DEQX Products

Most people don’t realize that their speaker's frequency response, no matter its pedigree, is typically accurate only to within a 6dB window or nearly 6dB worse than the signal driving them! But DEQX handily reduces this to only about 1dB. Speaker timing and phase errors cause critical midband frequencies to lag behind others on the order of a millisecond or so. DEQX reduces these errors typically by fivefold!

The Platform
The HDP-Express sports dual 32-bit floating-point SHARC DSPs running firmware with patented digital processing technology that provides -140dB THD digital transparency and blazing low-latency, real-time performance. This ultra-reliable platform is complemented with high resolution ADC and DAC technology because the HDP-Express implements a pure 24bit/96kHz digital processing path.

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

The HDP-Express features these remote-control-selectable stereo inputs: S/PDIF (RCA), AES3 (XLR), Single-Ended Analog (RCA), and Balanced Analog (XLR). Four remote-control-selected profiles allow instant selection of different combinations of crossovers, correction filters, room EQ and Preference EQ… everything at your fingertips! Three channels of single-ended stereo line outputs are standard issue, providing bass (or sub/s), mid (or full-range) and treble signals for the amplifiers. Optional balanced output modules are available using either DEQX or Jensen transformer technologies.

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 speakers first via direct measurement, then apply corrected digital filtering to them. Once the speaker itself is working accurately, the HDP-Express measures again to provides room compensation for your newly-corrected speakers that address room effects.

Think of the HDP-Express as a Loop Processor that measure your speakers and applies sophisticated correction filters. There are two ways to become DEQXified. DEQX Inline™ works with your stereo ampilfier 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 one DEQX Inline to integrate, correct and time align one or a pair of subwoofers with main Left & 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 DEQX-ify and lower intrinsic distortion and add room compensation the world changes in an instant as the sound becomes startlingly more coherent. You’ll experience an astounding sense of realism that makes suspending disbelief and fully engaging with music or video easy.

Understand however that speaker correction and room compensation doesn’t actually increase your speaker's resolution, reduce breakup and crossover distortion, or improve dynamics and dispersion. To accomplish even more the HDP-Express provides 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 channelsper 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 stunning results. The steep linear-phase crossover filters keep each driver in their comfort zone of about four octaves. When you additionally reduce each driver’s break-up distortion, intermodulation and crossover distortion it further restores natural dispersion characteristics. The immediate effect is even greater resolution improving volume capacity, dynamics and slam. The immersive you-are-there realism is astounding when distortion is reduced to these levels. Adding DEQX XO to any speaker, regardless of type and cost, results in truly dramatic improvements in performance.

Avoiding unnecessary conversions the HDP-Express™ features preamp functions so when using digital input sources no additional ADC conversions are required that might compromise source signal integrity. Analog inputs are standard as well.

Although single-pole crossovers can provide near linear phase crossovers they provide almost no protection for tweeters and midrange drivers from typically big excursions, causing beak-up distortion, compression and reduced resolution. Single-pole crossovers also promote beaming in the higher frequencies which causes uneven dispersion and sounds unnatural in most rooms.

Compared to the significant phase distortion caused by steeper than single-pole filters (6dB/octave), or the significantly different problems caused by shallow single-pole filters (albeit more in linear-phase), DEQX provides 8-pole filters (48dB/octave) maintaining linear-phase and controlling undesirable driver excursions. This way we retain each driver’s 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… a stunning difference!

DEQX XO Linear-Phase Crossovers
We can't ignore the fact that very few speakers resolve their output to better than 1 or 2% best-case resolution, rising nearly tenfold by breakup distortion associated with louder dynamics. The loss of resolution occurs when drivers operate outside their comfort zone resulting in additional crossover distortion, unnatural or beaming dispersion characteristics, lobing plus 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 natural 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.

Although single-pole crossovers can provide near linear phase crossovers they provide almost no protection for tweeters and midrange drivers from typically big excursions causing beak-up distortion, compression and reduced resolution. Single-pole crossovers also promote beaming in the higher frequencies which causes uneven dispersion and sounds unnatural in most rooms.

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. DEQX adjusts phase and amplitude to differing degrees for numerous frequency groups getting to the root of the problem.

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 Inline setup. Then DEQX creates corresponding correction filters. These are FIR (Finite Impulse Response) filters that are quite unlike traditional EQ filters because, in their attempt to correct frequency-response errors, FIR filters actually maintain linear-phase. Traditional EQ filters actually introduce nonlinear errors! DEQX returns the actual measured timing coherence that corresponds 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 the DEQX-Cal™ software appropriately delays the faster groups until all groups are 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, except in the bass, for room compensation, which compromises phase accuracy when applied to midrange and high frequencies.

Once the speaker is corrected DEQX measures it again from the listening area and the results are displayed graphically 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 conveniently puts mastering engineer-level 3-band tone controls on a remote control! 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 "(what is Q)" 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 the HDP-EXPRESS. Blu-ray is only as good as your loudspeakers! Using a single HDP-EXPRESS to apply DEQX correction to just the front left and right speakers makes the centre speaker optional because DEQX Inline provides extraordinary 3D imaging due to uniform dispersion, low distortion and phase accuracy of each of the main Left/Right front 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 allows 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.

The Remote
Up to four different combinations of speaker and room corrections can be stored for instant recall by the HDP-Express. 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-EXPRESS passes up to 40kHz.