5.1 Vs. 7.2 (Surround Sound System)

Question

I fairly learned about the 5.1 studio and how you go about mixing it, but on Tv i heard about 7.2 surround sound system and i'm wondering are the dynamics the same or is there something different about it?

Answer 1

Just to clarify, 7.2 isn't about directionality of the sub. There isn't a left and right sub per se, because subharmonic frequencies aren't directional. It's very difficult for the ear to perceive exactly where 40Hz is coming from. It's more about spreading the sub evenly around a room.

Here's an article about various home theater speaker layouts.

Here's a previous thread about 7.1 vs 5.1.

Answer 2

The bit I learned about 7.1 as opposed to 5.1 has to do more with enveloping the listener within the sound field. I went to a THX course over six years ago where one of our instructors explained that 7.1 surround had already been adopted as the standard for the gaming industry, because it allowed the gamer to be more engulfed within the sound field (creating a more realistic gaming experience).

It allows for more accurate placement of sound toward the sides & rear of the sound field, thus allowing the sound mixer a larger canvas to paint with. It's become the standard for mixing films shot in 3D because of the same reason. The link posted above by Justin Pearson is a great source for explaining this.

The three dimensionality in sound gained by 7.1 over 5.1 has to do with adding two extra speakers sitting further behind the side speakers (I've seen them usually placed behind the listener projecting straight forward), creating more "Space" in the back of the sound field (more speakers means more places to put sound) for sounds to be localized or moved around in. Whereas with 5.1 the sound field is limited toward the rear because the Left Surround and Right Surround speakers are at the sides (sometime just behind the listener at their side) of the listener, with a very wide displacement of rear sound sources. Because of the wide displacement of the rear speakers and their placement at the sides of the listener, any sound panned between these speakers can seem to disappear from the back of the sound field as it moves through the listeners head and reappear as it moves toward the other speaker. The two extra speakers in a 7.1 setup allows extra "space" for the sound to pan through the sound field behind the listener, thus creating a more realistic movie experience.

The good thing is that 5.1 mixes can be adapted to 7.1. 5.1 is still the standard, for the most part, when it comes to mixing sound for picture. It can be adapted to any playback format and is still widely in use for DVD and broadcast. I have to admit, I've spent more time mixing on set and over the shoulder without the need to think about playback standards, other than HD sample rate and +0.1% pull up, so if there are new standards to know I'd love to be schooled by any of you who live in that realm full time. I love sound!

E. Santiago

Answer 3

I'm not entirely sure what you're asking, but 5.1 and 7.2 are VERY different. In 5.1, you have right and left front, right and left rear, center and sub. 7.1, you have all that, except sub is split into right and left, and you have additional right and left side speakers.

So, when you're mixing, some things that would fully occupy left front and rear speakers in 5.1 could almost completely be housed in left side. Sub is no longer mono, which means you actually have to think about which direction the low tones are coming from. Also, twice the low-frequency channels means you may end up with too much bass. Same for anything that happens in the side channels. If you simply add those to a 5.1 mix, things that happen on the sides will have more weight because they're happening in 2 or 3 speakers, instead of just the one set.

All in all, just as 5.1 is totally separate from stereo, 7.2 is separate from 5.1.

Answer 4

It's really dependent on whether you have it set for music or movie.

In the case of 5.1 music - 7.1/7.2 they combine the signals from the front & rear to create a side channel.

6.1 (which you don't see as much) takes a little more not only do they combine the front & rear signals to they also combined the rear L&R signals to create a rear center channel.

With that out of your head now to the movies to upscale from 5.1 - 7.1/7.2 is similar to the way they upscale 5.1 music to 6.1 but instead of just having the rear signals combine & split it into 2 separate channels the way they combine the signals and split them into 5 or 6 or even 10 individual channels (notice I haven't said anything about the front center cause it doesn't change from 5.1 - 7.1/7.2/6.1) is the key to a seamless transition from the front to the rear of your room.

Answer 5

A side point, I know having more speakers like 7.1 instead of 5.1 will make a big difference, but people tend to forget about compression!

I'm not so sure about home appliances but when it comes to Cinema sound, the average 5.1 system in cinemas is AC-3, Dolby Digital. IMAX is also only 6 channels but UNCOMPRESSED audio. That makes a heck of a difference!

Another very typical scenario in Cinemas is 7.1, like with Sony SDDS. The compression ratio is around 5:1.

Less compression really does make a huge difference, and of course it has a direct result on dynamics.