master the art of timing



Unlike other DSP room correction designs that include room acoustic effects in their measurements, DEQX processors (or preamp/processor) measure and correct a speaker's native anechoic response so that frequency-related phase, group-delay and frequency response errors are corrected before measuring again at the listening position and compensating for room acoustics.

The Platform

The HDP-Express is a stereo digital processor than can be installed between preamp and amplifier or as a preamp/processor. It's packed with innovative, patented speaker and room compensation technology. Almost half a million lines of code refined by our engineers over twelve years is what distinguishes DEQX from other digital processors and crossovers! Connected to a PC running DEQX software during setup, the HDP-Express first measures and corrects your speakers and subwoofers using its largely automated wizard-driven measurement, analysis, and correction software.

The HDP-Express uses Burr-Brown J-FET input op-amps and the same lightning fast Analog Devices (AD826) op-amps found in the HDP-3 for driving its stereo ADC and converting current to voltage following its six channel Analog Devices DACs.

The Express features SPDIF, AES/EBU, unbalanced and balanced analog inputs. Standard outputs on the three channels per side are unbalanced RCAs, and optional outputs include balanced analog or digital. Multiple HDP-3s can connect for multichannel surround configurations such as 4.2 and 5.1 to 7.7.

When using the HDP-Express as a stereo preamp as well as a processor – avoiding unnecessary conversions – you can be sure its audiophile quality all the way through. The balanced and unbalanced analog inputs are built around highly transparent Analog-to-Digital Converters (ADCs) running at 24-bit/96kHz resolution. Two SHARC 32-bit floating-point DSPs provide internal processing resolution on the order of 140dB followed by 24/96 Digital-to-Analog Converters (DACs) and six 256-step resistor-ladder analog volume control chips that maintain full dynamic range even at low listening levels. Nine separate power-supply regulation stages, including four that provide the main analog rails deliver extremely low measured distortion for fatigue-free listening.

While the DEQX Express can also be a set-it-and-forget-it experience, the remote provides volume control, input selection, four different speaker and room correction profile selections, plus low-, mid- and high-frequency tone controls. Even without a PC connected you can store 100 different EQ settings for different recordings or simple room EQ! You can use the bass, mid and high default settings, or for more precise control, move a band's center frequency across 10 octaves, with semitone resolution, while its bandwidth can be adjusted from just one semitone to four octaves with cut/boost in one dB increments.

The remote control also selects inputs: Two analog and two digital. One of the analog inputs might be connected to a phono preamp, an analog preamp or surround decoder, with one of the digital inputs connected to a CD or DVD player. Available with front panel 6mm black anodized.


If not working with a DEQX Agent in your home or studio and want to measure and correct the speakers and room yourself or via remote connection to a US Agent you'll need either the Standard Calibration Kit or Reference Calibration Kit. For the highest performance speaker correction DEQX recommends the Reference Calibration Kit with Earthworks microphone. The Standard Calibration Kit's Beringher microphone has a 20kHz top-end correction limit while the HDP-3 passes up to 40kHz. The HDP-4 also comes with DEQX Cal Software and Firmware.

The Method

Other "room correction devices" simply adjust amplitude response – uneven output at different frequencies – to offset room modes. But they don't address phase or group-delay timing issues that exist in all real-world speakers.


  • Provides DEQX Calibrated™ speaker correction for passive speakers
  • Audiophile grade analogue electronics
  • Frequency-response of speakers typically corrected from 6dB range to 1dB*
  • Automatically corrects phase and group- delay over typically 3ms window
  • Integrate one or two subwoofers with main speakers with time-correction
  • Provides anechoic measurement and detailed display for speaker correction
  • Patented low-latency FIR processing for speaker correction allows video use
  • Provides room-measurement/display (non-anechoic) for room correction
  • Auto and real-time manual Parametric EQ over measurement display
  • Remote tone control provides full-spectrum parametric EQ with 100-presets
  • DEQX integrated software measurement, correction and user-defined options
  • Two analog inputs: Unbalanced (2 x RCA) and Balanced (2 x XLR)
  • Two stereo digital inputs: S/PDIF (1 x RCA) and AES/EBU (1 x XLR)
  • Anodized Black aluminum front pane
  • Six analog outputs: unbalanced (6 x RCA)

  • Provides DEQX-HD™ speaker correction for up to 3-way active speakers
  • DEQX-HD™ active crossovers; 48dB/octave to 300dB/octave linear-phase
  • Traditional active 3-way crossovers from 6dB/octave to 48dB/octave
  • 32-bit, floating-point, 240-MFLOPS processing with dual SHARC DSPs
  • Audiophile op-amps typically 300V/uSec slew-rate with high output drive
  • Audiophile 24-bit 96kHz ADC-DSP-DAC processing and conversion
  • Four, user-defined 'Profiles' allow different crossovers, room-EQ, preferences
  • Remote controls; Volume, Profile, Input select, and Lo, Mid, Hi tone controls
  • Calibration Kit provides DEQX-calibrated measurement microphone optional extra
  • Individual driver correction prior to crossover when actively implemented
  • Microphone input has 48V phantom power for DEQX Calibrated™ mics
  • 100V-250VAC mains input
  • 2U high chassis; 3.5" H x 17" W x 11.5"
  • Online and telephone support
  • Free downloadable software and firmware updates


Standard Calibration Kit includes:       OR

  • DEQX Calibrated™ Behringer measurement microphone
  • Five-metre balanced microphone cable (XLR)
  • DEQX PC-based measurement, correction software on CD
  • Five-metre USB cable

Reference Calibration Kit Includes:

  • DEQX Calibrated™ EARTHWORKS measurement microphone
  • Five-metre balanced microphone cable (XLR)
  • DEQX PC-based measurement, correction software on CD
  • Five-metre USB cable

Additional OUTPUT options (6 x RCA unbalanced outputs are standard):

Electronic balanced analogue               OR
outputs (6 x XLR)

Jensen/DEQX transformer analogue balanced outputs (6 x XLR)