DEQX hdp-4 preamp

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Sold Out. The HDP-5 is the replacement.

The HDP-4 is the Reference Level DEQX Calibrated. Now with 32bit/192kHz resolution and USB input module with a world-class digital front end. Take your good speakers to greatness and your great speakers to the ultimate reference level!

The HDP-4 arrives at your door with many options as standard like digital and active balanced analog outputs for all three channels. The HDP-4 gives you everything the HDP-3 delivered plus valuable options, more digital inputs, a USB audio option, three new generation Burr-Brown 32-bit DACs, new Cirrus Logic ADC, an upsampling/reclocking feature, an audiophile-grade chassis with sturdy case-mounted connectors and a gorgeous 12mm brushed aluminum faceplate available in Silver or Black.

Each of the three digital output channels is equipped with SPDIF 75-ohm BNC connectors. The fourth digital output is a Digital DSP Input Pass-Through for slaving selected digital inputs for further processing. On the input side, the HDP-4 now supports 24/192, a TOSLINK optical input and there’s an optional USB digital audio input module coming soon.

Now includes DEQX XS-1 USB Audio Board For Macs or PCs

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-4, like the HDP-3 and HDP-Express, is a stereo digital processor than can be installed between preamp and amplifier or more directly used 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-4 first measures and corrects your speakers and subwoofers using its largely automated wizard-driven measurement, analysis, and correction software.

The new HDP-4 is an HDP-3 gone ultra-rez offering 24/176.4 and 24/192 digital inputs, a feature many of you have asked for. The '4 now supports TOSLINK input plus an optional USB input module. Stereo digital and analog inputs include SPDIF, AES/EBU, unbalanced analog and balanced analog.

The HDP-4 comes with many output options standard like SPDIF on true 75 ohm BNC connectors, balanced analog outputs, with another digital output configured as a DSP Input Pass-Through for connecting selected inputs for further processing

When using the HDP-4 as a 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. See the Features Tab for more details.

While the DEQX HDP-4 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.

The HDP-4 gives you everything the '3 delivered plus valuable output options as standard, it has more digital inputs, a USB audio option, 32-bit/192kHz DACs, a new circuit board, an audiophile-grade chassis with sturdy case-mounted connectors and a handsome 12mm brushed aluminum faceplate available in Silver or Black.


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 Kitor 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.

DEQX processors are unique… they address the shortcomings of the speaker first via direct measurement, and then apply corrected digital filtering. Once the speaker is working accurately the HDP-EXPRESS and HDP-3 measure again and provides room compensation for your newly-corrected speakers.

Think of them as Pre-Amp Processors that measure your speakers and apply sophisticated correction filters. There are two ways to DEQXify. DEQX Inline works with your stereo amplifier and speakers as a complete package, also called a passive setup. In a typical audio system you might use the six available DSP channels to optimize a 1-way, a 1-way plus sub(s), a 2-way, or a 2-way plus sub(s) system.

A popular home theater setup is a single DEQX Inline to integrate, correct and time align one or a pair of subwoofers with main Left and Right speakers, and then adds room compensation and Preference EQ. A remote control for a 3-band equalizer with one fully parametric band adjustable across ten octaves makes fine tuning easy.

DEQX Inline’s powerful DSP technology is transparent to the speaker’s internal crossover and measures the cumulative output of your speakers and corrects for amplitude balance (frequency response), phase, group-delay and timing errors thus vastly improving the immersive experience.

When you DEQXify and lower intrinsic distortion and add room compensation the presentation changes in an instant as the sound becomes startlingly more coherent. You’ll experience a surprising sense of realism that makes suspending disbelief and fully engaging with music or video easy.

DEQX XS-1 USB Audio Board

DEQX XS-1 24/192 Asynchronous USB board.

This digital input board allows you to connect your DEQX directly to your Windows or Mac based music servers.

If you use a music server, this is the best sounding way to get sound into your DEQX!

USB Board Features:

16/44 - 24/192 Asynchronous

No 5v power connection to computer; powered internally from ultra clean DEQX power supply.

I2S interface to eliminate conversation to SPDIF and reduce jitter.

Interdependent regulated clocks.

No drivers required for Macintosh OSX.

Windows Drivers supplied for XP, Vista, Windows 7, Windows 8 32 & 64 bit.

DEQX HDP firmware update supplied on disc.

Easy to install, just one plug.

Your Crossover or Mine
To accomplish the HDP-EXPRESS and HDP-3 provide an upgrade path from DEQX Inline to DEQX XO™ using high-order crossover filters that maintain true linear-phase and individual driver correction.

Top-of-the-line DEQX XO does away with traditional crossovers with their traditional problems. Instead it’s amplifier-direct, replacing the passive crossover with up to three DSP-equalized channels per side driving the amplifiers for each driver, also known as active tri-amping in a traditional 3-way, although DEQX goes far beyond traditional active systems.

DEQX XO gives the processor direct control of the signal feeding each driver producing even more breathtaking results. The steep linear-phase crossover filters keep each driver in their comfort zone of about four octaves. Reducing each driver’s break-up distortion, intermodulation and crossover distortion further restores natural dispersion characteristics. When distortion is reduced to these extraordinary levels the effect is even greater resolution, improved volume capacity, dynamics and slam delivering immersive you-are-there realism. Adding DEQX XO to any speaker, regardless of type or cost, results in dramatic improvements.

Timing and Frequency-Response Correction
A speaker's frequency response is a measure of its success in reproducing all frequencies at exactly the same relative volume. Very few speakers can achieve this more accurately than within a 6dB window (+/-3dB). DEQX products correct this to within a one-decibel window (+/-0.5dB subject to measurement accuracy).

Varying degrees of correction are required for different frequencies and improvements are usually most noticeable through the midrange as DEQX's patented DSP process effectively slows down on-time frequencies so that latecomers catch up!

Unfortunately correcting frequency response isn’t enough. Another fundamental consideration is time; the phase of all frequencies must maintain linearity to sound natural and that’s called linear phase. Uncompensated speakers cannot deliver accurate amplitude with all frequencies in phase and on time. The different timing delays that occur for different frequency groups are known as group-delay errors.

Steep and Shallow Single-Pole Crossovers
While single-pole crossovers are capable of linear phase they provide almost no protection at all for tweeters and midrange drivers from unfortunate driver excursions that causes beak-up distortion, compression and reduced resolution. Single-pole crossovers also promote beaming in the upper frequencies which causes uneven dispersion that sounds unnatural in most rooms.

Compared to the significant phase distortion caused by steeper-than-single-pole filters (6dB/octave) or the altogether different problems caused by shallow single-pole filters (albeit more in linear-phase), DEQX provides 8-pole filters (48dB/octave) that maintain linear-phase and will control errant driver excursions. Each driver then delivers best-case resolution while providing some driver overlap.

Significant reductions in dynamic, crossover, break-up distortion and compression takes a lot of computational horsepower, but the result is unprecedented accuracy in timing and frequency response, a dramatic reduction of breakup and crossover distortion, with louder distortion-free dynamics and slam, with improved natural dispersion… stunning!

DEQX XO Linear-Phase Crossovers
Very few speakers resolve their output to better than 1 or 2% best-case resolution, rising nearly tenfold by breakup distortion associated with high dynamics. The loss of resolution occurs when drivers operate outside their comfort zone resulting in additional crossover distortion, unnatural or beaming dispersion characteristics, lobing and noticeable volume limitations.

Traditional crossover filters (other than the most shallow 1st-order 6dB/octave designs) are nonlinear and known to introduce phase distortion. Implementing linear-phase, rather than minimum-phase filters virtually eliminates crossover distortion while dramatically improving dispersion. The narrow crossover transition also eliminates crossover comb-filtering effects. DEQX products are some of the very few offering these desirable steep linear phase crossovers -- typically four-times steeper than almost all passive crossovers!

The Critical Difference
Other DSP active crossovers typically simulate traditional analog filters and a few also provide parametric EQ and what they call timing correction. These filters are not linear phase and timing correction simply allows one driver to be delayed (time-aligned) with another. While time alignment is essential it can’t correct the numerous group-delay errors (frequency related phase) introduced by the drivers themselves. Getting to the root of the problem DEQX adjusts phase and amplitude by differing degrees for various frequency groups.

DEQX achieves this automatically by analyzing the pseudo-anechoic native measurements of each speaker driver in an active DEQX XO system, or the overall speaker response in a passive DEQX Inlinesetup. Then DEQX creates corresponding correction filters. These are FIR (Finite Impulse Response) filters that are unlike traditional EQ filters because, in their attempt to correct frequency response errors they will maintain linear phase.

Traditional EQ filters actually introduce nonlinear errors. But DEQX returns the actual measured timing coherence corresponding to the original audio signal while frequency response errors are corrected in a similar way. The measurement and analysis procedure detects which frequency groups are being comparatively delayed and DEQX CAL™ software appropriately delays the faster groups until they’re all coherent.

Room Compensation
Typical DSP-based room correction systems measure a mix of your speaker's direct output plus room effects. DEQX speaker correction measurements ignore room reflections in determining accurate native anechoic speaker performance in the time domain (phase and group delay) as well as frequency domain (frequency response). After a speaker’s native frequency response and dispersion characteristics have been corrected there’s less required for room compensation except in the bass avoiding compromising phase accuracy in the midrange and high frequencies.

Once the speaker is corrected DEQX measures it again from the listening area and the results are displayed graphically on the setup PC. Typically only three to six bands of DEQX’s parametric EQ are required to resolve in-room bass issues and can be set automatically or manually to preference.

Media Correction
Lots of enthusiasts feel that some of their favorite recordings simply need a bit of tone control, a valid reason for having them despite their wide-ranging effects over many octaves. The HDP-EXPRESS and HDP-3 conveniently put mastering engineer-level 3-band tone controls on the remote! It features a bass-shelf, a fully parametric equalizer adjustable across ten octaves, and a high-shelf. The three center frequencies are adjustable across octaves and semitones, and Q – the driver’s damping factor -- is adjustable from one semitone to four-octaves wide. Some recordings are worth spending a minute or two getting exactly right after which your settings can be saved to one of 99 memory positions for later recall.

Stereo and Multichannel Surround Sound
Surround recordings and video soundtracks take on a breathtaking new realism with DEQX. After all, Blu-ray is only as good as your speakers! Using a single HDP-EXPRESS or HDP-3 to apply correction to just the front Left and Right speakers makes the Center speaker optional as DEQX Inline provides extraordinary 3D imaging due to uniform dispersion, low distortion and phase accuracy of each of the main speakers. You may find the phantom center image more than you need, although many people deploy multiple HDP-EXPRESS or HDP-3s to include a center channel and one or more subwoofers… the ultimate HT experience.

Beyond DEQX timing and frequency-response corrections, the HDP-EXPRESS and HDP-3 allow seamless integration of mono or stereo subwoofers so the crossover from the main speaker and subwoofer/s can be time-aligned using measured or real-time adjustment by ear.



  • DEQX integrated software measurement, correction with user-defined options
  • Kit includes DEQX-calibrated microphone
  • Audiophile-grade analog electronics
  • Stereo 24/176.4 and 24/196 digital inputs: SPDIF (1 x RCA and 1 x BNC) AES/EBU (1 x XLR)
  • Balanced analog input (2 x XLR)
  • Single-ended analog input (2 x RCA)
  • TOSLINK input
  • Optional USB input
  • Bypass DSP input-pass-output
  • Balanced output (6 x XLR)
  • Single-ended output (6 x RCA)
  • DC-coupled analog outputs
  • Analog power supply
  • Microphone input with 48V phantom power for DEQX Calibrated™ mics
  • High-performance op-amps typically 300V/uSec slew-rate with high output drive
  • 24-bit /96kHz ADC/DSP/DAC processing and conversion
  • 32-bit Floating Point 240-MFLOPS processing with dual SHARC DSPs
  • Floating 32-bit DSP Digital Volume control
  • Automatically corrects phase and group-delay over typical 3ms window
  • Provides anechoic measurement and detailed display for speaker correction
  • Patented low-latency FIR processing for speaker correction
  • Provides room-measurement/display (non-anechoic) for room compensation
  • Active 3-way crossovers from 6dB/octave to 48dB/octave
  • 48dB/octave to 300dB/octave linear-phase crossovers
  • Speaker frequency-response typically corrected from 6dB range to 1dB*
  • Front-panel Volume Control and Profile selection
  • Four user-defined Profiles allow different crossovers, room-EQ
  • Auto and real-time manual Parametric EQ
  • Remote includes Volume, Profile, Input select plus Lo, Mid, Hi tone controls
  • Remote tone control provides full-spectrum parametric EQ with 100-presets
  • Individual driver correction when using active DEQX XO
  • D115V-230VAC mains input; 30VA (100V-200V Japan-only option)
  • Audiophile-grade linear power supply
  • 2U chassis; 3.5" H x 17" W x 11.5"
  • Anodized Black or Silver aluminum front panel
  • Membership in DEQX online Users Group
  • Free downloadable software and firmware updates
  • Online and telephone support


  • Stereo analog inputs, balanced (XLR) and unbalanced (RCA)
  • Stereo digital inputs, S/PDIF and AES/EBU
  • Six analog outputs, unbalanced RCA
  • Mic input for optional DEQX Calibrated™ measurement microphone

Standard Calibration Kit includes

  • 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 microphoneFive-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 outputs (6 x XLR)
  • OR

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

  • Digital outputs; S/PDIF (3 x RCA) and AES/EBU (3 x XLR). One AES sync input (XLR) allows Sample Rate Conversion (SRC) asynchronous re-clocking of all digital outputs to the input reference clock 24-bit,100kHz max (auto-sense input clock)




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