How exactly is surround sound "made"?

[Jabez Scratch]

I'm no sound engineer so I've often wondered how surround sound is created.

Is it all post-production in a studio? Does a sound engineer take the soundtrack and allocate certain sounds to one channel and other sounds to another channel?

Or is it done on set, i.e., with, say, five microphones picking up the sound that they are pointed at to create the five channels? Or is it a combination both? I have no idea, but I'm curious to know.

[HornEd]

You are not alone, Jabez, and maybe that even extends to manufacturers! In modern times, the "real" music is made from assorted tracks recorded live and special electronic treatment of those tracts as many tracks are resolved into two (stereo) six (5.1) or seven (6.1). Most sound systems are not configured to get the most out of what is available on a modern DVD or CD source.

When "surround sound" was first envisioned decades ago, the notion was to have a third channel that had "audio clues" on it to fool your ears into thinking a better set of speakers were all around you. Your ears will pick up sounds from an original source and then use secondary reflections to determine where that source is. It will also apply that "direction" to other sounds that it associates with the first sound.

For example if you had a subwoofer in front of you producing the low level (non-directional) sounds of a car crash and a small rear speaker giving out sounds associated with the car crash at over 85 Hz, your ears would tell you that the car crash happened behind you... even though most of the sound would be coming from in front of you.

In the bygone era of ProLogic and early THX, surround sound was intended to create ambiance... and special speakers were used to diffuse the sound and fool your ear into thinking it was always completely immersed in sound.

Enter the modern era. With five or six main channels to work with... plus a low bass channel... the sound engineer can create just the right ambience by directing sound mixes into one or more channels. If, for example, the sound engineer fed some background sound into all five (or six) channels, then the effect would be like di-pole speakers put into your listening area... only di-poles are really out-of-phase gimmicks that attempt to make up the shortfall in surround sound potential in acoustically challenged rooms.

Modern surround sound systems should be able to bring the best of both worlds... ambience and event directionality. I am in a hurry today... I hope that helps to get the discussion started. -HornEd

[WMcD]

I've read, somewhere, that in classical music, surround is picked up by microphones back in the hall. Let me add that rock concerts must use this for audience noise too.

Now that is doubtlessly true for NFL football too. Over Thanksgiving we watched football at the rental condo in Florida. The set's audio was set to the SAP channel, which carried surround. The commentators were talking and all we could hear was crowd noise. Going to the main feed solved that.

Movies, of course, are a different story. Many of the effects are created separately.

E.g. the sound of flying bullets are not actually generated on the set; flying bullets being fairly dangerous. I doubt the sound of chirping birds, traffic, rainfall, thunder, are "live" on most sets. It all gets mixed later.

This isn't any more cheating than most of what goes on in movie audio. You may have viewed outdoor scenes where the actor's voices are particularly clear . . . much moreso than could be achived with overhead mikes. This is because the actors have to dub it in in a studio.

Gil

[cluless]

They throw the 2 channel recording in a blender.

Wheeeeeeeeeeeeeeeeeeee!