers love to add new features that don't give you much more value.
Right now, most home setups have a 5.1 channel system, powering 5 positional speakers and a subwoofer. 7.1 gives you two more channels. You can send these to two additional speakers if you have a 7.1 speaker system or even send two channels to each of your front side speakers, giving them more depth.
Most receivers actually produce fairly similar sound quality regardless of price. Don't get hooked into paying too much for a nominally higher quality, because a cheaper one will probably sound just as good. On the orher hand, it has to meet a certain minimum quality, so make sure you listen to them first- preferably, not in a store.
If your receiver's wattage is too low, the amp will overheat trying to push the signal to your speakers. The bigger and stronger your speakers are, the more important it is that you get a receiver with a lot of power. This isn't just about quality: you can damage the amp and speakers with an under-powered receiver.
You need to be careful about both overpaying and underpaying for a receiver. On the one hand, they are not that different from one another. On the other hand, the features that do differ matter. Power, durability, HDMI ports- these are all make-or-break aspects, and they all affect price.
Brands of receivers tend not to differ that much- it matters more where on the price spectrum you are. However, there is one brand, Marantz, that is known for top-shelf music playback quality. Other brands, like Yamaha and Sony, are better at all-around performance. The first thing to do is decide on a price range that you are comfortable with and a list of features that your receiver must have. Then take into account the size of your TV, speakers, and room. That all adds up to determine the shortlist of receivers that works for you. Don't worry too much about audio format- most modern receivers can handle the most important surround sound formats. When possible, it is a good idea to save money on the receiver and put that into speakers instead.