dbx 1231 - Digital Zone Processor

dbx 1231 - 31-band (1/3-octave) dual graphic equalizer with Constant Q, ±6/±15 dB and Low Cut at 40 Hz

The dbx 1231 is a 31-band per-channel stereo graphic equalizer designed for professional sound reinforcement and demanding installations. A dbx 12 Series member, the 1231 combines 1/3-octave bands with Constant Q response for predictable tuning, a switchable ±6 dB or ±15 dB boost/cut range , a 40 Hz 18 dB/oct Bessel low cut filter , and ±12 dB input gain . It employs 1.8" (45 mm) center-detent faders with front-mounted switched bypass and 4-segment LED meters per output for level monitoring. With XLR, 1/4" TRS , and barrier strip connectivity, electronically balanced inputs and servo-balanced outputs, the 1231 delivers extremely low noise, THD+N < 0.005% , and range from 10 Hz to 50 kHz .

Its construction includes a magnetically shielded transformer , an RF filter on the I/O, a power loss bypass relay (2-s power-on delay), and a chassis/signal ground lift option . All this is housed in a rugged 3U metal chassis designed for years of intensive use in PA systems, monitors, studios, or fixed installations.

Main features

• Dual 31 bands per channel, 1/3 octave , with Constant Q for consistent cuts/boosts at any level.
• Boost/Cut switchable : ±6 dB (fine adjustment) or ±15 dB (coarse correction), LED indication.
• Low Cut Bessel at 40 Hz (18 dB/oct) per channel to control headings and infra-bass.
• Input gain ±12 dB (41-position rotary control) to match system levels.
• Front panel EQ bypass and LED output metering (−10/0/+10/+18 dBu).
• Complete connectivity : XLR , TRS 1/4" and barrier strip on inputs and outputs; chassis/signal ground lift .
• Professional I/O : electronically balanced inputs and servo-balanced outputs , RF filtered.
• Operational safety : relay hardwire bypass on power failure/disconnection (2 s delay on power-up).
• Performance : <10 Hz–>50 kHz (+0.5/−3 dB), DR up to 115 dB (±6 dB range), THD+N <0.005% , crosstalk < −80 dB.
• Format : 3U rack, dimensions approx. 134 × 483 × 201 mm , weight approx. 4.8 kg .

Product benefits

• Precise and repeatable adjustments : Constant Q response maintains selectivity of each band.
• Correction versatility : switch between ±6 dB and ±15 dB depending on whether you need fine retouching or more aggressive surgery.
• Noise-free integration : Balanced I/O, RF filter and ground lift minimize hum and ground loops.
• Tour reliability : relay bypass in case of network failure and reinforced 3U chassis for intensive use.

Use cases

• Main PA and monitors : room/stage equalization, resonance control and headroom before feedback.
• Commercial installation : tonal adjustment of zones in theaters, temples, auditoriums and entertainment venues.
• Studio/Broadcast : Quick fixes on outboard sends, sums, or chains.

Frequently Asked Questions

• Is it digital or analog? The 1231 is a 2-channel analog equalizer with fixed 1/3 octave bands.
• What's the difference between the 231s and the 131s? The 1231 is part of the 12 Series (3U, XLR/TRS/barrier strip connectivity, ±6/±15 dB, 40 Hz/18 dB/oct Low Cut, and bypass relay); the 2-Series (231s and 131s) share the same philosophy but have different chassis and specifications.
• Can I insert it between the mixer and the power amp or into an insert? Yes; its maximum output level of > +21 dBu and balanced I/O allow for both topologies.

Description for projects

dbx 1231 Graphic Equalizer ; 2 channels, 31 bands /channel (1/3 octave, Constant Q ); ±6/±15 dB boost/cut (switchable); ±12 dB input gain ; 40 Hz Bessel high-pass filter 18 dB/oct ; EQ bypass ; LED output metering −10/0/+10/+18 dBu ; Female XLR , 1/4" TRS and barrier strip inputs (electronically balanced, > 40 kΩ bal. / 20 kΩ unbal., max. > +21 dBu; CMRR > 40 dB typ. > 55 dB at 1 kHz); male XLR , 1/4" TRS and barrier strip outputs (servo-balanced; 200 Ω bal. / 100 Ω unbal.; max. > +21 dBu at ≥ 2 kΩ; > +18 dBm at 600 Ω); performance: <10 Hz–>50 kHz +0.5/−3 dB , usable band 20 Hz–20 kHz +0.5/−1 dB , DR 115 dB (±6 dB) / 109 dB (±15 dB), THD+N < 0.005 % , crosstalk < −80 dB; functions: chassis/signal ground lift , RF-filtered inputs/outputs , relay hardwire bypass on power off (2 s power-up delay); power supply 100/120/230 V~ , consumption 24 W ; 3U format ; dimensions approx. 134 × 483 × 201 mm ; weight approx. 4.8 kg .