SoundField for Surround
The four B-Format outputs from a SoundField microphone system may either be fed
directly to the SP451 during live productions or recorded to a multi-track recorder
and then played back into the SP451 for post production processing. These signals
are then used to create a 5.1 surround microphone array and the six surround channels
are routed to the mixing console for program production.
The five microphones of this virtual array represent the conventional Front
mic positions at Left (-45 degrees), Centre (0 degrees), and Right (+45 degrees);
the surround positions are at Rear Left (-135 degrees) and Rear Right (+135 degrees).
The LFE (sub-bass) output is derived from its own virtual omni microphone.
By processing the B-Format signals via the SP451, the mixing engineer has the
ability to create the optimum surround mic array configuration. Equally important,
the same B-Format signals can be processed in a variety of ways to meet the broad
range of needs imposed by differing audio delivery formats. Thus, a stereo music
recording for CD production, a mono feed for AM radio, and a surround soundtrack
for video or DVD all can be created either independently or simultaneously. All
this can be done either in "real time" or during any stages of post-production,
affording the mixing engineer the ability to create the ideal sonic perspective
under the controlled conditions of the production studio, rather than forcing a
decision during the original recording session that later may prove to be less
than ideal.
In order to avoid the confusion and complexity that could result from an infinitely
variable system (we are all familiar with the "too many knobs" syndrome) the SP451
processor uses plug-in MAP (Microphone Array Pattern) cards to define the basic
default polar patterns and angles of the virtual microphone array, and provides
the user with just the front panel controls needed to optimise this initial array
for any specific application quickly and easily. For example, the Front and Rear
microphone pairs in a 5.1 array may be adjusted ± 45 degrees from their default
angles, to suit any desired music and/or video reproduction system for surround
sound. Also, the polar patterns of the rear microphone pair can be adjusted with
the Rear Focus control, through standard cardioids for localisation of sound sources
to figure of eight for more spacious effects. When using 5.1 MAP cards outputs 7 and
8 provide Left/Right stereo, the width of which is decided by the Front Width control.
This facility was requested by broadcasters using the SP451 'stand alone' in a post
production situation with the necessity to generate both 5.1 surround and stereo
mixes simultaneously.
All of the outputs are at line level and represent the discrete outputs from
the microphones of the virtual array. No further SoundField processing is required
once the signals leave the SP451. The Rear Focus control enables the polar patterns
of the Rear microphone pair to be varied from omnidirectional through cardioid
(the default) to figure of eight. This provides significant adjustment of the
imaging and "spaciousness" of the surround channels.
The SP451 has three MAP card slots, with one card provided as a standard -
this cardioid L/C/R, SL/SR surround card will satisfy the majority of listening
situations. To provide additional versatility up to two further MAP cards can be
fitted to accommodate virtually any current or future mic array standards. Three
buttons on the front panel allow the user to make instant comparisons between up
to three mic arrays.
Forward-looking Capability:
Because surround sound formats are still evolving, the SP451 has an additional
two outputs numbered 7 and 8 in order to accommodate expanded formats such as 6.1
and 7.1. Furthermore, since the B-Format signals inherently embody the complete
three-dimensional soundfield information at the microphone position, any conceivable
future surround format can be addressed without the need to change the original
SoundField microphone system.
