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SP 451 Surround sound processor

Soundfield SP451

The SP451 Surround Processor expands the possibilities within the SoundField range of analogue microphone systems to offer a complete 5.1 surround, stereo and mono microphone package. The SP451 is designed to accept the four channels of B-Format information generated by SoundField Microphone Systems. This can occur live as the performance takes place, or retrospectively from pre-recorded B-Format in a post-production environment. The SP451 reconfigures the B-Format into a five cardioid pattern mic array to deliver a high quality, full band, discrete Left / Center / Right (L/C/R), Surround Left / Surround Right (SL/SR) mic output plus a further sub-bass (LFE, <120Hz) output.

Soundfield SP451

• B-Format input metering with level control

• Front Width adjusts the angle of Front Left/Right mics by ±45 degrees

• Rear Width adjusts the angle of Rear Left/Right mics by ±45 degrees

• Rear Focus enables adjustment of the rear pair microphone polar patterns

This control adjusts the input level of all four B-Format channels simultaneously and is variable from full attenuation to a gain of +10dB. Normally this control should be used at or close to its 0dB position. Four 12-segment bargraph level meters are provided to monitor the levels of the W, X, Y and Z signals following the input gain control.

Front Width:
When the Front Width control is set to its CAL position, the angular positions of the Front Left and Right virtual microphones are at -45 and +45 degrees (relative to Centre) respectively. This control narrows or widens these angles symmetrically. The resulting range is from 0 degrees (Mono) to a very wide and exaggerated perspective of ±90 degrees relative to the Centre.

When the Rear Width control is set to its CAL position, the angular positions of the Rear Left and Right virtual microphones are at -135 and +135 degrees respectively. As above, this control narrows or widens these angles symmetrically, with a range from 180 degrees (a monophonic Rear Centre) to ±90 degrees relative to the Rear Centre position.

Rear Focus:
When set to its CAL position, the polar patterns of the virtual Rear microphone pair are as established by the MAP card. If the MAP card defines the rear mic positions as cardioids (default with the included card), the Focus control may be used to vary the patterns of these virtual mics from omni, through cardioid, to figure of eight. This degree of control can be very useful for adding additional spatial information to the rear surround channels, especially in ambient or freefield environments.

From the SP451 Input Section the B-Format outputs, either in real time or from tape, the SP451 delivers a high quality, full band, discrete Left/Centre/Right (L/C/R), Surround Left/Surround Right (SL/SR) 'mic' output plus a subwoofer (<80Hz) 'mic' output. Each of these six 'mic' outputs has its own level control and output level meter, plus the five mic array has individually definable mic patterns. The mic patterns are determined by an internally installed SoundField MAP (mic array pattern) card. One MAP card is included as standard with the SP451 which is a cardioid L/C/R/SL/SR card. An optional second and third card can be added to the SP451 set up in almost any 5 mic array configuration imaginable. Any of the three cards can be selected from the front panel to apply a different mic array pattern to real-time B-Format or B-Format recordings.

Each of the 5 microphone locations is based around commonly accepted surround mic positions of Left (at -45 degrees), Centre (0 degrees), Right (+45 degrees), Surround, Surround Left (-135 degrees), Right (+135 degrees) with a Sub out (summed from all outputs below 80Hz). Add to this impressive list of operational modes the option to change the front Left/Right microphones and the rear Left/Right microphone positions by +/-45 degrees from their 'centre' position, and the SP451's flexibility becomes apparent.

SP451 Surround Outputs

• Three MAP card selector switches with LED status are provided. The SP451 is shipped with a standard 5.1 card fitted in the MAP1 position. Two other MAP card selector switches are available to accommodate future surround formats.
• Full band, discrete Left/Centre/Right/Rear Left/Rear Right and Sub-Bass outputs are provided, each with individual bargraph metering and level control
• Two additional rear panel outputs numbered 7 and 8 are provided. These continually output Left/Right stereo - the stereo width is defined by the Front Width control

The six Output controls adjust the respective levels of the outputs 1 to 6. An eight-segment LED level meter shows the post-gain control signal level. The alpha-numeric displays above the meters are determined by the MAP card being used, and show which surround channel is being controlled. The gain range of the controls is from full attenuation to +10dB of gain. The levels of outputs 7 and 8 are fixed at 0dBu (equivalent to setting the output potentiometers to ‘0’ on the variable levels of outputs 1 to 6).

Surround Mode – MAP (Microphone Array Pattern) Selector:
The SP451 can accommodate up to three MAP cards - positions 2 and 3 are to accommodate future surround formats.


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