How does surround work?

[Antimon]

I would like to know more about the basics concerning how using more than two speakers affect what you hear. Any good links or articles?

For instance, if you hear a sound for the first time, and you can't see anything connected to the sound (maybe it's dark), how do you know if it's directly in front of you or directly behind you? Is it possible to confuse front with behind? Does surround have any point if the listener doesn't move around?

I used to be sceptical when friends started buying 5.1 receivers for their DVD players and big screens. I was thinking: we only have two ears, right? Wouldn't having more than two speakers be as pointless as "trioscopic vision" (a 3d system with three eyepieces). I think I've realized that more speakers give a different sense of space, but how does it work?

Also, how do you simulate, say, a quadraphonic environment in stereo headphones?

/Stefan

[jksuperstar]

I don't have my links accessible right now, but I can give you a run down of *my* understanding. I'll make some analogies to sound underwater, simply because water is a very efficient carrier of waves, and it gives a clear comparison of two drastically different environments where locating sound in a 3-D field is noticably different.

Your head resonates (bones), and your inner ears pick up on this. This particularly is true for low-frequency content. Sounds coming from the left, vibrate through the head to the right ear, etc. Ever been in an anechoic chamber? It's very strange, sounds coming from one side, seem "overly panned" if I could describe it in words. Like the sound is extremely intense in one ear, and very dull in the other. Underwater, many sounds feel like they're inside your head because water transmits these sounds to your skull so efficiently.

Also, the shape of the ears help define the directionality of what they hear, because they effect the frequency spectrum in a directional manner -- ie: we hear certain frequencies from the front in a more clear fashion, while the same sound from behind will have these frequencies attenuated. This may not be noticable, but the brain is always analyzing this information. When creating a sound to be heard for the first time (synthesis), if that sound was created to have a frequency content reflecting the balance found in naturally existing sounds, attenuation of frequencies can then help in "placement" of these sounds in a surround field. In essence, our brains are trained to hear "naturally" occurring sounds, and can place those sounds in an environment based on the frequency and phase information received. Go under water, and you'll notice it's difficult to place sounds, because your outer ears are bypassed by the efficiency that water carries vibrations. Especially for higher-frequency sounds.

Our two ears also perceive phase information, ie- the time it takes for the sound to reach one ear first, then the other. Lots of filtering, shitty amplifiers, poor mixing and mastering, room acoustics bouncing all over the place, etc. all change this information. A good system that preserves this info makes a HUGE difference in the perceived sound field. Going to 5.1 helps around these problems, but doesn't solve them. Then there are sound systems that USE this changed acoustic environment to an advantage, this is the premise of many Bose systems, such as that expensive clock-radio they make. In that case, they aren't trying to re-create a stereo image, but instead destroy the image altogether and confuse the brain enough not to be able to locate the sound, hence the feeling of "being surrounded" by the music. Under water, you'd notice the sounds that might be locatable are those that have a strong wavefront: a tap, a click, or other sound that can clearly be differentiated when it hits one ear, then the other. However, sound under water travels at different speeds, so we feel like we hear a direction, but still get confused about exactly where it's coming from.

[mosc]

There is some good information on Robin Miller's web page, http://www.filmaker.com/surround.htm . Robin is a member here. He gave a great talk at electro-music 2005. He is working on systems for 3D sound reproduction with speakers above and below the listener, as well as surrounding on the horizontal plane.

The psychoacoustics of hearing spacialization is an area where there is still significant ambiguity. I have learned a lot about it by having lunch with Robin almost once every week.

I for one am not interested in reproducing sounds or accurately placing them is space, but in creating beautiful electronic sounds and textures. For example, imagine you are surrounded by a thousand buzzing bees. Do you have to accurately emulate every bee or can you do an effect?

More on topic, it is true you have only two ears, but the shape of the pinna does make subtile colorations (changes in frequency response) of the sound that go a long way to assist the brain in localzation. Your brain knows the subtile changes in your pinnas. I suspect if you were given someone else's pinnas you might be disoriented for a while. This works for front back localization as well. When walking in the park, I'm often amazed how well I can localize a bicycle approaching from the rear, or birds in the trees overhead.

One thing I have noticed is that your brain gets a lot of clues when you move your head. If you force you head to remain perfectly still, your spacial perception becomes less effective.

[mosc]

Note: Kassen posted here. I started a new topic. See: http://electro-music.com/forum/topic-10529.html

[mosc]

[Antimon]

Thanks for the info! I think I'm going to pick out my little four-speaker computer speakers and experiment in a noodle...

/Stefan

[mosc]

Yes, the G2 is a good device for experimenting with quadraphonic sound. Please let us know what you come up with.

[diatonis]

Hi,

There is a great PDF file for anyone interested in surround sound:
http://www.grammy.com/Recording_Academy/Producers_And_Engineers/Guidelines/

Download the 'Recommendations for Surround Sound Production' PDF file and take a look. Most people seem to have questions about how bass management works and what type of speakers to use. (The LFE channel is not the same thing as the SUB channel - use the same speaker type and model for all speakers). There's a lot of info in this pdf.

As far as equipement you might need depends upon 'how much (money) you have ' and what you want to do. There is no limit!

There are many way to deliver 5.1 audio:
Windows Media Player/Encoder allows both lossy and lossless 5.1 playback (lossy with video): http://www.microsoft.com/windows/windowsmedia/forpros/encoder/default.mspx

You can use a somewhat new player as well as encoder from Fraunhofer:
http://www.all4mp3.com/
The Player contains ensonido which is a head related transfer function type of player that allows you to playback 5 channel audio from a stereo system (headphones or speakers). AAC also supports surround.