On 12/31/14 17:10 PM, Dan Dugan [naturerecordists] wrote:
> There are three different standard sequences for surround channels on
> the recorder and studio console, Dolby, DTS, and I think SMPTE. I'm
> not sure whether encoding of the output goes by the channel names or
> sequence. When I made a surround DVD I let the authoring software
> (Apple Final Cut Pro and Compressor) encode the audio channels so I
> don't know what happened there. I wouldn't be surprised if authoring
> software has a preference to set for your preferred working sequence.
> Obviously the output medium has a standard channel sequence. I'd use
> the Dolby sequence.
There is a standardized sequence for channel mapping in
cinema/home-theater sound systems, which is simultaneously codified by
ANSI, CEA/CEDIA, and the ISO. Though all of those standards documents
are behind paywalls, this Wikipedia page is correct:
[ http://en.wikipedia.org/wiki/Surround_sound#Channel_identification ]
0:L, 1:R, 2:C, 3:LFE, 4:Ls, 5:Rs, 6:Lrs, 7:Rrs
Further, there is a ISO/SMPTE standard in development (also,
unfortunately, behind a paywall) that would specify these "immersive
surround" speaker locations:
24 on the horizontal plane at 15=C2=B0 intervals
5 on an arc inclined 45=C2=B0 above the left horizontal, at 30=C2=B0 interv=
als
5 on an overhead vertical (90=C2=B0 arc), at 30=C2=B0 intervals
5 on an arc inclined 45=C2=B0 above the right horizontal, at 30=C2=B0 inter=
vals
4 subwoofer locations: Front, Right, Left, and Back
These positions were determined by psycho-acoustic tests that attempted
to quantify the limits of spatial hearing acuity for 95% of the
population. They represent the maximum number of channels that would be
psycho-acoustically effective to deploy in a cinema setting.
> I've been recording soundscapes in surround for many years, using the
> standard Dolby channel names L, R, Ls, Rs. I use a technique described
> by former list subscriber Rich Peet:
>
> Your favorite stereo array for L and R
> Omni mics spaced 40' to the left and 40' to the right for Ls and Rs.
>
> Thus the front pair is imaging and the rear pair are uncorrelated (very m=
uch so, 80' apart).
Most of the "major name" cinema sound designers, at least those who I've
had the opportunity to hear talk on the subject, prefer to arrange their
mics for ambient bed recordings into arrays where the L&R are coincident
or near-coincident, and the Ls&Rs are 1.5m to 5m behind L&R, spaced
about the same distance apart as they are distant from L&R. Note that in
almost all cinema productions, the C channel is reserved exclusively for
dialog, narration, and key foley effects synchronized with on-screen
action, so C is not recorded as part of the ambient bed.
Those who differ from this, usually documentary producers or producers
in the faux-documentary style, prefer to use single-point solutions like
ambisonic (tetrahedral array) mics, or some of the other coincident
arrays (such as the Sanken 5.1 shotgun).
> I use a Jecklin Disk for my front array thus four identical omni mics in =
the system.
>
> The original Rich Peet technique is great for being on a trail. It
> only reveals its "defective" geometry when a jogger comes through! In an
> open space I usually pull the rears back 20' or so. Or position them
> opportunistically, like that bunch of trees there and those bushes.
I like the convenience of the Rich Peet technique for the reason that
Dan uses it. And as long as people and wildlife remain distant, it's
convincing enough.
> Steve Sergeant, a nature recordist who works at Dolby, has been
> encouraging us to add height channels to our recordings. I've done it
> once but I don't have proper playback set up yet to evaluate it. The
> minimum would be a stereo pair raised say 14', axis left and right,
> pointing up. A bit of a hardware challenge.
For height channels, I use an Audio Technica BP4025 on a 14' stand, with
the mic pointed straight up, and the capsules left to the left, right to
the right. Since the BP4025 actually has almost side-firing capsules
(wider than classic X-Y coincident placement), it's particularly good
for this task.
Most people don't expect the subtle addition of the height channels to
add as profound of an immersive effect as it does. At first, when you
turn them on, they seem to add little to the experience. But when you
turn them off again, it's like you suddenly became enclosed with an
oppressive roof overhead--it's at least a little disturbing.
--SteveSgt
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