audio research

Surround sound processor.

From the ARC website

The SDP1 Multichannel Music Processor is intended to be used with any conventional stereo preamplifier to achieve a 5-channel matrix from two (stereo) channels of information. It does not use Dolby® noise reduction or steering logic. The SDP1 has rotary controls for adjustment of level (volume) of center, rear-right and rear-left channels; a fourth rotary control allows choice of time delay for the rear channels from a menu of 5 options ranging from 22 ms to 45 ms. Rear and center channels are operated at full frequency bandwidth, with a minimum of signal manipulation or processing; this helps insure tonal accuracy, transparency and best dynamics. Delay is achieved through advanced digital tech- nology, while gain circuitry (12 dB overall) is fully analog. Front L and R channels remain completely unprocessed at all times for maximum fidelity.

The SDP1 features both single-ended and balanced inputs and outputs (three outputs for connections to center and rear channel amplifiers). It is connected to a set of main outputs from the existing stereo preamplifier. Once the center and rear channel levels are set, the main preamp volume control becomes the master control.

While designed to meet strict sonic criteria for music reproduction, the SDP1 processor also performs amazing feats of resolution in video or theater applications. Coherence of the entire sonic envelope and ease of operation are the hallmarks of the SDP1.

Designed for use with the SDP1 processor is the SDA1 Four Channel Power Amplifier.





MSRP (US new retail)
$2,495. Later increased to $2,995.


Frequency response 2Hz to 400kHz (-3dB point), Center channel
Distortion (THD) Less than .01% at 2V RMS output. (Typically less than .002% at 1kHz)
Noise & hum Less than 30 uV RMS unbalanced IHF weighted, Center channel
Gain 12dB maximum (6dB balanced to unbalanced, 18dB unbalanced to balanced)
Input impedance 1.5 Mohms unbalanced, 3 Mohms balanced
Output impedance 30 ohms unbalanced, 60 ohms balanced
Maximum inputs  
Rated outputs Output before clipping: 18V RMS out balanced, 16V RMS into 600 ohm balanced load, Center channel
Power supplies  
Power requirements 100-135VAC 60Hz (200-270VAC 50/60Hz) 40 watts maximum
Other Output DC offset: Less than 2mVDC.
Inputs: Left, Right (balanced & unbalanced).
Outputs: Left, Right (pass through); Left Rear, Right Rear, Center Front (balanced & unbalanced).
Gain controls: Left Rear, Right Rear, Center.
Dimensions 19" (48 cm) W (standard rack panel) x 31/2" (8.9 cm) H x 113/4" (29.8 cm) D. Handles extend 11/2" (3.8 cm) forward of the front panel. Rear chassis fittings extend 9/16" (1.4 cm)
Weight 11.4 lbs. (5.2 kg) Net; 21.4 lbs. (9.7 kg) Shipping.


Vol. 18 No. 8