No one talks about it much but the best-kept secret in audio is that there’s no speaker system on Earth than can keep up with the signal at the inputs. Even the most revered audiophile speakers introduce an astonishing 10-times more phase and timing errors than the signal driving them. Add to that a myriad of frequency-response errors piling on, plus a listening area that’s, in most cases, drenched in room reflections and it’s a wonder we can hear anything at all. But DEQX makes it easy to suspend disbelief and enter the world of music and video.

The Platform
The HDP-3 is a stereo digital processor packed with innovative DEQX-patented speaker and room compensation technology. It’s the ultimate DEQX implementation with upgraded power supplies and analog electronics. Connected to a PC running DEQX software during installation, HDP-3 measures and corrects your main speakers and subwoofers using its largely automated wizard-driven measurement, analysis, and correction software.

A problem with old-style DSP audio processing was its tendency to sound digital, flat and bright. In addition to its S/PDIF and AES3 digital inputs, the HDP-3 Preamp Processor features balanced and unbalanced analog inputs built around highly transparent Analog to Digital Converters (ADCs) running at 24-bits and 96kHz resolution.

Two SHARC 32-bit floating-point DSPs provide internal processing resolution on the order of 160dB followed by audiophile 24bit/96kHz 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 to provide the main analog rails, deliver extremely low measured distortion and fatigue-free listening. Almost half a million lines of software refined by our engineers over twelve years, distinguish DEQX from other digital processors and crossovers. Avoiding unnecessary conversions the HDP-3™ features preamp functions so when using digital input sources no additional DAC conversions are required that might compromise source signal integrity. 

The HDP-3 features these stereo digital and analog inputs: SPDIF (RCA), AES/EBU (XLR), Unbalanced Analog (RCA) and Balanced Analog (XLR). Standard outputs are Analog Unbalanced (RCA). Optional outputs include Balanced Analog (6 x XLR) or Digital outputs (3 x XLR, 3 x RCA). Multiple HDP-3s can connect for multichannel surround configurations such as 4.2 and 5.1 to 7.7.

You can use one HDP-3 to correct Left and Right front speakers plus one or more subwoofers – that’s where a soundtrack’s music lives for the most part. The HDP-3 automatically selects its digital input when sensing stereo PCM from a CD or DVD player up to 24-bit/96kHz, and defaults to its analog input for Front Left and Right soundtracks.

The preamplifier features of the HDP-3 include six digitally-controlled analog volume controls that allow the DACs to operate at their maximum resolution even at low listening levels. The remote control provides volume control, input selection, four different speaker and room correction profile selections, and low, mid and high frequency tone controls. The mid frequency control is a fully parametric EQ band. 99 tone control settings can be saved and recalled from the remote control!

Unlike other DSP room correction schemes that include room acoustic effects in their measurements, the HDP-3 measures and corrects a speaker’s native anechoic behavior so that frequency-related phase (group-delay) errors and frequency response errors are corrected before measuring again and compensating for room acoustics.

Up to four different combinations of speaker and room corrections can be stored for instant recall by the HDP-3. These include an uncorrected (bypass) mode to recall (and demonstrate for friends!) what your system sounded like before DEQXification!

The remote provides a three-band tone control so 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, while one of the digital inputs might be connected to digital sources like a CD or DVD player.

Calibration
If you’re not working with a DEQX installer and want to measure and correct the speakers and room yourself 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 Method
So-called “room correction devices” simply adjust amplitude response – uneven output at different frequencies -- to offset measured anomalies introduced by the room. But they don't address the phase or group-delay timing issues that are always present in 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.