What is Surround Sound

Basics

If you’ve ever experienced a surround sound system when watching a film or playing a video game you know how amazing they can be. They are often labelled 5.1 or 7.1, depending on how many speakers and channels in the system.

5.1

5.1 is comprised of six channels, each with their own mono speaker. Three of them are in front of you: centre, left, and right. Two of them are behind you: rear left, and rear right. Finally, one channel is saved for the sub, which can be placed practically anywhere in the room except for the corners, which will result in muddy bass sounds. So, the 5 in “5.1” stands for the number of directional speakers, and the 1 stands for the sub bass driver.

7.1

7.1 is comprised of eight channels, with eight speakers. Just like 5.1, you have three speakers at the front and two at the rear. However, the remaining two speakers are positioned directly to the right at left of the listener. With a 7.1 set up, the formula is the same. Seven directional speakers, and one sub.

The Surround Formula

As explained above, the configuration of a surround system can be expressed as numbers. The examples given are simple set ups consisting of two ‘types’ of speaker; directional and sub. Directional speakers should be positioned carefully and turned to ‘aim’ them at the listener. The Sub speaker can go anywhere, as I explained before.

So far, we have a simple speaker formula:

Directional.Sub 

However, it gets a little more complex. We can add a third ‘type’ of speaker, speakers that are above the listener. 

Directional.Sub.Overhead

Now that we can put speakers in the ceiling, or use some clever speakers to bounce the sound off of the ceiling, we can start using systems like a 5.1.2 set up, or 7.1.2. This would mean we have a normal 5.1 or 7.1 set up, but with two additional speakers that play from above the listener to the right and left. This method is expandable and Dolby even have instructions on how to set up a 9.1.6 system. That’s 16 channels: 9 directional, 1 sub, and 6 overhead!

How does it work?

Surround Sound is a simple idea on the surface. You just have more speakers in the room and it makes the film, game, or music more immersive. It’s a more complicated beast for the person that has to make the film, game, or music.

The person who has to solve the issue of many speakers in film production is the Dubbing Mixer. It’s their job to take all of the dialogue, sound recordings, music, sound design, etc. and put it all together. Normally, they would only have two speakers to worry about; left and right. However, with a surround mix, they have to deal with six or more.

Here’s the general set up for a 5.1 mix:

Centre speaker:

  • Dialogue
  • Main Sound effects (gun shots, doors slamming, etc.)

Left and right:

  • Musical Soundtrack
  • Sound design
  • Sound effects
  • atmospheric sound (background noise)

Left rear and right rear:

  • Sound design
  • Special sound effects
  • Atmospheric sounds

Sub:

  • Low end sound effects (booms, thunder, explosions)
  • Sound design
  • Musical Soundtrack

Bear in mind, this is essentially a template and many sounds and effects move dynamically between speakers. For example, a common effect with a helicopter would be for it to initially play from the rear speakers when it is not on-screen, and when it flies over the camera and into view, the sound dynamically moves to the front.

When done well, a surround mix is exceptional. The immersion and complexity you can achieve is guaranteed to impress your listeners.

Dolby Atmos

Dolby, one of the largest Surround Sound developers, have created a system called ‘Atmos’. It supports up to 64 individual channels and 128 audio tracks! In a cinema, this enables the sound mixer to place elements in the soundtrack and effects precisely in the space of the theatre.

Normally, the mixer is only able to choose between 6, 8, or 10 channels to send their sounds. This is good, but it only allows for rough positioning like ‘to the right at the front’, or ‘behind and to the left’. Atmos, with its enormous number of channels and speakers has far more precise controls. You can choose to make a sound appear to be directly next to the listener, instead of from a speaker several metres away. You can move a sound in a figure of 8 pattern around the room. You could even record many individual people clapping, and simulate a realistic round of applause by playing 64 different recordings at once, spread evenly around the room.

The configuration for Atmos is complicated and has to be very precise, so it is not used everywhere. However, if you ever get the opportunity to try it out, you’ll be in for a real treat!

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