HDP-3™ Preamp processor


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-3 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-3 first measures and corrects your speakers and subwoofers using its largely automated wizard-driven measurement, analysis, and correction software.

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

When using the HDP-3 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 160dB 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 HDP-3 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.


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-3 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.


  • DEQX-Cal™ Software and firmware provides software measurement, correction with user-defined options
  • Audiophile-grade analog electronics
  • Balanced analog input (2 x XLR)
  • Single-ended analog output standard (6 x RCA)
  • Digital Output Optional
  • Microphone input with 48V phantom power for DEQX Calibrated™ mics
  • 24-bit /96kHz ADC/DSP/DAC processing and conversion
  • Floating 32-bit DSP Digital Volume control
  • Provides anechoic measurement and detailed display for speaker correction
  • Provides room-measurement/display (non-anechoic) for room compensation
  • 48dB/octave to 300dB/octave linear-phase crossovers
  • Two analog inputs: Unbalanced (2 x RCA) and Balanced (2 x XLR)
  • Front-panel Volume Control and Profile selection
  • Auto and real-time manual Parametric EQ
  • Remote tone control provides full-spectrum parametric EQ with 100-presets
  • Individual driver correction when using active DEQX XO
  • Audiophile-grade linear power supply
  • Anodized Black or Silver aluminum front panel
  • Free downloadable software and firmware updates
  • Kit includes DEQX-calibrated microphone
  • Stereo digital inputs: SPDIF (1 x RCA) and AES/EBU (1 x XLR)
  • Single-ended analog input (2 x RCA)
  • Balanced output optional (6 x XLR)
  • Analog power supply
  • High-performance op-amps typically 300V/uSec slew-rate with high output drive
  • 32-bit Floating Point 240-MFLOPS processing with dual SHARC DSPs
  • Automatically corrects phase and group-delay over typical 3ms window
  • Patented low-latency FIR processing for speaker correction
  • Active 3-way crossovers from 6dB/octave to 48dB/octave
  • Calibration Kit provides DEQX-calibrated measurement microphone
  • Speaker frequency-response typically corrected from 6dB range to 1dB*
  • Four user-defined Profiles allow different crossovers, room-EQ
  • Remote includes Volume, Profile, Input select plus Lo, Mid, Hi tone controls
  • Analog volume control maintains full DAC resolution at low listening levels
  • D115V-230VAC mains input; 30VA (100V-200V Japan-only option)
  • 2U chassis; 3.5" H x 17" W x 11.5"
  • Membership in DEQX online Users Group
  • Online and telephone support

Calibration kits (option)

A Calibration kit is used for setting up all DEQX units. Each includes the DEQX measurement, analysis and correction software for PC and USB cable as well as a DEQX Calibrated™ measurement microphone with cable.

A boom microphone stand (not supplied) is required for speaker and room measurements. Stands are typically available for under $100 from a local musical instrument supply shop.

For high-end speaker correction, the Reference calibration kit is recommended due to its high performance, higher bandwidth Earthworks microphone.

Standard Calibration Kit

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

Reference Calibration Kit

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

Optional output modules

The HDP-3 can accept either of the balanced output modules. Both modules are an optional upgrade. In addition, it can accept the digital output upgrade module.

The HDP-3 rear panel allows field installation of all three optional output modules. Standard units have blanking plates covering the analogue and digital output sections, so it is possible to install optional output modules at a later time if necessary.

Balanced Out 'HD' Module

Provides six electronically balanced XLR outputs. The ‘HD’ version uses CD servos to avoid the use of series capacitors, and uses late generation extremely high slew rate op-amps for an ‘open’ 3D sound with great resolution and unconstricted detail.

Balanced Out Transformer Module

Provides six transformer-balanced XLR outputs. This modules uses six Jensen output transformers that provide complete galvanic isolation form ground noise, while providing excellent transparency.

Digital Out Module

The digital output module provides three stereo AES/EBU outputs via three XLR connectors. The unit also provides three stereo S/PDIF outputs via RCA connectors.

It also provides a fourth female XLR that will accept an AES sync input that will asynchronously sync all digital outputs to the input clock reference up to 100kHz sample rate, regardless of the input or processing sample rate.