How do camcorders record 5.1 or 7.1 surround sound??

[yoda313]

I've seen the newer camcorders boast about being able to record 5.1 surround sound. Now the newest high def format claims 8 channel surround (7.1).

How is this accomplished? I can't imagine it allows you to input 6 or 8 seperate mic's to capture true independent channels. How is it synthesized?

For that matter how do camcorders accomplish stereo recording when using only the built in mic?

[Marvingj]

5.1 means the recording has been made on five main channels - right, left, center, right surround and left surround - plus one for LFE (Low Frequency Effects), represented by the .1 in "5.1." When it comes to speakers, the terms 5.1, 6.1 and 7.1 represent the number of elements in the sound system. The difference between them is simple: it just depends on the number of surrounds - two for 5.1, three for 6.1 and four for 7.1.

The 7.1 channels of the receiver are really only, at most, 6.1.
(left+right+center+LSurround+RSurr+CenterSurr = 6).
The only differences between 6.1 and 7.1 systems is an extra channel of amp in the surround rear to provide 2 speakers in the rear instead of 1 (for 6.1)
The 2 surround-rear have the same signal, they are not stereo.

Some new DVD and theatrical releases offer DolbyDigital-EX or DTS-ES. DD-EX uses a matrixed rear-center, much like how you get a center channel from Pro-Logic.
DTS uses both a matrixed rear-center and also some versions have a REAL 6.1 soundtrack with a separate rear center, labeled as DTS-ES DISCREET.

As far as making a difference with having a rear-center speaker, It's entirely up to you. Some people don't hear a difference, but others, including me, appreciate the extra speaker. A lot of it depends on how well your speakers are set up and if your room can handle the extra speaker.

[jagabo]

For that matter how do camcorders accomplish stereo recording when using only the built in mic?

They have stereo mics -- essentiallly two directional microphones in one housing. It's not perfect but better than mono. There are many different designs. Google "single point stereo microphone".

some examples: http://www.minidisco.com/Microphones/Single-Point-Stereo-Microphones

I suppose this could be extended to 5.1 with four mics and some signal processing.

[Cornucopia]

The recording format may support multiple channels, but there aren't any consumer cameras made (and very few pro cameras) that allow more than 2 (or possibly 4 channels if using both mike & line inputs) channels at a time.

I also don't know of ANY format that "synthesizes" 5.1 from stereo. That's almost as bad as "synthesizing" stereo from mono. (and NO, I'm not talking about faking a DPLII output from a standard stereo input either, which sometimes works)

True recordings that have been done with multichannel sound are either done with multiple cameras, or with a camera and a separate audio recording setup. This is true of hollywood stuff too.

BUT--

You can do the next best thing:
Binaural! 8)
It's 2 channel, so that takes care of everybody.

Scott

[yoda313]

Thanks everyone.

@ Marvingj - I know how the professional dvds are made - I was curious about the personal camcorders that claim surround sound recording.

@ jagaboo - thanks I didn't know about that - interesting.

@ cornucopia - that is kind of what I was thinking.

[jagabo]

Cool in principle, Soundfield microphone:

http://www.soundfield.com/soundfield/soundfield.php

To 5.1:

http://www.soundfield.com/surround/surround.php