master the art of timing

The technology behind DEQX

So-called ‘room correction devices’ simply adjust amplitude response 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-4 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.


Your crossover or mine
To accomplish the HDP-EXPRESS and HDP-4 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 Inline setup. 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-4 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-4 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-4s to include a center channel and one or more subwoofers… the ultimate HT experience.

In addition to DEQX timing and frequency-response corrections, the HDP-EXPRESS and HDP-4 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.