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Documentary ambient sound: stereo and surround recording

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DavidP
Documentary ambient sound: stereo and surround recording
on Nov 6, 2006 at 7:33:50 am


I am fairly new to film sound (but with a bit of audio experience) and I was recently brought in to a documentary project to develop and mix the audio (create/find sfx, ambience, etc). I was not on the project when the film was shot, and the audio is exclusively camera sound (and lav mics for interviews). So now I am preparing to recreate at least the ambient aural experience in post - but I'll stick to as much of the sync sound I can reliably use. I am required to construct a 5.1 mix as well as a stereo mix. My current location sound gear is a Marantz PMD671 CF recorder and a pair of Rode NT5's mounted as a coincident pair or ORTF as the scenerio dictates.

My question is this: is it possible to create a reliable 5.1 mix using only stereo ambient recordings? I suppose this depends on the types of ambiences - the majority of this film is outdoors on the water - lots of water gurgles and splashes.

Or is it in my best interest to purchase a four channel CF recording device (I'd extract the center channel from L and R), two more mics, and create a surround array for remote recording? Obviously, I may not have the resources to purchase this equipment, but if the film can't live without it, I'll find a way.

Thanks for your help,

David



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Will Salley
Re: Documentary ambient sound: stereo and surround recording
on Nov 8, 2006 at 3:35:45 am

I'm not as experienced mixing 5.1 as many, but I have done enough to weigh in and try to give an opinion. I've used a single stereo source to build a 5.1 mix with excellent success. As you mentioned, the center chaneel can be derived from L+R source, but I would leave the L+R sources intact and use only the mono interview source for center channel, care should be taken not to simply combine and boost the L+R sources for center channel. This is where I prefer M/S recordings. These can be decoded for your LF+RF source, and the M channel can be split for center and Sub sources. The next step is to take the original decoded M/S tracks and process them for the proper space and ambience (a 100% wet mix of reverb or delay, etc.) for the LR+RR sources. Mix the matrix to your liking and you've got it.

You can also buy a slew of plug-ins for Pro Tools to do some of this for you.


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DavidP
Re: Documentary ambient sound: stereo and surround recording
on Nov 10, 2006 at 4:06:08 am

Thanks for your help. I believe the approach of adding LS and RS ambience via spatial effects (reverb, delay, etc) is a fantastic method for mixing 5.1 music; however, I am faced with mixing outdoor ambient sound in 5.1. I am hoping to record a number of stereo takes of (for example) water gurgles next to a dock, and place them in the surround spatial environment - but I am not certain this can be done realistically. Is anyone familiar with this type of workflow?

thanks,

David



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Will Salley
Re: Documentary ambient sound: stereo and surround recording
on Nov 11, 2006 at 7:19:55 am

David, I don't know what your equipment budget is, but this is probably the best solution to what you're looking for - http://www.soundfield.com/
Combined with a hard-disk recorder such as the Sound Devices 744T, you could record in the Soundfield "B-format" and decode to 5.1 in post. It's very pricey, however. Mic-$5000+, Recorder-$4000

A less expensive option would be to purchase a Fostex MD-8 ($400 - records four tracks simulitaneously in 16 bit/44.1Khz) and four matched small-condenser mics. Arrange the mic tree in two x/y arrays, one facing forward and one facing reverse. Phase reverse both of the rear facing mics. Experiment with the angle of the rear x/y pair - you can enhance the surround effect by increasing the angle of coincidence to about 110 degrees. Since the Fostex is AC powered, you would be limited to locations.

There may be other 4-track portables out there that I'm not aware of.


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John Fishback
Re: Documentary ambient sound: stereo and surround recording
on Nov 19, 2006 at 3:46:02 pm

Another thought might be to combine the LS RS channels derived from delay, etc. with some point sources such as appropriate animals (or other) sounds from the rear.

John

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